Showing 1–50 of 75 results for author: Gan, W

Multiwavelength spectroscopic observations of a quiescent prominence

Authors: Jianchao Xue, Ping Zhang, Jean-Claude Vial, Li Feng, Maciej Zapiór, Werner Curdt, Hui Li, Weiqun Gan

Abstract: In this paper we focus on the analysis of the multiwavelength spectroscopic observations of a quiescent prominence. The spectral and geometrical parameters in the prominence were derived and used to constrain the NLTE radiative transfer models. Applying this method with multiwavelength observations provides a good opportunity to reduce the large range of thermodynamic parameters in solar prominenc… ▽ More In this paper we focus on the analysis of the multiwavelength spectroscopic observations of a quiescent prominence. The spectral and geometrical parameters in the prominence were derived and used to constrain the NLTE radiative transfer models. Applying this method with multiwavelength observations provides a good opportunity to reduce the large range of thermodynamic parameters in solar prominences. We used time-slice and optical flow methods in order to derive the plane-of-sky (POS) velocities, and used gravity center and peak position methods on Mg II h&k and H I Ly-alpha profiles to compute the line-of-sight (LOS) velocities. We used the integrated intensities and FWHM values of the H-alpha, Ca II H, and Mg II h&k lines to compare with the NLTE radiative transfer computations. Ionization degree and thickness of the prominence plasma could be further derived. Opposite flows are observed along two strands between prominence barbs. The POS velocity can reach 20 km/s and the largest LOS velocity is > 90 km/s. The derived electron densities range from 6.5e9 cm-3 to 2.7e10 cm-3, and the derived total hydrogen densities range from 7.4e9 cm-3 to 6.6e10 cm-3. The temperature ranges from 7 000 to 14 000 K. The ionization degree of hydrogen is in the range of 0.40 to 0.91. The comparison between averaged and modeled profiles of Mg II and Ly-alpha lines shows that macro-velocities of 15 km/s and 20 km/s are required, respectively. The bulk motions among prominence barbs indicate that the prominence plasma is not confined within magnetic dips but exhibits a large-scale behavior. The presence of high-speed cool plasma flows, along with a wide range of plasma densities and temperatures, suggests that the prominence plasma is far from thermodynamic equilibrium and is inherently dynamic in nature. △ Less

Submitted 17 October, 2025; originally announced October 2025.

Comments: Accepted by A&A

Quantum Damping of Cosmological Shear: A New Prediction from Loop Quantum Cosmologies

Authors: Wen-Cong Gan, Leila L. Graef, Rudnei O. Ramos, Gustavo S. Vicente, Anzhong Wang

Abstract: We analyze the dynamics of the Bianchi I universe in modified loop quantum cosmology (Model I, or mLQC-I), uncovering a robust mechanism for isotropization. As in the standard LQC, the classical singularities are resolved by quantum bounce. Remarkably, mLQC-I exhibits a distinctive feature: following the bounce, the shear is dynamically suppressed and decays rapidly to zero within the deep quantum… ▽ More We analyze the dynamics of the Bianchi I universe in modified loop quantum cosmology (Model I, or mLQC-I), uncovering a robust mechanism for isotropization. As in the standard LQC, the classical singularities are resolved by quantum bounce. Remarkably, mLQC-I exhibits a distinctive feature: following the bounce, the shear is dynamically suppressed and decays rapidly to zero within the deep quantum regime. This occurs independently of the collapsing matter fields, leading to a natural quantum isotropization. Consequently, the three spatial directions expand rapidly to macroscopic scales, producing a homogeneous and isotropic universe directly from the quantum epoch without fine-tuning. Our findings demonstrate that mLQC-I not only resolves singularities but also provides a more effective pathway for suppressing anisotropies than other models, thereby reinforcing its viability as a description of the early universe. △ Less

Submitted 15 October, 2025; originally announced October 2025.

Comments: revtex4-2, 2 figures and no table

The Role of Far-side Magnetic Structures in Modeling 2024 Solar Eclipse

Authors: Guanglu Shi, Jiahui Shan, Li Feng, Jun Chen, Weiqun Gan

Abstract: The corona is a crucial region that connects the solar surface to the solar wind and serves as the primary site of solar activity. The 2024 total solar eclipse (TSE) provides a unique opportunity to investigate the large-scale coronal structure. Combined with TSE observations, we study the impact of the magnetic structure of the far-side active region, located in the eastern hemisphere of the Sun… ▽ More The corona is a crucial region that connects the solar surface to the solar wind and serves as the primary site of solar activity. The 2024 total solar eclipse (TSE) provides a unique opportunity to investigate the large-scale coronal structure. Combined with TSE observations, we study the impact of the magnetic structure of the far-side active region, located in the eastern hemisphere of the Sun that has not yet rotated into the Earth Field-of-View (FoV), on a global Magnetohydrodynamic (MHD) simulation. To address the limitation of single-view measurements in the routine synoptic map, we correct the magnetic field in the far-side region by incorporating full-disk magnetograms measured several days after the TSE, allowing us to capture the temporal evolution of the photospheric magnetic field in near real-time. Simulation results demonstrate that the local magnetic field in the far-side active region can significantly influence the global coronal structure by altering the position of the heliospheric current sheet (HCS), and further affect the global distribution of plasma parameters, even in polar regions. A comparison of the simulation results with white-light (WL) TSE + LASCO C2 observations and in situ measurements by the Parker Solar Probe (PSP) reveals that the composite synoptic map improves the accuracy of coronal modeling. This work provides robust support for advancing our understanding of coronal evolution, as well as deepens the link between the photosphere and large-scale coronal structure. Furthermore, it establishes a theoretical foundation for the future development of multi-view, stereoscopic measurements of the photospheric magnetic field. △ Less

Submitted 2 September, 2025; originally announced September 2025.

Comments: 15 pages, 6 figures, accepted for publication in ApJ

Early Evolution of the Cavity and Core of a Coronal Mass Ejection in the Inner Corona

Authors: Shuting Li, Li Feng, Beili Ying, Hongqiang Song, Guanglu Shi, Jiahui Shan, Jie Zhao, Weiqun Gan

Abstract: Coronal mass ejections (CMEs) typically exhibit a three-component structure in white-light (WL) coronagraphs. Utilizing the seamless observations of the inner corona ($\le$ 3 R$_\odot$), we have revealed the early evolution of the cavity and core of a CME starting at $\sim$18:20 UT on 2014 October 14. The CME originates from a hot channel (HC), which appears as the bright core and compresses the c… ▽ More Coronal mass ejections (CMEs) typically exhibit a three-component structure in white-light (WL) coronagraphs. Utilizing the seamless observations of the inner corona ($\le$ 3 R$_\odot$), we have revealed the early evolution of the cavity and core of a CME starting at $\sim$18:20 UT on 2014 October 14. The CME originates from a hot channel (HC), which appears as the bright core and compresses the cavity in WL images. Specifically, most of the dark cavity in WL is filled by bright loop-like structures in 174 Å. The differential emission measure (DEM) analysis indicates that the electron temperature decreases from the core ($\sim$13.4 MK) to the cavity ($\sim$1.35 MK), and the CME cavity is significantly cooler than that enshrouding a prominence ($\ge$ 2 MK). The effective temperature of the cavity increases over time in general, probably due to the compression by the HC expansion. The evolution of the CME bright core includes slow-rise, fast-rise (up to $\sim$330 km s$^{-1}$), and residual-acceleration phases. The cavity exhibits an evolution similar to the core but lags by $\sim$4 minutes, with a lower speed peaking at $\sim$220 km s$^{-1}$. Moreover, the 2D radial speed distribution exhibits the highest speeds at the core apex. The kinematical results further confirm the compression of the cavity. The present event supports the new explanation of the CME structures, i.e., the magnetic flux rope (MFR), which is proxied by the HC, is only responsible for the core, while the cavity is likely a low-density region between the CME front and the MFR. △ Less

Submitted 20 August, 2025; originally announced August 2025.

Comments: 17 pages, 7 figures

Probing Solar Polar Regions

Authors: Yuanyong Deng, Hui Tian, Jie Jiang, Shuhong Yang, Hao Li, Robert Cameron, Laurent Gizon, Louise Harra, Robert F. Wimmer-Schweingruber, Frédéric Auchère, Xianyong Bai, Luis Bellot Rubio, Linjie Chen, Pengfei Chen, Lakshmi Pradeep Chitta, Jackie Davies, Fabio Favata, Li Feng, Xueshang Feng, Weiqun Gan, Don Hassler, Jiansen He, Junfeng Hou, Zhenyong Hou, Chunlan Jin , et al. (23 additional authors not shown)

Abstract: The magnetic fields and dynamical processes in the solar polar regions play a crucial role in the solar magnetic cycle and in supplying mass and energy to the fast solar wind, ultimately being vital in controlling solar activities and driving space weather. Despite numerous efforts to explore these regions, to date no imaging observations of the Sun's poles have been achieved from vantage points o… ▽ More The magnetic fields and dynamical processes in the solar polar regions play a crucial role in the solar magnetic cycle and in supplying mass and energy to the fast solar wind, ultimately being vital in controlling solar activities and driving space weather. Despite numerous efforts to explore these regions, to date no imaging observations of the Sun's poles have been achieved from vantage points out of the ecliptic plane, leaving their behavior and evolution poorly understood. This observation gap has left three top-level scientific questions unanswered, 1) How does the solar dynamo work and drive the solar magnetic cycle? 2) What drives the fast solar wind? 3) How do space weather processes globally originate from the Sun and propagate throughout the solar system? The Solar Polar-orbit Observatory (SPO) mission, a solar polar exploration spacecraft, is proposed to address these three unanswered scientific questions by imaging the Sun's poles from high heliolatitudes. In order to achieve its scientific goals, SPO will carry six remote-sensing and four in-situ instruments to measure the vector magnetic fields and Doppler velocity fields in the photosphere, to observed the Sun in the extreme ultraviolet, X-ray, and radio wavelengths, to image the corona and the heliosphere up to 45 $R_\odot$, and to perform in-situ detection of magnetic fields, and low- and high-energy particles in the solar wind. △ Less

Submitted 16 September, 2025; v1 submitted 25 June, 2025; originally announced June 2025.

Comments: Accepted for publication in Chinese Journal of Space Science. Volume 45, Issue 4: 913 - 942 (2025)

Intense Hard X-ray Emissions in C-class Flares: A Statistical Study with ASO-S/HXI Data

Authors: Changxue Chen, Yang Su, Wei Chen, Jingwei Li, Fu Yu, Weiqun Gan

Abstract: In the standard model of solar eruptive events, coronal mass ejections (CMEs) and flares are associated with each other through magnetic reconnection initiated by erupting flux ropes. Observations also reveal an increasing association ratio between flares and CMEs with flare intensity. However, the fundamental relationship between flares and CMEs, and that between thermal and nonthermal processes,… ▽ More In the standard model of solar eruptive events, coronal mass ejections (CMEs) and flares are associated with each other through magnetic reconnection initiated by erupting flux ropes. Observations also reveal an increasing association ratio between flares and CMEs with flare intensity. However, the fundamental relationship between flares and CMEs, and that between thermal and nonthermal processes, remains unknown. Here we investigate energetic C-class flares (ECFs) -- Geostationary Operational Environmental Satellite (GOES) C-class flares with hard X-ray (HXR) emissions above 30 keV -- using observations from Advanced Space-based Solar Observatory/Hard X-ray Imager (HXI), Solar Dynamic Observatory, and GOES. Among 1331 C-class flares detected by HXI, 127 ECFs (9.5%) were identified for statistical analysis of their properties and associations with CMEs and other flare-related features. Our statistical results reveal that ECFs have relatively shorter durations and harder spectra (the mean electron power-law index is 4.65), with no significant correlation between soft X-ray flux and nonthermal parameters (e.g., HXR peak flux). Among the 127 events, 53 (42%) were associated with type III bursts, 38 (30%) with jets, at least 13 (~11%) with 360 nm brightenings, and only 5 (~4%) with CMEs. Crucially, all five CME events were narrow CMEs associated with jets. The surprising correlation between these ECFs and CMEs suggests that noneruptive or confined magnetic field configurations in these flares may favor electron acceleration, resulting in harder X-ray spectra.We discuss the potential formation mechanisms and efficient electron acceleration processes in these atypical flares, providing valuable insights into nonstandard flare behavior. △ Less

Submitted 23 June, 2025; v1 submitted 13 June, 2025; originally announced June 2025.

Comments: 14 pages, 5 figures, 1 table, Accepted in ApJL

Understanding the Lyα Emission Observed by the Solar Disk Imager Aboard the Advanced Space-based Solar Observatory

Authors: Yiliang Li, Ping Zhang, Zhengyuan Tian, Li Feng, Guanglu Shi, Jianchao Xue, Ying Li, Jun Tian, Kaifan Ji, Beili Ying, Lei Lu, Shuting Li, Jiahui Shan, Hui Li, Weiqun Gan

Abstract: The H I Lyman-alpha (Ly$α$) emission, with a wavelength of 1216 Å, is the brightest solar ultraviolet (UV) line. However, comprehensive observations of the Ly$α$ emission line across the full solar disk remain limited. As part of the ASO-S mission, the Solar Disk Imager (SDI) has successfully captured full-disk images in the Ly$α$ band. Gaussian fitting of SDI's spectral response function (SRF) yi… ▽ More The H I Lyman-alpha (Ly$α$) emission, with a wavelength of 1216 Å, is the brightest solar ultraviolet (UV) line. However, comprehensive observations of the Ly$α$ emission line across the full solar disk remain limited. As part of the ASO-S mission, the Solar Disk Imager (SDI) has successfully captured full-disk images in the Ly$α$ band. Gaussian fitting of SDI's spectral response function (SRF) yields a full width at half maximum (FWHM) of approximately 85 Å, which is significantly broader than the distance of Si III line at 1206 Å and the Ly$α$ line. Thus, the emission contribution of Si III to the SDI Ly$α$ passband needs to be considered. For flares, in practice, we calculated the integrated intensity ratio $I$(Si III)/$I$(Ly$α$) by analyzing spectral observations from the SOLSTICE instrument. It yields values between 1.7% and 14.6%. Empirically, the ratio is proportional to the SXR flux. Further analysis of spectral data from the SUMER instrument reveals that the ratio $I$(Si III)/$I$(Ly$α$) is approximately 0.5% for prominences, 0.7%--0.9% for the inner disk, and 1.4%--1.9% close to the limb. These findings suggest that $I$(Si III)/$I$(Ly$α$) is minimal for prominences and the inner disk, and the varying ratios across regions align with the center-to-limb variation of the Si III and Ly$α$ lines. Additionally, we compared Ly$α$ image intensity with 304 Å, 1600 Å, and 1700 Å observations from AIA, as well as H$α$ from CHASE, in multiple regions (a prominence region, two active regions, and a quiet region). A relatively higher correlation of about 85% is found between Ly$α$ and 304 Å in active regions, whereas in the quiet region and prominence, their correlation coefficients are about 55%. △ Less

Submitted 22 May, 2025; originally announced May 2025.

Magnetic energies (and some other parameters) in solar active regions of different Hale and McIntosh classes: statistical analysis for 2010-2024

Authors: I. V. Zimovets, I. N. Sharykin, W. -Q. Gan

Abstract: A statistical analysis of magnetic energies of the nonlinear force-free and potential fields, and their difference (a proxy for the free magnetic energy) in active regions (ARs) on the Sun of different Hale (Mount Wilson) and McIntosh classes for the period from May 1, 2010 to June 12, 2024 is presented. The magnetic fields in ARs are calculated using the GX Simulator based on the information abou… ▽ More A statistical analysis of magnetic energies of the nonlinear force-free and potential fields, and their difference (a proxy for the free magnetic energy) in active regions (ARs) on the Sun of different Hale (Mount Wilson) and McIntosh classes for the period from May 1, 2010 to June 12, 2024 is presented. The magnetic fields in ARs are calculated using the GX Simulator based on the information about ARs contained in the daily Solar Region Summary (SRS) files provided by the NOAA SWPC and vector magnetograms by the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO). Total unsigned and signed magnetic fluxes and vertical electric currents on the photosphere are also calculated. For the parameters considered, distributions have been determined in total for all ARs and separately for each Hale and McIntosh class. Minimum, maximum, mean values of the parameters and standard deviations were calculated for each class. The information about the parameters is presented in the form of graphs and tables. The magnetic energies, unsigned magnetic flux, unsigned vertical current, as well as the integral number of sunspots, number of ARs, and area of sunspots, integrated over ARs visible per day on the solar disk, exhibit similar approximately 11.6-year cyclicity. On average, magnetic energies of ARs increase with increasing Hale and McIntosh class, while the average fraction of the free magnetic energy in ARs of different classes differs weakly. We also found that the Poisson Flare Probabilities (PFPs) correlate with the parameters, and the Pearson correlation coefficient is up to 0.89. The results reveal relationships between various parameters of ARs and may be used in developing prediction of space weather effects. △ Less

Submitted 12 April, 2025; originally announced April 2025.

Comments: 34 pages, 8 figures, 3 tables, accepted to the Cosmic Research journal

Unveiling Spatiotemporal Properties of the Quasi-periodic Pulsations in the Balmer Continuum at 3600 Å in an X-class Solar White-light Flare

Authors: De-Chao Song, Marie Dominique, Ivan Zimovets, Qiao Li, Ying Li, Fu Yu, Yang Su, B. A. Nizamov, Ya Wang, Andrea Francesco Battaglia, Jun Tian, Li Feng, Hui Li, W. Q. Gan

Abstract: Quasi-periodic pulsations (QPPs) in the Balmer continuum of solar white-light flares (WLFs) are rarely reported, and accurately pinpointing the spatial source of flaring QPPs remains a significant challenge. We present spatiotemporal characteristics of QPPs of an X2.8 two-ribbon solar WLF (SOL2023-12-14T17:02), which was well observed by the White-light Solar Telescope (WST) aboard the Advanced Sp… ▽ More Quasi-periodic pulsations (QPPs) in the Balmer continuum of solar white-light flares (WLFs) are rarely reported, and accurately pinpointing the spatial source of flaring QPPs remains a significant challenge. We present spatiotemporal characteristics of QPPs of an X2.8 two-ribbon solar WLF (SOL2023-12-14T17:02), which was well observed by the White-light Solar Telescope (WST) aboard the Advanced Space-based Solar Observatory, with high-cadence imaging (1--2 s) in the Balmer continuum at 3600 Å. Combined with additional multi-instrument data, we find that the enhancement of the WLF in both Balmer and Paschen continua shows strong spatiotemporal correlation with hard X-ray (HXR) emissions. Notably, the pulses in the WST Balmer continuum exhibited a near-zero time lag with most HXR pulses, whereas soft X-ray and extreme ultraviolet emissions showed a lag of 2--3 s. Interestingly, quasi-harmonic QPPs with periods of $\sim$11 s and $\sim$20 s were observed in multiple wavelengths in the rising phase of the white-light continuum. Furthermore, we employed Fourier transform to spatially locate the QPPs around 11 and 20 s, revealing that they primarily originated from the east flare ribbon, which exhibited the most substantial continuum enhancement. More interestingly, we find that the west ribbon contributed significantly to the 11-second QPP but had a weaker contribution to the 20-second QPP. Moreover, the occurrence of quasi-harmonic QPPs is temporally coincident with the rapid elongation and separation motions of flare ribbons. Possible mechanisms for the quasi-harmonic QPPs have been discussed. These observations provide valuable insights into QPP modeling for solar and stellar flares. △ Less

Submitted 3 April, 2025; originally announced April 2025.

Comments: 19 pages, 6 figures, and two tables

MSC Class: 85 ACM Class: J.2

Massive stars exploding in a He-rich circumstellar medium $-$ X. Flash spectral features in the Type Ibn SN 2019cj and observations of SN 2018jmt

Authors: Z. -Y. Wang, A. Pastorello, K. Maeda, A. Reguitti, Y. -Z. Cai, D. Andrew Howell, S. Benetti, D. Buckley, E. Cappellaro, R. Carini, R. Cartier, T. -W. Chen, N. Elias-Rosa, Q. -L. Fang, A. Gal-Yam, A. Gangopadhyay, M. Gromadzki, W. -P. Gan, D. Hiramatsu, M. -K. Hu, C. Inserra, C. McCully, M. Nicholl, F. E. Olivares, G. Pignata , et al. (26 additional authors not shown)

Abstract: We present optical and near-infrared observations of two Type Ibn supernovae (SNe), SN 2018jmt and SN 2019cj. Their light curves have rise times of about 10 days, reaching an absolute peak magnitude of $M_g$(SN 2018jmt) = $-$19.07 $\pm$ 0.37 and $M_V$(SN 2019cj) = $-$18.94 $\pm$ 0.19 mag, respectively. The early-time spectra of SN 2018jmt are dominated by a blue continuum, accompanied by narrow (6… ▽ More We present optical and near-infrared observations of two Type Ibn supernovae (SNe), SN 2018jmt and SN 2019cj. Their light curves have rise times of about 10 days, reaching an absolute peak magnitude of $M_g$(SN 2018jmt) = $-$19.07 $\pm$ 0.37 and $M_V$(SN 2019cj) = $-$18.94 $\pm$ 0.19 mag, respectively. The early-time spectra of SN 2018jmt are dominated by a blue continuum, accompanied by narrow (600$-$1000 km~s$^{-1}$) He I lines with P-Cygni profile. At later epochs, the spectra become more similar to those of the prototypical SN Ibn 2006jc. At early phases, the spectra of SN 2019cj show flash ionisation emission lines of C III, N III and He II superposed on a blue continuum. These features disappear after a few days, and then the spectra of SN 2019cj evolve similarly to those of SN 2018jmt. The spectra indicate that the two SNe exploded within a He-rich circumstellar medium (CSM) lost by the progenitors a short time before the explosion. We model the light curves of the two SNe Ibn to constrain the progenitor and the explosion parameters. The ejecta masses are consistent with either that expected for a canonical SN Ib ($\sim$ 2 M$_{\odot}$) or those from a massive WR star ($>$ $\sim$ 4 M$_{\odot}$), with the kinetic energy on the order of $10^{51}$ erg. The lower limit on the ejecta mass ($>$ $\sim$ 2 M$_{\odot}$) argues against a scenario involving a relatively low-mass progenitor (e.g., $M_{ZAMS}$ $\sim$ 10 M$_{\odot}$). We set a conservative upper limit of $\sim$0.1 M$_{\odot}$ for the $^{56}$Ni masses in both SNe. From the light curve modelling, we determine a two-zone CSM distribution, with an inner, flat CSM component, and an outer CSM with a steeper density profile. The physical properties of SN 2018jmt and SN 2019cj are consistent with those expected from the core collapse of relatively massive, stripped-envelope (SE) stars. △ Less

Submitted 22 August, 2024; originally announced August 2024.

Comments: 28 pages, 19 figures, Accepted for publication in Astronomy & Astrophysics

Journal ref: A&A 691, A156 (2024)

Various Features of the X-class White-light Flares in Super Active Region NOAA 13664

Authors: Ying Li, Xiaofeng Liu, Zhichen Jing, Wei Chen, Qiao Li, Yang Su, De-Chao Song, M. D. Ding, Li Feng, Hui Li, Weiqun Gan

Abstract: Super active region NOAA 13664 produced 12 X-class flares (including the largest one, an occulted X8.7 flare, in solar cycle 25 so far) during 2024 May 8-15 and 11 of them are identified as white-light flares. Here we present various features of these X-class white-light flares observed by the White-light Solar Telescope (WST) on board the Advanced Space-based Solar Observatory and the Helioseismi… ▽ More Super active region NOAA 13664 produced 12 X-class flares (including the largest one, an occulted X8.7 flare, in solar cycle 25 so far) during 2024 May 8-15 and 11 of them are identified as white-light flares. Here we present various features of these X-class white-light flares observed by the White-light Solar Telescope (WST) on board the Advanced Space-based Solar Observatory and the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory. It is found that both the white-light emissions at WST 3600 Å (Balmer continuum) and HMI 6173 Å (Paschen continuum) show up in different regions of the sunspot group in these flares, including outside the sunspots and within the penumbra and umbra of the sunspots. They exhibit a point-, ribbon-, loop-, or ejecta-like shape, which can come from flare ribbons (or footpoints), flare loops, and plasma ejecta depending on the perspective view. The white-light duration and relative enhancement are measured and both parameters for 3600 Å emission have greater values than those for 6173 Å emission. It is also found that these white-light emissions are cospatial well with the hard X-ray (HXR) sources in the on-disk flares but have some offsets with the HXR emissions in the off-limb flares. In addition, it is interesting that the 3600 and 6173 Å emissions show different correlations with the peak HXR fluxes, with the former one more sensitive to the HXR emission. All these greatly help us understand the white-light flares of a large magnitude from a super active region on the Sun and also provide important insights into superflares on Sun-like stars. △ Less

Submitted 11 August, 2024; originally announced August 2024.

Comments: Accepted for publication in ApJL. Any comments are welcome

A new quantization scheme of black holes in effective loop quantum gravity

Authors: Wen-Cong Gan, Anzhong Wang

Abstract: Loop quantum cosmology has achieved great successes, in which the polymerization plays a crucial role. In particular, the phase-space-variable dependent polymerization turns out to be the unique one that leads to consistent quantization of the homogeneous and isotropic universe. However, when applying the same scheme to the quantization of black holes, it meets resistances, when the Kantowski-Sach… ▽ More Loop quantum cosmology has achieved great successes, in which the polymerization plays a crucial role. In particular, the phase-space-variable dependent polymerization turns out to be the unique one that leads to consistent quantization of the homogeneous and isotropic universe. However, when applying the same scheme to the quantization of black holes, it meets resistances, when the Kantowski-Sachs (KS) gauge is adopted. In this paper, we continue to study the quantum effects of the polymerization near the location that a classical black hole horizon used to be, from the point of view of effective loop quantum gravity in the KS gauge. In particular, we find a phase-space-variable dependent polymerization scheme that leads to negligible quantum effects near the location of the classical black hole horizon, but significantly alters the spacetime structure near the origin, so that the classical singularity is finally replaced by a finite and regular transition surface. The final geodesically-complete spacetime consists of the regular transition surface that connects a black hole in one side and an anti-trapped region in the other side. In the anti-trapped region, no white hole horizons are found and the spacetime is extended to infinity, at which the geometric radius of the two-spheres becomes infinitely large. △ Less

Submitted 8 August, 2024; v1 submitted 8 August, 2024; originally announced August 2024.

Comments: revtex4-2, 17 figures, and no tables; v2: typos corrected

Journal ref: Phys.Rev.D 111 (2025) 2, 026017

Inflight Performance and Calibrations of the Lyman-alpha Solar Telescope on board the Advanced Space-based Solar Observatory

Authors: Bo Chen, Li Feng, Guang Zhang, Hui Li, Lingping He, Kefei Song, Quanfeng Guo, Ying Li, Yu Huang, Jingwei Li, Jie Zhao, Jianchao Xue, Gen Li, Guanglu Shi, Dechao Song, Lei Lu, Beili Ying, Haifeng Wang, Shuang Dai, Xiaodong Wang, Shilei Mao, Peng Wang, Kun Wu, Shuai Ren, Liang Sun , et al. (18 additional authors not shown)

Abstract: The Lyman-alpha Solar Telescope (LST) on board the Advanced Space-based Solar Observatory (ASO-S) is the first payload to image the full solar disk and the solar corona in both white-light (WL) and ultraviolet (UV) H I Lya, extending up to 2.5 solar radii (Rs). Since the launch of the ASO-S on 9 October 2022, LST has captured various significant solar activities including flares, prominences, coro… ▽ More The Lyman-alpha Solar Telescope (LST) on board the Advanced Space-based Solar Observatory (ASO-S) is the first payload to image the full solar disk and the solar corona in both white-light (WL) and ultraviolet (UV) H I Lya, extending up to 2.5 solar radii (Rs). Since the launch of the ASO-S on 9 October 2022, LST has captured various significant solar activities including flares, prominences, coronal mass ejections (CMEs). LST covers different passbands of 121.6 nm, 360 nm and 700 nm. The Lya Solar Disk Imager (SDI) has a field of view (FOV) of 38.4 arcmin and a spatial resolution of around 9.5 arcsec, while the White-Light Solar Telescope (WST) has a FOV of 38.43 arcmin and a spatial resolution of around 3.0 arcsec. The FOV of the Lya Solar Corona Imager (SCI) reaches 81.1 arcmin and its spatial resolution is 4.3 arcsec. The stray-light level in the 700 nm waveband is about 7.8e-6 MSB (mean solar brightness) at 1.1 Rs and 7.6e-7 MSB at 2.5 Rs, and in the Lya waveband it is around 4.3e-3 MSB at 1.1 Rs and 4.1e-4 MSB at 2.5 Rs. This article will detail the results from on-orbit tests and calibrations. △ Less

Submitted 4 August, 2024; originally announced August 2024.

Comments: Solar Physics (ASO-S mission topical collection), accepted

Asymmetric Hard X-ray Radiation of Two Ribbons in a Thermal-Dominated C-Class Flare

Authors: Guanglu Shi, Li Feng, Jun Chen, Beili Ying, Shuting Li, Qiao Li, Hui Li, Ying Li, Kaifan Ji, Yu Huang, Weiqun Gan, the LST team

Abstract: The asymmetry in hard X-ray (HXR) emission at the footpoints (FPs) of flare loops is a ubiquitous feature closely associated with nonthermal electron transport. We analyze the asymmetric HXR radiation at two flare ribbons which is thermal-dominated during a long-duration C4.4 flare that occurred on March 20, 2023, combining multi-view and multi-waveband observations from the ASO-S, SolO, and SDO s… ▽ More The asymmetry in hard X-ray (HXR) emission at the footpoints (FPs) of flare loops is a ubiquitous feature closely associated with nonthermal electron transport. We analyze the asymmetric HXR radiation at two flare ribbons which is thermal-dominated during a long-duration C4.4 flare that occurred on March 20, 2023, combining multi-view and multi-waveband observations from the ASO-S, SolO, and SDO spacecraft. We find that the H I Ly$α$ emission captures similar features to the He II $λ$304 in both light curve and spatio-temporal evolution of a pair of conjugate flare ribbons. The spectra and imaging analysis of the HXR emission, detected by STIX in 4-18 keV, reveal that the two-ribbon flare radiation is thermal dominated by over 95%, and the radiation source mainly concentrates on the northern ribbon, leading to an asymmetric distribution. To understand the underlying reasons for the HXR radiation asymmetry, we extrapolate the magnetic field within the active region using the NLFFF model. For 78% of the magnetic field lines starting from the northern flare ribbon, their lengths from the loop-tops (LTs) to the northern FPs are shorter than those to the southern FPs. For 62% of the field lines, their magnetic field strengths at the southern FPs exceed those at the northern FPs. In addition, considering the larger density, $\approx1.0\times10^{10}$ cm$^{-3}$, of the low-lying flare loops (< 32 Mm), we find the shorter path from the LT to the northern FP enables more electrons to reach the northern FP more easily after collisions with the surrounding plasma. Therefore, in this thermal-dominated C-class flare, the asymmetric location of the flare LT relative to its two FPs plays a dominant role in the HXR radiation asymmetry, while such asymmetry is also slightly influenced by the magnetic mirror effect resulting in larger HXR radiation at the FPs with weaker magnetic strength. △ Less

Submitted 17 July, 2024; originally announced July 2024.

Comments: 21 pages, 7 figures, accepted by Solar Physics. Comments welcome

Association between a Failed Prominence Eruption and the Drainage of Mass from Another Prominence

Authors: Jianchao Xue, Li Feng, Hui Li, Ping Zhang, Jun Chen, Guanglu Shi, Kaifan Ji, Ye Qiu, Chuan Li, Lei Lu, Beili Ying, Ying Li, Yu Huang, Youping Li, Jingwei Li, Jie Zhao, Dechao Song, Shuting Li, Zhengyuan Tian, Yingna Su, Qingmin Zhang, Yunyi Ge, Jiahui Shan, Qiao Li, Gen Li , et al. (9 additional authors not shown)

Abstract: Sympathetic eruptions of solar prominences have been studied for decades, however, it is usually difficult to identify their causal links. Here we present two failed prominence eruptions on 26 October 2022 and explore their connections. Using stereoscopic observations, the south prominence (PRO-S) erupts with untwisting motions, flare ribbons occur underneath, and new connections are formed during… ▽ More Sympathetic eruptions of solar prominences have been studied for decades, however, it is usually difficult to identify their causal links. Here we present two failed prominence eruptions on 26 October 2022 and explore their connections. Using stereoscopic observations, the south prominence (PRO-S) erupts with untwisting motions, flare ribbons occur underneath, and new connections are formed during the eruption. The north prominence (PRO-N) rises up along with PRO-S, and its upper part disappears due to catastrophic mass draining along an elongated structure after PRO-S failed eruption. We suggest that the eruption of PRO-S initiates due to a kink instability, further rises up, and fails to erupt due to reconnection with surrounding fields. The elongated structure connecting PRO-N overlies PRO-S, which causes the rising up of PRO-N along with PRO-S and mass drainage after PRO-S eruption. This study suggests that a prominence may end its life through mass drainage forced by an eruption underneath. △ Less

Submitted 20 June, 2024; v1 submitted 17 June, 2024; originally announced June 2024.

Comments: 15 pages, 7 figures, has been accepted by Solar Physics

Parameter effects on the total intensity of H I Lyα line for a modelled coronal mass ejection and its driven shock

Authors: Beili Ying, Guanglu Shi, Li Feng, Lei Lu, Jianchao Xue, Shuting Li, Weiqun Gan, Hui Li

Abstract: The combination of the H I Lyα (121.6 nm) line formation mechanism with ultraviolet (UV) Lyα and white-light (WL) observations provides an effective method for determining the electron temperature of coronal mass ejections (CMEs). A key to ensuring the accuracy of this diagnostic technique is the precise calculation of theoretical Lyα intensities. This study performs a modelled CME and its driven… ▽ More The combination of the H I Lyα (121.6 nm) line formation mechanism with ultraviolet (UV) Lyα and white-light (WL) observations provides an effective method for determining the electron temperature of coronal mass ejections (CMEs). A key to ensuring the accuracy of this diagnostic technique is the precise calculation of theoretical Lyα intensities. This study performs a modelled CME and its driven shock via the 3D MHD simulation. We generate synthetic UV and WL images of the CME and shock to quantify the impact of different assumptions on theoretical Lyα intensities, such as the incident intensity of the Lyα line (Idisk), the geometric scattering function (p(θ)), and the kinetic temperature (Tn) assumed to be equal to the proton (Tp) or electron (Te) temperatures. By comparing differences of the Lyα intensities under these assumptions, we find that: (1) Using the uniform or Carrington maps of the disk Lyα emission underestimates the corona Lyα intensity (< 10%) compared to the synchronic map, except for a slight overestimate (< 4%) in the partial CME core. The Carrington map yields lower uncertainties than the uniform disk. (2) The geometric scattering process has a minor impact on the Lyα intensity, with a maximum relative uncertainty of < 5%. The Lyα intensity is underestimated for the most part but overestimated in the CME core. (3) Compared to the assumption Tn = Tp, using Tn = Te leads to more complex relative uncertainties in CME Lyα intensity. The CME core and void are both overestimated, with the maximum uncertainty in the core exceeding 50% and the void remaining below 35%. In the CME front, both over- and under-estimates exist with relative uncertainties of < 35%. The electron temperature assumption has a smaller impact on the shock, with an underestimated relative uncertainty of less than 20%. △ Less

Submitted 17 June, 2024; originally announced June 2024.

Comments: 22 pages, 9 figures, accepted by Solar Physics

High-resolution Observation of Blowout Jets Regulated by Sunspot Rotation

Authors: Tingyu Gou, Rui Liu, Yang Su, Astrid M. Veronig, Hanya Pan, Runbin Luo, Weiqun Gan

Abstract: Coronal jets are believed to be the miniature version of large-scale solar eruptions. In particular, the eruption of a mini-filament inside the base arch is suggested to be the trigger and even driver of blowout jets. Here we propose an alternative triggering mechanism, based on high-resolution H-alpha observations of a blowout jet associated with a mini-filament and an M1.2-class flare. The mini-… ▽ More Coronal jets are believed to be the miniature version of large-scale solar eruptions. In particular, the eruption of a mini-filament inside the base arch is suggested to be the trigger and even driver of blowout jets. Here we propose an alternative triggering mechanism, based on high-resolution H-alpha observations of a blowout jet associated with a mini-filament and an M1.2-class flare. The mini-filament remains largely stationary during the blowout jet, except that it is straddled by flare loops connecting two flare ribbons, indicating that the magnetic arcade embedding the mini-filament has been torn into two parts, with the upper part escaping with the blowout jet. In the wake of the flare, the southern end of the mini-filament fans out like neighboring fibrils, indicative of mass and field exchanges between the mini-filament and the fibrils. The blowout jet is preceded by a standard jet. With H-alpha fibrils moving toward the single-strand spire in a sweeping fashion, the standard jet transitions to the blowout jet. The similar pattern of standard-to-blowout jet transition occurs in an earlier C-class flare before the mini-filament forms. The spiraling morphology and sweeping direction of these fibrils are suggestive of their footpoints being dragged by the leading sunspot that undergoes clockwise rotation for over two days. Soon after the sunspot rotation reaches a peak angular speed as fast as 10 deg/hr, the dormant active region becomes flare-productive, and the mini-filament forms through the interaction of moving magnetic features from the rotating sunspot with satellite spots/pores. Hence, we suggest that the sunspot rotation plays a key role in building up free energy for flares and jets and in triggering blowout jets by inducing sweeping motions of fibrils. △ Less

Submitted 4 June, 2024; originally announced June 2024.

Comments: 16 pages, 10 figures, accepted in Solar Physics

Refinement of global coronal and interplanetary magnetic field extrapolations constrained by remote-sensing and in-situ observations at the solar minimum

Authors: Guanglu Shi, Li Feng, Beili Ying, Shuting Li, Weiqun Gan

Abstract: Solar magnetic fields are closely related to various physical phenomena on the sun, which can be extrapolated with different models from photospheric magnetograms. However, the Open Flux Problem (OFP), the underestimation of the magnetic field derived from the extrapolated model, is still unsolved. To minimize the impact of the OFP, we propose three evaluation parameters to quantitatively evaluate… ▽ More Solar magnetic fields are closely related to various physical phenomena on the sun, which can be extrapolated with different models from photospheric magnetograms. However, the Open Flux Problem (OFP), the underestimation of the magnetic field derived from the extrapolated model, is still unsolved. To minimize the impact of the OFP, we propose three evaluation parameters to quantitatively evaluate magnetic field models and determine the optimal free parameters in the models by constraining the coronal magnetic fields (CMFs) and the interplanetary magnetic fields (IMFs) with real observations. Although the OFP still exists, we find that magnetic field lines traced from the coronal models effectively capture the intricate topological configurations observed in the corona, including streamers and plumes. The OFP is lessened by using the HMI synoptic map instead of the GONG daily synoptic maps, and the PFSS+PFCS model instead of the CSSS model. For Carrington Rotation (CR) 2231 at the solar minimum, we suggest that the optimal parameters for the PFSS+PFCS model are $R_{\mathrm{ss}} = 2.2-2.5\ R_{\mathrm{sun}}$ and $R_{\mathrm{scs}} = 10.5-14.0\ R_{\mathrm{sun}}$, as well as for the CSSS model are $R_{\mathrm{cs}} = 2.0 - 2.4\ R_{\mathrm{sun}}$, $R_{\mathrm{ss}} = 11.0 - 14.7\ R_{\mathrm{sun}}$ and $a = 1.0\ R_{\mathrm{sun}}$. Despite the IMFs at 1 AU being consistent with the measurements by artificially increasing the polar magnetic fields, the IMFs near the sun are still underestimated. The OFP might be advanced by improving the accuracy of both the weak magnetic fields and polar magnetic fields, especially considering magnetic activities arising from interplanetary physical processes. △ Less

Submitted 28 May, 2024; originally announced May 2024.

Comments: 21 pages, 15 figures, accepted for publication in ApJ

The Energy Sources, the Physical Properties, and the Mass-loss History of SN 2017dio

Authors: Deng-Wang Shi, Shan-Qin Wang, Wen-Pei Gan, En-Wei Liang

Abstract: We study the energy sources, the physical properties of the ejecta and the circumstellar medium (CSM), as well as the mass-loss history of the progenitor of SN 2017dio which is a broad-lined Ic (Ic-BL) supernova (SN) having unusual light curves (LCs) and signatures of hydrogen-rich CSM in its early spectrum. We find that the temperature of SN 2017dio began to increase linearly about 20 days after… ▽ More We study the energy sources, the physical properties of the ejecta and the circumstellar medium (CSM), as well as the mass-loss history of the progenitor of SN 2017dio which is a broad-lined Ic (Ic-BL) supernova (SN) having unusual light curves (LCs) and signatures of hydrogen-rich CSM in its early spectrum. We find that the temperature of SN 2017dio began to increase linearly about 20 days after the explosion. We use the $^{56}$Ni plus the ejecta-CSM interaction (CSI) model to fit the LCs of SN 2017dio, finding that the masses of the ejecta, the $^{56}$Ni, and the CSM are $\sim$ 12.41 M$_\odot$, $\sim$ 0.17 M$_\odot$, and $\sim$ 5.82 M$_\odot$, respectively. The early-time photosphere velocity and the kinetic energy of the SN are respectively {$\sim$ 1.89 $\times 10^4$ km s$^{-1}$} and $\sim$ 2.66 $\times 10^{52}$ erg, which are respectively comparable to those of SNe Ic-BL and hypernovae (HNe). We suggest that the CSM of SN 2017dio might be {from an luminous-blue-variable-like outburst or} pulsational pair instability $\sim$ 1.2$-$11.4 yr prior to the SN explosion{, or binary mass transfer}. {Moreover,} we find that its ejecta mass is larger than those of many SNe Ic-BL, and that its $^{56}$Ni mass ($M_{\rm Ni}$) is approximately equal to the mean (or median) value of $M_{\rm Ni}$ of SNe Ic-BL in the literature, but lower than $M_{\rm Ni}$ of prototype HNe (e.g., SN 1998bw and SN 2003dh). △ Less

Submitted 13 May, 2024; originally announced May 2024.

Comments: Accepted for publication in ApJ, 17 pages, 4 figures, 3 tables

Spectral and Imaging Observations of a C2.3 White-Light Flare from the Advanced Space-Based Solar Observatory (ASO-S) and the Chinese H$α$ Solar Explorer (CHASE)

Authors: Qiao Li, Ying Li, Yang Su, Dechao Song, Hui Li, Li Feng, Yu Huang, Youping Li, Jingwei Li, Jie Zhao, Lei Lu, Beili Ying, Jianchao Xue, Ping Zhang, Jun Tian, Xiaofeng Liu, Gen Li, Zhichen Jing, Shuting Li, Guanglu Shi, Zhengyuan Tian, Wei Chen, Yingna Su, Qingmin Zhang, Dong Li , et al. (5 additional authors not shown)

Abstract: Solar white-light flares are characterized by an enhancement in the optical continuum, which are usually large flares (say X- and M-class flares). Here we report a small C2.3 white-light flare (SOL2022-12-20T04:10) observed by the \emph{Advanced Space-based Solar Observatory} and the \emph{Chinese H$α$ Solar Explorer}. This flare exhibits an increase of $\approx$6.4\% in the photospheric Fe \texts… ▽ More Solar white-light flares are characterized by an enhancement in the optical continuum, which are usually large flares (say X- and M-class flares). Here we report a small C2.3 white-light flare (SOL2022-12-20T04:10) observed by the \emph{Advanced Space-based Solar Observatory} and the \emph{Chinese H$α$ Solar Explorer}. This flare exhibits an increase of $\approx$6.4\% in the photospheric Fe \textsc{i} line at 6569.2\,Å and {$\approx$3.2\%} in the nearby continuum. The continuum at 3600\,Å also shows an enhancement of $\approx$4.7\%. The white-light brightening kernels are mainly located at the flare ribbons and co-spatial with nonthermal hard X-ray sources, which implies that the enhanced white-light emissions are related to nonthermal electron-beam heating. At the brightening kernels, the Fe \textsc{i} line displays an absorption profile that has a good Gaussian shape, with a redshift up to $\approx$1.7 km s$^{-1}$, while the H$α$ line shows an emission profile though having a central reversal. The H$α$ line profile also shows a red or blue asymmetry caused by plasma flows with a velocity of several to tens of km s$^{-1}$. It is interesting to find that the H$α$ asymmetry is opposite at the conjugate footpoints. It is also found that the CHASE continuum increase seems to be related to the change of photospheric magnetic field. Our study provides comprehensive characteristics of a small white-light flare that help understand the energy release process of white-light flares. △ Less

Submitted 2 May, 2024; originally announced May 2024.

Comments: 23 pages, 6 figures, accepted by Solar Physics

AT2023lli: A Tidal Disruption Event with Prominent Optical Early Bump and Delayed Episodic X-ray Emission

Authors: Shifeng Huang, Ning Jiang, Jiazheng Zhu, Yibo Wang, Tinggui Wang, Shan-Qin Wang, Wen-Pei Gan, En-Wei Liang, Yu-Jing Qin, Zheyu Lin, Lin-Na Xu, Min-Xuan Cai, Ji-An Jiang, Xu Kong, Jiaxun Li, Long Li, Jian-Guo Wang, Ze-Lin Xu, Yongquan Xue, Ye-Fei Yuan, Jingquan Cheng, Lulu Fan, Jie Gao, Lei Hu, Weida Hu , et al. (20 additional authors not shown)

Abstract: High-cadence, multiwavelength observations have continuously revealed the diversity of tidal disruption events (TDEs), thus greatly advancing our knowledge and understanding of TDEs. In this work, we conducted an intensive optical-UV and X-ray follow-up campaign of TDE AT2023lli, and found a remarkable month-long bump in its UV/optical light curve nearly two months prior to maximum brightness. The… ▽ More High-cadence, multiwavelength observations have continuously revealed the diversity of tidal disruption events (TDEs), thus greatly advancing our knowledge and understanding of TDEs. In this work, we conducted an intensive optical-UV and X-ray follow-up campaign of TDE AT2023lli, and found a remarkable month-long bump in its UV/optical light curve nearly two months prior to maximum brightness. The bump represents the longest separation time from the main peak among known TDEs to date. The main UV/optical outburst declines as $t^{-4.10}$, making it one of the fastest decaying optically selected TDEs. Furthermore, we detected sporadic X-ray emission 30 days after the UV/optical peak, accompanied by a reduction in the period of inactivity. It is proposed that the UV/optical bump could be caused by the self-intersection of the stream debris, whereas the primary peak is generated by the reprocessed emission of the accretion process. In addition, our results suggest that episodic X-ray radiation during the initial phase of decline may be due to the patched obscurer surrounding the accretion disk, a phenomenon associated with the inhomogeneous reprocessing process. The double TDE scenario, in which two stars are disrupted in sequence, is also a possible explanation for producing the observed early bump and main peak. We anticipate that the multicolor light curves of TDEs, especially in the very early stages, and the underlying physics can be better understood in the near future with the assistance of dedicated surveys such as the deep high-cadence survey of the 2.5-meter Wide Field Survey Telescope (WFST). △ Less

Submitted 26 March, 2024; v1 submitted 3 March, 2024; originally announced March 2024.

Comments: 14 pages, 8 figures,accepted for publication by ApJL

The White-light Emissions in Two X-class Flares Observed by ASO-S and CHASE

Authors: Ying Li, Zhichen Jing, De-Chao Song, Qiao Li, Jun Tian, Xiaofeng Liu, Ya Wang, M. D. Ding, Andrea Francesco Battaglia, Li Feng, Hui Li, Weiqun Gan

Abstract: The white-light continuum emissions in solar flares (i.e., white-light flares) are usually observed on the solar disk but, in a few cases, off the limb. Here we present on-disk as well as off-limb continuum emissions at 3600 Å (in the Balmer continuum) in an X2.1 flare (SOL2023-03-03T17:52) and an X1.5 flare (SOL2023-08-07T20:46), respectively, observed by the White-light Solar Telescope (WST) on… ▽ More The white-light continuum emissions in solar flares (i.e., white-light flares) are usually observed on the solar disk but, in a few cases, off the limb. Here we present on-disk as well as off-limb continuum emissions at 3600 Å (in the Balmer continuum) in an X2.1 flare (SOL2023-03-03T17:52) and an X1.5 flare (SOL2023-08-07T20:46), respectively, observed by the White-light Solar Telescope (WST) on the Advanced Space-based Solar Observatory (ASO-S). These continuum emissions are seen at the ribbons for the X2.1 flare and on loops during the X1.5 event, in which the latter also appears in the decay phase. These emissions also show up in the pseudo-continuum images at Fe I λ6173 from the Helioseismic and Magnetic Imager (HMI) on the Solar Dynamics Observatory (SDO). In addition, the ribbon sources in the X2.1 flare exhibit significant enhancements in the Fe I line at 6569.2 Å and the nearby continuum observed by the Chinese Hα Solar Explorer (CHASE). It is found that the on-disk continuum emissions in the X2.1 flare are related to a nonthermal electron-beam heating either directly or indirectly, while the off-limb emissions in the X1.5 flare are associated with thermal plasma cooling or due to Thomson scattering. These comprehensive continuum observations can provide good constraints on flare energy deposition models, which helps well understand the physical mechanism of white-light flares. △ Less

Submitted 11 February, 2024; originally announced February 2024.

Comments: 13 pages, 1 table, 4 figures, accepted for publication in ApJL

A Statistical Study of Solar White-Light Flares Observed by the White-light Solar Telescope of the Lyman-alpha Solar Telescope on the Advanced Space-based Solar Observatory (ASO-S/LST/WST) at 360 nm

Authors: Zhichen Jing, Ying Li, Li Feng, Hui Li, Yu Huang, Youping Li, Yang Su, Wei Chen, Jun Tian, Dechao Song, Jingwei Li, Jianchao Xue, Jie Zhao, Lei Lu, Beili Ying, Ping Zhang, Yingna Su, Qingmin Zhang, Dong Li, Yunyi Ge, Shuting Li, Qiao Li, Gen Li, Xiaofeng Liu, Guanglu Shi , et al. (4 additional authors not shown)

Abstract: Solar white-light flares (WLFs) are those accompanied by brightenings in the optical continuum or integrated light. The White-light Solar Telescope (WST), as an instrument of the Lyman-alpha Solar Telescope (LST) on the Advanced Space-based Solar Observatory (ASO-S), provides continuous solar full-disk images at 360 nm, which can be used to study WLFs. We analyze 205 major flares above M1.0 from O… ▽ More Solar white-light flares (WLFs) are those accompanied by brightenings in the optical continuum or integrated light. The White-light Solar Telescope (WST), as an instrument of the Lyman-alpha Solar Telescope (LST) on the Advanced Space-based Solar Observatory (ASO-S), provides continuous solar full-disk images at 360 nm, which can be used to study WLFs. We analyze 205 major flares above M1.0 from October 2022 to May 2023 and identify 49 WLFs at 360 nm from WST observations, i.e. with an occurrence rate of 23.9%. The percentages of WLFs for M1 - M4 (31 out of 180), M5 - M9 (11 out of 18), and above X1 (7 for all) flares are 17.2%, 61.1%, and 100%, respectively, namely the larger the flares, the more likely they are WLFs at 360 nm. We further analyze 39 WLFs among the identified WLFs and investigate their properties such as white-light enhancement, duration, and brightening area. It is found that the relative enhancement of the white-light emission at 360 nm is mostly (>90%) less than 30% and the mean enhancement is 19.4%. The WLFs' duration at 360 nm is mostly (>80%) less than 20 minutes and its mean is 10.3 minutes. The brightening area at 360 nm is mostly (>75%) less than 500 arcsecond2 and the median value is 225. We find that there exist good correlations between the white-light enhancement/duration/area and the peak soft X-ray (SXR) flux of the flare, with correlation coefficients of 0.68, 0.58, and 0.80, respectively. In addition, the white-light emission in most WLFs peaks around the same time as the temporal derivative of SXR flux as well as the hard X-ray emission at 20 - 50 keV, indicative of Neupert effect. It is also found that the limb WLFs are more likely to have a greater enhancement, which is consistent with numerical simulations. △ Less

Submitted 14 January, 2024; originally announced January 2024.

Partial Eruption of Solar Filaments. I. Configuration and Formation of Double-decker Filaments

Authors: Yijun Hou, Chuan Li, Ting Li, Jiangtao Su, Ye Qiu, Shuhong Yang, Liheng Yang, Leping Li, Yilin Guo, Zhengyong Hou, Qiao Song, Xianyong Bai, Guiping Zhou, Mingde Ding, Weiqun Gan, Yuanyong Deng

Abstract: Partial eruptions of solar filaments are the typical representative of solar eruptive behavior diversity. Here we investigate a typical filament partial eruption event and present integrated evidence for configuration of the pre-eruption filament and its formation. The CHASE H$α$ observations reveal structured Doppler velocity distribution within the pre-eruption filament, where distinct redshift… ▽ More Partial eruptions of solar filaments are the typical representative of solar eruptive behavior diversity. Here we investigate a typical filament partial eruption event and present integrated evidence for configuration of the pre-eruption filament and its formation. The CHASE H$α$ observations reveal structured Doppler velocity distribution within the pre-eruption filament, where distinct redshift only appeared in the east narrow part of the south filament region and then disappeared after the partial eruption while the north part dominated by blueshift remained. Combining the SDO, ASO-S observations, and NLFFF modeling results, we verify that there were two independent material flow systems within the pre-flare filament, whose magnetic topology is a special double-decker configuration consisting of two magnetic flux ropes (MFRs) with opposite magnetic twist. During the formation of this filament system, continuous magnetic flux cancellation and footpoint motion were observed around its north end. Therefore, we propose a new double-decker formation scenario that the two MFRs composing such double-decker configuration originated from two magnetic systems with different initial connections and opposite magnetic twist. Subsequent magnetic reconnection with surrounding newly-emerging fields resulted in the motion of footpoint of the upper MFR to the region around footpoint of the lower MFR, thus leading to eventual formation of the double-decker configuration consisting of two MFRs with similar footpoints but opposite signs of magnetic twist. These results provide a potential way to determine unambiguously the progenitor configuration of a partial-eruptive filament and reveal a special type of double-decker MFR configuration and a new double-decker formation scenario. △ Less

Submitted 1 November, 2023; originally announced November 2023.

Comments: 16 pages, 8 figures, 1 table, accepted for publication in ApJ as part of the Focus Issue "Early results from the Chinese Ha Solar Explorer (CHASE)"

Nonexistence of quantum black and white hole horizons in an improved dynamic approach

Authors: Wen-Cong Gan, Xiao-Mei Kuang, Zhen-Hao Yang, Yungui Gong, Anzhong Wang, Bin Wang

Abstract: In this paper, we study the quantum geometric effects near the locations where classical black hole horizons used to appear in Einstein's classical theory, within the framework of an improved dynamic approach, in which the internal region of a black hole is modeled by the Kantowski-Sachs (KS) spacetime and the two polymerization parameters are functions of the phase space variables. Our detailed a… ▽ More In this paper, we study the quantum geometric effects near the locations where classical black hole horizons used to appear in Einstein's classical theory, within the framework of an improved dynamic approach, in which the internal region of a black hole is modeled by the Kantowski-Sachs (KS) spacetime and the two polymerization parameters are functions of the phase space variables. Our detailed analysis shows that the effects are so strong that black and white hole horizons of the effective quantum theory do not exist at all and instead are replaced by transition surfaces, across which the metric coefficients and their inverses are smooth and remain finite, as are the corresponding curvatures, including the Kretschmann scalar. These surfaces always separate trapped regions from anti-trapped regions. The number of such surfaces is infinite, so the corresponding KS spacetimes become geodesically complete, and no black and white hole-like structures exist in this scheme. △ Less

Submitted 31 July, 2024; v1 submitted 29 December, 2022; originally announced December 2022.

Comments: revtex4-2, 6 figures, and two tables, v2: typos corrected, references added, v3: Additional analyses were provided, including new references and figures, while the conclusions remain the same, v4: to appear in SCIENCE CHINA Physics, Mechanics & Astronomy, v5: published version in SCIENCE CHINA Physics, Mechanics & Astronomy

Journal ref: Sci.China Phys.Mech.Astron. 67 (2024) 8, 280411

SN 2018gk Revisited: the Photosphere, the Central Engine, And the Putative Dust

Authors: Tao Wang, Shan-Qin Wang, Wen-Pei Gan, Long Li

Abstract: In this paper, we perform a comprehensive study for the physical properties of SN 2018gk which is a luminous type IIb supernova (SN). We find that the early-time photospheric velocity vary from a larger value to a smaller value before the photosphere reach a temperature floor. We generalize the photosphere modulus and fit the multi-band light curves (LCs) of SN 2018gk. We find that the $^{56}$Ni m… ▽ More In this paper, we perform a comprehensive study for the physical properties of SN 2018gk which is a luminous type IIb supernova (SN). We find that the early-time photospheric velocity vary from a larger value to a smaller value before the photosphere reach a temperature floor. We generalize the photosphere modulus and fit the multi-band light curves (LCs) of SN 2018gk. We find that the $^{56}$Ni mass model require $\sim0.90$ M$_\odot$ of $^{56}$Ni which is larger than the derived ejecta mass ($\sim0.10$ M$_\odot$). Alternatively, we use the magnetar plus $^{56}$Ni and the fallback plus $^{56}$Ni models to fit the LCs of SN 2018gk, finding that the two models can fit the LCs. We favor the magnetar plus $^{56}$Ni since the parameters are rather reasonable ($M_{\rm ej} =1.65$ M$_\odot$, $M_{\rm Ni}=0.05$ M$_\odot$ which is smaller than the upper limit of the value of the $^{56}$Ni mass can by synthesized by the neutrino-powered core collapse SNe $B=6.52\times10^{14}$ G which is comparable to those of luminous and superluminous SNe studied in the literature, and $P_0=10.42$ ms which is comparable to those of luminous SNe), while the validity of the fallback plus $^{56}$Ni model depends on the accretion efficiency ($η$). Therefore, we suggest that SN 2018gk might be a SN IIb mainly powered by a central engine. Finally, we confirm the NIR excesses of the spectral energy distributions (SEDs) of SN 2018gk at some epochs and constrain the physical properties of the putative dust using the blackbody plus dust emission model. △ Less

Submitted 7 March, 2023; v1 submitted 29 November, 2022; originally announced November 2022.

Comments: 26 pages, 11 figures, 5 tables, Accepted for publication in ApJ

Is there a Dynamic Difference between Stealthy and Standard CMEs?

Authors: Beili Ying, Alessandro Bemporad, Li Feng, Nariaki V. Nitta, Weiqun Gan

Abstract: Stealthy Coronal Mass Ejections (CMEs), lacking low coronal signatures, may result in significant geomagnetic storms. However, the mechanism of stealthy CMEs is still highly debated. In this work, we investigate whether there are differences between the stealthy and standard CMEs in terms of their dynamic behaviors. Seven stealthy and eight standard CMEs with slow speeds are selected. We calculate… ▽ More Stealthy Coronal Mass Ejections (CMEs), lacking low coronal signatures, may result in significant geomagnetic storms. However, the mechanism of stealthy CMEs is still highly debated. In this work, we investigate whether there are differences between the stealthy and standard CMEs in terms of their dynamic behaviors. Seven stealthy and eight standard CMEs with slow speeds are selected. We calculate two-dimensional speed distributions of CMEs based on the cross-correlation method, rather than the unidimensional speed, and further obtain more accurate distributions and evolution of CME mechanical energies. Then we derive the CME driving powers and correlate them with CME parameters (total mass, average speed, and acceleration) for standard and stealthy CMEs. Besides, we study the forces that drive CMEs, namely, the Lorentz force, gravitational force, and drag force due to the ambient solar wind near the Sun. The results reveal that both the standard and stealthy CMEs are propelled by the combined action of those forces in the inner corona. The drag force and gravitational force are comparable with the Lorentz force. However, the impact of the drag and Lorentz forces on the global evolution of the stealthy CMEs is significantly weaker than that of the standard CMEs. △ Less

Submitted 23 November, 2022; originally announced November 2022.

Comments: 14 pages, 7 figures, 1 table. Accepted by ApJ

The UV Excesses of Supernovae and the Implications for Studying Supernovae and Other Optical Transients

Authors: Tao Wang, Shan-Qin Wang, Wen-Pei Gan

Abstract: Supernovae (SNe), kilonovae (KNe), tidal disruption events (TDEs), optical afterglows of gamma ray bursts (GRBs), and many other optical transients are important phenomena in time-domain astronomy. Fitting the multi-band light curves (LCs) or the synthesized (pseudo-)bolometric LCs can be used to constrain the physical properties of optical transients. The (UV absorbed) blackbody module is one of… ▽ More Supernovae (SNe), kilonovae (KNe), tidal disruption events (TDEs), optical afterglows of gamma ray bursts (GRBs), and many other optical transients are important phenomena in time-domain astronomy. Fitting the multi-band light curves (LCs) or the synthesized (pseudo-)bolometric LCs can be used to constrain the physical properties of optical transients. The (UV absorbed) blackbody module is one of the most important modules used to fit the multi-band LCs of optical transients having (UV absorbed) blackbody spectral energy distributions (SEDs). We find, however, that the SEDs of some SNe show UV excesses, which cannot be fitted by the model including a (UV absorbed) blackbody module. We construct the bolometric LCs and employ the (cooling plus) \Ni model to fit the constructed bolometric LCs, obtaining decent fits. Our results demonstrate that the optical transients showing UV excesses cannot be fitted by the multi-band models that include (UV-absorbed) blackbody module, but can be well modeled by constructing and fitting their bolometric LCs. △ Less

Submitted 8 October, 2022; originally announced October 2022.

Comments: 9 pages, 4 figures, 1 table, submitted to ApJ

The Study of Dust Formation of Six Tidal Disruption Events

Authors: Xian-Mao Cao, Shan-Qin Wang, Wen-Pei Gan, Jing-Yao Li

Abstract: This paper investigates eleven (UV-)optical-infrared (IR) spectral energy distributions (SEDs) of six tidal disruption events (TDEs), which are ASASSN-14li, ASASSN-15lh, ASASSN-18ul, ASASSN-18zj, PS18kh, and ZTF18acaqdaa. We find that all the SEDs show evident IR excesses. We invoke the blackbody plus dust emission model to fit the SEDs, and find that the model can account for the SEDs. The derive… ▽ More This paper investigates eleven (UV-)optical-infrared (IR) spectral energy distributions (SEDs) of six tidal disruption events (TDEs), which are ASASSN-14li, ASASSN-15lh, ASASSN-18ul, ASASSN-18zj, PS18kh, and ZTF18acaqdaa. We find that all the SEDs show evident IR excesses. We invoke the blackbody plus dust emission model to fit the SEDs, and find that the model can account for the SEDs. The derived masses of the dust surrounding ASASSN-14li, ASASSN-15lh, ASASSN-18ul, ASASSN-18zj, PS18kh, and ZTF18acaqdaa are respectively $\sim0.7-1.0\,(1.5-2.2)\times10^{-4}\,M_\odot$, $\sim0.6-3.1\,(1.4-6.3)\times10^{-2}\,M_\odot$, $\sim1.0\,(2.8)\times10^{-4}\,M_\odot$, $\sim0.1-1.6\,(0.3-3.3)\times10^{-3}\,M_\odot$, $\sim1.0\,(2.0)\times10^{-3}\,M_\odot$, and $\sim 1.1\,(2.9)\times10^{-3}\,M_\odot$, if the dust is graphite (silicate). The temperature of the graphite (silicate) dust of the six TDEs are respectively $\sim1140-1430\,(1210-1520)$\,K, $\sim1030-1380\,(1100-1460)$\,K, $\sim1530\,(1540)$\,K, $\sim960-1380\,(1020-1420)$\,K, $\sim900\,(950)$\,K, and $\sim1600\,(1610)$\,K. By comparing the derived temperatures to the vaporization temperature of graphite ($\sim 1900$\,K) and silicate ($\sim 1100-1500$\,K), we suggest that the IR excesses of PS18kh can be explained by both the graphite and silicate dust, the rest five TDEs favor the graphite dust while the silicate dust model cannot be excluded. Moreover, we demonstrate the lower limits of the radii of the dust shells surrounding the six TDEs are significantly larger than those of the radii of the photospheres at the first epochs of SEDs, indicating that the dust might exist before the the TDEs occurred. △ Less

Submitted 8 October, 2022; originally announced October 2022.

Comments: 13 pages, 4 figures, 4 tables, submitted to ApJ

Plasma heating and nanoflare caused by slow-mode wave in a coronal loop

Authors: Fanxiaoyu Xia, Tongjiang Wang, Yang Su, Jie Zhao, Qingmin Zhang, Astrid M. Veronig, Weiqun Gan

Abstract: We present a detailed analysis of a reflecting intensity perturbation in a large coronal loop that appeared as sloshing oscillation and lasted for at least one and a half periods. The perturbation is initiated by a microflare at one footpoint of the loop, propagates along the loop and is eventually reflected at the remote footpoint where significant brightenings are observed in all the AIA extreme… ▽ More We present a detailed analysis of a reflecting intensity perturbation in a large coronal loop that appeared as sloshing oscillation and lasted for at least one and a half periods. The perturbation is initiated by a microflare at one footpoint of the loop, propagates along the loop and is eventually reflected at the remote footpoint where significant brightenings are observed in all the AIA extreme-ultraviolet (EUV) channels. This unique observation provides us with the opportunity to better understand not only the thermal properties and damping mechanisms of the sloshing oscillation, but also the energy transfer at the remote footpoint. Based on differential emission measures (DEM) analysis and the technique of coronal seismology, we find that 1) the calculated local sound speed is consistent with the observed propagation speed of the perturbation during the oscillation, which is suggestive of a slow magnetoacoustic wave; 2) thermal conduction is the major damping mechanism of the wave but additional damping mechanism such as anomalous enhancement of compressive viscosity or wave leakage is also required to account for the rapid decay of the observed waves; 3) the wave produced a nanoflare at the remote footpoint, with a peak thermal energy of $\thicksim10^{24}-10^{25}$ erg. This work provides a consistent picture of the magnetoacoustic wave propagation and reflection in a coronal loop, and reports the first solid evidence of a wave-induced nanoflare. The results reveal new clues for further simulation studies and may help solving the coronal heating problem. △ Less

Submitted 21 August, 2022; originally announced August 2022.

Comments: 13pages, 5 figures; Accepted by ApJL

The Lyman-$α$ Emission in a C1.4 Solar Flare Observed by the Extreme Ultraviolet Imager aboard Solar Orbiter

Authors: Ying Li, Qiao Li, De-Chao Song, Andrea Francesco Battaglia, Hualin Xiao, Säm Krucker, Udo Schühle, Hui Li, Weiqun Gan, M. D. Ding

Abstract: The hydrogen Lyman-$α$ (H {\sc i} Ly$α$) emission during solar flares has rarely been studied in spatially resolved images and its physical origin has not been fully understood. In this paper, we present novel Ly$α$ images for a C1.4 solar flare (SOL2021-08-20T22:00) from the Extreme Ultraviolet Imager aboard Solar Orbiter, together with multi-waveband and multi-perspective observations from the S… ▽ More The hydrogen Lyman-$α$ (H {\sc i} Ly$α$) emission during solar flares has rarely been studied in spatially resolved images and its physical origin has not been fully understood. In this paper, we present novel Ly$α$ images for a C1.4 solar flare (SOL2021-08-20T22:00) from the Extreme Ultraviolet Imager aboard Solar Orbiter, together with multi-waveband and multi-perspective observations from the Solar Terrestrial Relations Observatory Ahead and the Solar Dynamics Observatory spacecraft. It is found that the Ly$α$ emission has a good temporal correlation with the thermal emissions at 1--8 Å and 5--7 keV, indicating that the flaring Ly$α$ is mainly produced by a thermal process in this small event. However, nonthermal electrons play a minor role in generating Ly$α$ at flare ribbons during the rise phase of the flare, as revealed by the hard X-ray imaging and spectral fitting. Besides originating from flare ribbons, the Ly$α$ emission can come from flare loops, likely caused by plasma heating and also cooling that happen in different flare phases. It is also found that the Ly$α$ emission shows fairly similar features with the He {\sc ii} 304 Å emission in light curve and spatio-temporal variation along with small differences. These observational results improve our understanding of the Ly$α$ emission in solar flares and also provide some insights for investigating the Ly$α$ emission in stellar flares. △ Less

Submitted 12 August, 2022; originally announced August 2022.

Comments: 19 pages, 7 figures, and 2 tables. ApJ accepted. Comments are welcome

Understanding quantum black holes from quantum reduced loop gravity

Authors: Wen-Cong Gan, Geeth Ongole, Emanuele Alesci, Yang An, Fu-Wen Shu, Anzhong Wang

Abstract: We systematically study the top-down model of loop quantum black holes (LQBHs), recently derived by Alesci, Bahrami and Pranzetti (ABP). To understand the structure of the model, we first derive several well-known LQBH solutions by taking proper limits. These include the Böhmer-Vandersloot and Ashtekar-Olmedo-Singh models, which were all obtained by the so-called bottom-up polymerizations within t… ▽ More We systematically study the top-down model of loop quantum black holes (LQBHs), recently derived by Alesci, Bahrami and Pranzetti (ABP). To understand the structure of the model, we first derive several well-known LQBH solutions by taking proper limits. These include the Böhmer-Vandersloot and Ashtekar-Olmedo-Singh models, which were all obtained by the so-called bottom-up polymerizations within the framework of the minisuperspace quantizations. Then, we study the ABP model, and find that the inverse volume corrections become important only when the radius of the two-sphere is of the Planck size. For macroscopic black holes, the minimal radius obtained at the transition surface is always much larger than the Planck scale, and hence these corrections are always sub-leading. The transition surface divides the whole spacetime into two regions, and in one of them the spacetime is asymptotically Schwarzschild-like, while in the other region, the asymptotical behavior sensitively depends on the ratio of two spin numbers involved in the model, and can be divided into three different classes. In one class, the spacetime in the 2-planes orthogonal to the two spheres is asymptotically flat, and in the second one it is not even conformally flat, while in the third one it can be asymptotically conformally flat by properly choosing the free parameters of the model. In the latter, it is asymptotically de Sitter. However, in any of these three classes, sharply in contrast to the models obtained by the bottom-up approach, the spacetime is already geodesically complete, and no additional extensions are needed in both sides of the transition surface. In particular, identical multiple black hole and white hole structures do not exist. △ Less

Submitted 22 December, 2022; v1 submitted 14 June, 2022; originally announced June 2022.

Comments: revtex4-2, 18 figures, and four tables, v3: typos corrected, published in PRD

Journal ref: Phys.Rev.D. 106, 126013 (2022)

Spatially Resolved Moving Radio Burst in Association with an EUV Wave

Authors: Lei Lu, Li Feng, Weiqun Gan

Abstract: Coronal mass ejections (CMEs) are large clouds of magnetized plasma ejected from the Sun, and are often associated with acceleration of electrons that can result in radio emission via various mechanisms. However, the underlying mechanism relating the CMEs and particle acceleration still remains a subject of heated debate. Here, we report multi-instrument radio and extreme ultraviolet (EUV) imaging… ▽ More Coronal mass ejections (CMEs) are large clouds of magnetized plasma ejected from the Sun, and are often associated with acceleration of electrons that can result in radio emission via various mechanisms. However, the underlying mechanism relating the CMEs and particle acceleration still remains a subject of heated debate. Here, we report multi-instrument radio and extreme ultraviolet (EUV) imaging of a solar eruption event on 24 September 2011. We determine the emission mechanism of a moving radio burst, identify its three-dimensional (3D) location with respect to a rapidly expanding EUV wave, and find evidence for CME shocks that produce quasiperiodic acceleration of electron beams. △ Less

Submitted 6 May, 2022; originally announced May 2022.

Comments: 17 pages, 6 figures, accepted by APJL

Report number: AAS38370R2

The Lick Observatory Supernova Search follow-up program: photometry data release of 70 stripped-envelope supernovae

Authors: WeiKang Zheng, Benjamin E. Stahl, Thomas de Jaeger, Alexei V. Filippenko, Shan-Qin Wang, Wen-Pei Gan, Thomas G. Brink, Ivan Altunin, Raphael Baer-Way, Andrew Bigley, Kyle Blanchard, Peter K. Blanchard, James Bradley, Samantha K. Cargill, Chadwick Casper, Teagan Chapman, Vidhi Chander, Sanyum Channa, Byung Yun Choi, Nick Choksi, Matthew Chu, Kelsey I. Clubb, Daniel P. Cohen, Paul A. Dalba, Asia deGraw , et al. (63 additional authors not shown)

Abstract: We present BVRI and unfiltered Clear light curves of 70 stripped-envelope supernovae (SESNe), observed between 2003 and 2020, from the Lick Observatory Supernova Search (LOSS) follow-up program. Our SESN sample consists of 19 spectroscopically normal SNe~Ib, two peculiar SNe Ib, six SN Ibn, 14 normal SNe Ic, one peculiar SN Ic, ten SNe Ic-BL, 15 SNe IIb, one ambiguous SN IIb/Ib/c, and two superlum… ▽ More We present BVRI and unfiltered Clear light curves of 70 stripped-envelope supernovae (SESNe), observed between 2003 and 2020, from the Lick Observatory Supernova Search (LOSS) follow-up program. Our SESN sample consists of 19 spectroscopically normal SNe~Ib, two peculiar SNe Ib, six SN Ibn, 14 normal SNe Ic, one peculiar SN Ic, ten SNe Ic-BL, 15 SNe IIb, one ambiguous SN IIb/Ib/c, and two superluminous SNe. Our follow-up photometry has (on a per-SN basis) a mean coverage of 81 photometric points (median of 58 points) and a mean cadence of 3.6d (median of 1.2d). From our full sample, a subset of 38 SNe have pre-maximum coverage in at least one passband, allowing for the peak brightness of each SN in this subset to be quantitatively determined. We describe our data collection and processing techniques, with emphasis toward our automated photometry pipeline, from which we derive publicly available data products to enable and encourage further study by the community. Using these data products, we derive host-galaxy extinction values through the empirical colour evolution relationship and, for the first time, produce accurate rise-time measurements for a large sample of SESNe in both optical and infrared passbands. By modeling multiband light curves, we find that SNe Ic tend to have lower ejecta masses and lower ejecta velocities than SNe~Ib and IIb, but higher $^{56}$Ni masses. △ Less

Submitted 10 March, 2022; originally announced March 2022.

Comments: Accepted by MNRAS

Three-dimensional analyses of an aspherical coronal mass ejection and its driven shock

Authors: Beili Ying, Li Feng, Bernd Inhester, Marilena Mierla, Weiqun Gan, Lei Lu, Shuting Li

Abstract: Context. Observations reveal that shocks can be driven by fast coronal mass ejections (CMEs) and play essential roles in particle accelerations. A critical ratio, $δ$, derived from a shock standoff distance normalized by the radius of curvature (ROC) of a CME, allows us to estimate shock and ambient coronal parameters. However, true ROCs of CMEs are difficult to measure due to observed projection… ▽ More Context. Observations reveal that shocks can be driven by fast coronal mass ejections (CMEs) and play essential roles in particle accelerations. A critical ratio, $δ$, derived from a shock standoff distance normalized by the radius of curvature (ROC) of a CME, allows us to estimate shock and ambient coronal parameters. However, true ROCs of CMEs are difficult to measure due to observed projection effects. Aims. We investigate the formation mechanism of a shock driven by an aspherical CME without evident lateral expansion. Through three-dimensional (3D) reconstructions without a priori assumptions of the object morphology, we estimate two principal ROCs of the CME surface and demonstrate how the difference between two principal ROCs of the CME affects the estimate of the coronal physical parameters. Methods. The CME was observed by the Sun Earth Connection Coronal and Heliospheric Investigation (SECCHI) instruments and the Large Angle and Spectrometric Coronagraph (LASCO). We used the mask-fitting method to obtain the irregular 3D shape of the CME and reconstructed the shock surface using the bow-shock model. Through smoothings with fifth-order polynomial functions and Monte Carlo simulations, we calculated the ROCs at the CME nose. Results. We find that (1) the maximal ROC is 2-4 times the minimal ROC of the CME. A significant difference between the CME ROCs implies that the assumption of one ROC of an aspherical CME could cause over-/under- estimations of the shock and coronal parameters. (2) The shock nose obeys the bow-shock formation mechanism, considering the constant standoff distance and the similar speed between the shock and CME around the nose. (3) With a more precise $δ$ calculated via 3D ROCs in space, we derive corona parameters at high latitudes of about -50$^{\circ}$, including the Alfv{é}n speed and the coronal magnetic field strength. △ Less

Submitted 20 January, 2022; originally announced January 2022.

Comments: 11 pages, 7 figures, 1 table, accepted by A&A

Journal ref: A&A 660, A23 (2022)

GRB 211227A as a peculiar long gamma-ray burst from compact star merger

Authors: Hou-Jun Lü, Hao-Yu Yuan, Ting-Feng Yi, Xiang-Gao Wang, You-Dong Hu, Yong Yuan, Jared Rice, Jian-Guo Wang, Jia-Xin Cao, De-Feng Kong, Emilio Fernandez-García, Alberto J. Castro-Tirado, Ji-Shun Lian, Wen-Pei Gan, Shan-Qin Wang, Li-Ping Xin, M. D. Caballero-García, Yu-Feng Fan, En-Wei Liang

Abstract: Long-duration gamma-ray bursts (GRBs) associated with supernovae (SNe) are believed to originate from massive star core-collapse events, whereas short-duration GRBs that are related to compact star mergers are expected to be accompanied by kilonovae. GRB 211227A, which lasted about 84 s, had an initial short/hard spike followed by a series of soft gamma-ray extended emission at redshift $z=$0.228.… ▽ More Long-duration gamma-ray bursts (GRBs) associated with supernovae (SNe) are believed to originate from massive star core-collapse events, whereas short-duration GRBs that are related to compact star mergers are expected to be accompanied by kilonovae. GRB 211227A, which lasted about 84 s, had an initial short/hard spike followed by a series of soft gamma-ray extended emission at redshift $z=$0.228. We performed follow-up observations of the optical emission using BOOTES, LCOGT, and the Lijiang 2.4m telescope, but we detected no associated supernova signature, even down to very stringent limits at such a low redshift. We observed the host galaxy within a large error-circle and roughly estimate the physical offset of GRB 211227A as $20.47\pm14.47$ kpc from the galaxy center. These properties are similar to those of GRB 060614, and suggest that the progenitor of GRB 211227A is not favored to be associated with the death of massive stars. Hence, we propose that GRB 211227A originates from a compact star merger. Calculating pseudo-kilonova emission for this case by adopting the typical parameters, we find that any associated pseudo-kilonova is too faint to be detected. If this is the case, it explains naturally the characteristics of the prompt emission, the lack of SN and kilonova emission, and the large physical offset from the galaxy center. △ Less

Submitted 30 May, 2022; v1 submitted 17 January, 2022; originally announced January 2022.

Comments: 12 pages, 7 figures, and 1 Table. Matched with the published verison

Journal ref: ApJL, 931:L23, 2022

Modeling the Multi-band Light Curves of the Afterglows of Three Gamma-Ray Bursts and Their Associated Supernovae

Authors: Ji-Shun Lian, Shan-Qin Wang, Wen-Pei Gan, Jing-Yao Li, En-Wei Liang

Abstract: There are some dozen supernovae (SNe) associated with long Gamma-ray bursts (GRBs) have been confirmed. Most of previous studies derive the physical properties of the GRB-SNe by fitting the constructed (psuedo-)bolometric light curves. However, many GRB-SNe have only a few filter data, for which the (psuedo-)bolometric light curves are very difficult to be constructed. Additionally, constructing (… ▽ More There are some dozen supernovae (SNe) associated with long Gamma-ray bursts (GRBs) have been confirmed. Most of previous studies derive the physical properties of the GRB-SNe by fitting the constructed (psuedo-)bolometric light curves. However, many GRB-SNe have only a few filter data, for which the (psuedo-)bolometric light curves are very difficult to be constructed. Additionally, constructing (psuedo-)bolometric light curves rely on some assumptions. In this paper, we use the multi-band broken power-law plus $^{56}$Ni model to fit the multi-band light curves of the afterglows and the SNe (SN~2001ke, SN~2013dx, and SN~2016jca) associated with three GRBs (GRB~011121, GRB~130702A, and GRB~161219B). We find our model can account for the multi-band light curves of the three GRB-SNe (except for the late-time $z-$band light curves of two events), indicating that the model is a reliable model. The $^{56}$Ni masses we derive are higher than that in the literature. This might be due to the fact that the $^{56}$Ni masses in the literature are usually obtained by fitting the psuedo-bolometric light curves whose luminosities are usually (significantly) underestimated. We suggest that the multi-band model can not only be used to fit the multi-band light curves of GRB-SNe that have many filter observations, but also fit those having sparse data. △ Less

Submitted 21 April, 2022; v1 submitted 21 December, 2021; originally announced December 2021.

Comments: 17 pages, 6 figures, 4 tables, Accepted for publication in ApJ

iPTF 16asu Revisited: A Rapidly Evolving Superluminous Broad-Lined Ic Supernova?

Authors: Shan-Qin Wang, Wen-Pei Gan

Abstract: In this paper, we fit the spectral energy distributions (SEDs) of iPTF 16asu that has so far been classified as a luminous rapidly evolving broad-lined Ic supernova (SN Ic-BL), and re-construct its post-peak bolometric light curve. We find that the luminosity of the post-peak bolometric light curve of iPTF 16asu is about 3 times that of the pseudo-bolometric light curve derived in the literature,… ▽ More In this paper, we fit the spectral energy distributions (SEDs) of iPTF 16asu that has so far been classified as a luminous rapidly evolving broad-lined Ic supernova (SN Ic-BL), and re-construct its post-peak bolometric light curve. We find that the luminosity of the post-peak bolometric light curve of iPTF 16asu is about 3 times that of the pseudo-bolometric light curve derived in the literature, and the extrapolated peak luminosity exceeds $\sim 10^{44}$ erg s$^{-1}$, which is higher than the threshold of superluminous SNe (SLSNe). We then use the $^{56}$Ni model and the magnetar plus $^{56}$Ni model to fit the multi-band light curves of iPTF 16asu, and construct the theoretical bolometric light curve using the best-fitting theoretical multi-band light curves. We find that the magnetar plus $^{56}$Ni model can account for the photometry of iPTF~16asu, and the peak luminosity of its theoretical bolometric light curve is $\sim 1.06\times 10^{44}$ erg s$^{-1}$. We suggest that iPTF~16asu and similar SNe (e.g., SN 2018gep) constitute the class of rapidly evolving SLSNe Ic-BL. △ Less

Submitted 8 February, 2022; v1 submitted 21 December, 2021; originally announced December 2021.

Comments: 13 pages, 6 figures, 2 tables, Accepted for publication in ApJ

Observational Signatures of Tearing Instability in the Current Sheet of a Solar Flare

Authors: Lei Lu, Li Feng, Alexander Warmuth, Astrid M. Veronig, Jing Huang, Siming Liu, Weiqun Gan, Zongjun Ning, Beili Ying, Guannan Gao

Abstract: Magnetic reconnection is a fundamental physical process converting magnetic energy into not only plasma energy but also particle energy in various astrophysical phenomena. In this letter, we show a unique dataset of a solar flare where various plasmoids were formed by a continually stretched current sheet. EUV images captured reconnection inflows, outflows, and particularly the recurring plasma bl… ▽ More Magnetic reconnection is a fundamental physical process converting magnetic energy into not only plasma energy but also particle energy in various astrophysical phenomena. In this letter, we show a unique dataset of a solar flare where various plasmoids were formed by a continually stretched current sheet. EUV images captured reconnection inflows, outflows, and particularly the recurring plasma blobs (plasmoids). X-ray images reveal nonthermal emission sources at the lower end of the current sheet, presumably as large plasmoids with a sufficiently amount of energetic electrons trapped in. In the radio domain, an upward slowly drifting pulsation structure, followed by a rare pair of oppositely drifting structures, was observed. These structures are supposed to map the evolution of the primary and the secondary plasmoids formed in the current sheet. Our results on plasmoids at different locations and scales shed important light on the dynamics, plasma heating, particle acceleration, and transport processes in the turbulent current sheet and provide observational evidence for the cascading magnetic reconnection process. △ Less

Submitted 3 January, 2022; v1 submitted 14 December, 2021; originally announced December 2021.

Comments: 12 pages, 4 figures, 2 appendix

Report number: AAS36121R1

Using the Optical--NIR Spectral Energy Distributions To Search for the Evidence of Dust Formation of 66 Supernovae

Authors: Jing-Yao Li, Shan-Qin Wang, Wen-Pei Gan, Tao Wang, Ji-Shun Lian, Song-Yao Bai, En-Wei Liang

Abstract: In this paper, we searched for the dust formation evidence of 66 supernovae (SNe) by using the blackbody model and the blackbody plus dust {emission} model to fit their early$-$time optical$-$near infrared (NIR) spectral energy distributions (SEDs). We find that, while the blackbody model can fit most SEDs of the SNe in our sample, the model cannot fit the SEDs of some SNe, in which the SEDs of 2… ▽ More In this paper, we searched for the dust formation evidence of 66 supernovae (SNe) by using the blackbody model and the blackbody plus dust {emission} model to fit their early$-$time optical$-$near infrared (NIR) spectral energy distributions (SEDs). We find that, while the blackbody model can fit most SEDs of the SNe in our sample, the model cannot fit the SEDs of some SNe, in which the SEDs of 2 SNe (SNe~2010bq and 2012ca) show NIR excesses which can be attributed to the emission from the heated dust. We use blackbody plus dust emission model to fit the SEDs showing NIR excesses, finding that both graphite and silicate dust models can fit the SEDs, and the graphite model get reasonable temperatures or better fits. Assuming that the dust is graphite, the best-fitting temperatures (masses) of the dust of the SNe~2010bq and 2012ca are $\sim 1300-1800$ K ($\sim 0.1-3.4 \times 10^{-4}$ M$_\odot$) and $\sim 600-1000$ K ($\sim 0.6-7.5 \times 10^{-3}$ M$_\odot$), respectively. We compare the vaporization radii and the blackbody radii of the dust shells of the 2 SNe with the upper limits of the ejecta radii of the SNe at the first epochs, and demonstrate that the NIR excesses of the SEDs of the 2 SNe might be caused by the pre-existing dust. △ Less

Submitted 13 February, 2022; v1 submitted 28 October, 2021; originally announced October 2021.

Comments: Accepted for publication in ApJ, 48 pages, 12 figures, 5 tables

The Study of Dust Formation of Four Type Ibn Supernovae

Authors: Wen-Pei Gan, Shan-Qin Wang, En-Wei Liang

Abstract: In this paper, we investigate the early-time optical$-$near-infrared (NIR) spectral energy distributions (SEDs) of four Type Ibn supernovae (SNe). We find that the SEDs of SN~2010al, LSQ13ddu, and SN~2015G can be well explained by the single-component blackbody model, while the SEDs of OGLE-2012-SN-006 cannot. We invoke the double-component model assuming that the SEDs were produced by the SN phot… ▽ More In this paper, we investigate the early-time optical$-$near-infrared (NIR) spectral energy distributions (SEDs) of four Type Ibn supernovae (SNe). We find that the SEDs of SN~2010al, LSQ13ddu, and SN~2015G can be well explained by the single-component blackbody model, while the SEDs of OGLE-2012-SN-006 cannot. We invoke the double-component model assuming that the SEDs were produced by the SN photosphere and the heated dust to fit the optical$-$NIR SEDs of the four SNe Ibn, finding that the derived temperatures of the dust associated with OGLE-2012-SN-006 favor the scenario that the dust consists of the graphite grains, and the mass and temperature of dust are $\sim$$0.5-2.0\times10^{-3}~M_\odot$ and $\sim$ $1200-1300$ K, respectively. Moreover, our fits for SN~2010al, LSQ13ddu, and SN~2015G show that the upper limits of the masses of the dust associated with the three SNe Ibn are respectively $1.45\times 10^{-5}~M_\odot$, $5.9\times 10^{-7}~M_\odot$, and $2.4\times 10^{-7}~M_\odot$. A further analysis demonstrates that the inferred radius of the dust shell surrounding OGLE-2012-SN-006 is significantly larger than that of the SN ejecta at early epochs, indicating that the NIR excesses of the SEDs of OGLE-2012-SN-006 were produced by a preexisting dust shell. Our study for the early-time SEDs of four SNe Ibn, together with the previous studies and the fact that some SNe showed the evidence of dust formation at the late-time SEDs, indicates that at least $\sim$1/3 of SNe Ibn show evidence for dust formation. △ Less

Submitted 24 September, 2021; originally announced September 2021.

Comments: published in ApJ on June 23, 2021; 21 pages, 9 figures, 3 tables

Journal ref: The Astrophysical Journal, 914, 125(16pp), 2021 June 20

Multi-wavelength and Dual-perspective Observations of Eruption and Untwisting of Two Homologous Magnetic Flux Ropes

Authors: De-Chao Song, Y. Li, Y. Su, M. D. Ding, W. Q. Gan

Abstract: In this paper, we present a detailed morphological, kinematic, and thermal analysis of two homologous magnetic flux ropes (MFRs) from NOAA 11515 on 2012 July 8--9. The study is based on multi-wavelength and dual-perspective imaging observations from the Solar Dynamics Observatory and the Solar Terrestrial Relations Observatory Ahead spacecraft, which can well reveal the structure and evolution of… ▽ More In this paper, we present a detailed morphological, kinematic, and thermal analysis of two homologous magnetic flux ropes (MFRs) from NOAA 11515 on 2012 July 8--9. The study is based on multi-wavelength and dual-perspective imaging observations from the Solar Dynamics Observatory and the Solar Terrestrial Relations Observatory Ahead spacecraft, which can well reveal the structure and evolution of the two MFRs. We find that both of the MFRs show up in multiple passbands and their emissions mainly consist of a cold component peaking at a temperature of $\sim$0.4--0.6 MK and a hot component peaking at $\sim$7--8 MK. The two MFRs exhibit erupting, expanding, and untwisting motions that manifest distinctive features from two different viewpoints. Their evolution can be divided into two stages, a fast-eruption stage with speeds of about 105--125 km s$^{-1}$ for MFR-1 and 50--65 km s$^{-1}$ for MFR-2 and a slow-expansion (or untwisting) stage with speeds of about 10--35 km s$^{-1}$ for MFR-1 and 10--30 km s$^{-1}$ for MFR-2 in the plane of sky. We also find that during the two-stage evolution, the high temperature features mainly appear in the interface region between MFRs and ambient magnetic structures and also in the center of MFRs, which suggests that some heating processes take place in such places like magnetic reconnection and plasma compression. These observational results indicate that the eruption and untwisting processes of MFRs are coupled with the heating process, among which an energy conversion exists. △ Less

Submitted 23 September, 2021; originally announced September 2021.

Comments: 24 pages, 10 figures, 1 table

Quasi-Periodic Pulsations Detected in Ly$α$ and Nonthermal Emissions During Solar Flares

Authors: Lei Lu, Dong Li, Zongjun Ning, Li Feng, Weiqun Gan

Abstract: We report quasi-periodic pulsations (QPPs) with double periods during three solar flares (viz. SOL2011-Feb-15T01:44, SOL2011-Sep-25T04:31, SOL2012-May-17T01:25). The flare QPPs were observed from light curves in Ly$α$, hard X-ray (HXR) and microwave emissions, with the Ly$α$ emission recorded by the Geostationary Operational Environmental Satellite, the HXR emission recorded by the Reuven Ramaty H… ▽ More We report quasi-periodic pulsations (QPPs) with double periods during three solar flares (viz. SOL2011-Feb-15T01:44, SOL2011-Sep-25T04:31, SOL2012-May-17T01:25). The flare QPPs were observed from light curves in Ly$α$, hard X-ray (HXR) and microwave emissions, with the Ly$α$ emission recorded by the Geostationary Operational Environmental Satellite, the HXR emission recorded by the Reuven Ramaty High-Energy Solar Spectroscopic Imager and the Fermi Gamma-ray Burst Monitor, and the microwave emission recorded by the Nobeyama Radio Polarimeters and Radioheliograph. By using the Markov chain Monte Carlo (MCMC) method, QPPs with double periods of about two minutes and one minute were first found in the Ly$α$ emission. Then using the same method, a QPP with nearly the same period of about two minutes was also found in HXR and microwave emissions. Considering the possible common origin (nonthermal electrons) between Ly$α$ and HXR/microwave emission, we suggest that the two-minute QPP results from the periodic acceleration of nonthermal electrons during magnetic reconnections. The ratio between the double periods in the Ly$α$ emission was found to be close to two, which is consistent with the theoretical expectation between the fundamental and harmonic modes. However, we cannot rule out other possible driving mechanisms for the one-minute QPPs in HXR/microwave emissions due to their relatively large deviations. △ Less

Submitted 9 August, 2021; originally announced August 2021.

Comments: 24 pages, 9 figures, 2 tables

Detection of flare multi-periodic pulsations in mid-ultraviolet Balmer continuum, Ly-alpha, hard X-ray, and radio emissions simultaneously

Authors: Dong Li, Mingyu Ge, Marie Dominique, Haisheng Zhao, Gang Li, Xiaobo Li, Shuangnan Zhang, Fangjun Lu, Weiqun Gan, Zongjun Ning

Abstract: Quasi-periodic pulsations (QPPs), which usually appear as temporal pulsations of the total flux, are frequently detected in the light curves of solar/stellar flares. In this study, we present the investigation of non-stationary QPPs with multiple periods during the impulsive phase of a powerful flare on 2017 September 06, which were simultane- ously measured by the Large-Yield RAdiometer (LYRA) an… ▽ More Quasi-periodic pulsations (QPPs), which usually appear as temporal pulsations of the total flux, are frequently detected in the light curves of solar/stellar flares. In this study, we present the investigation of non-stationary QPPs with multiple periods during the impulsive phase of a powerful flare on 2017 September 06, which were simultane- ously measured by the Large-Yield RAdiometer (LYRA) and the Hard X-ray Modula- tion Telescope (Insight-HXMT), as well as the ground-based BLENSW. The multiple periods, detected by applying a wavelet transform and Lomb-Scargle periodogram to the detrended light curves, are found to be about 20-55 s in the Ly-alpha and mid-ultraviolet Balmer continuum emissions during the flare impulsive phase. Similar QPPs with multi- ple periods are also found in the hard X-ray emission and low-frequency radio emission. Our observations suggest that the flare QPPs could be related to nonthermal electrons accelerated by the repeated energy release process, i.e., triggering of repetitive magnetic reconnection, while the multiple periods might be modulated by the sausage oscillation of hot plasma loops. For the multi-periodic pulsations, other generation mechanisms could not be completely ruled out. △ Less

Submitted 8 August, 2021; originally announced August 2021.

Comments: Accepted for publication in The Astrophysical Journal

Analysis of type II and type III radio bursts associated with SEPs from non-interacting/interacting radio-loud CMEs

Authors: P Pappa Kalaivani, O Prakash, A Shanmugaraju, Li Feng, Lei Lu, Weiqun Gan, G Michalek

Abstract: We analyze radio bursts observed in events with interacting/non-interacting CMEs that produced major SEPs (Ip $>$ 10 MeV) fromApril 1997 to December 2014.We compare properties of meter (m), deca-hectometer (DH) type II as well as DH type III bursts, and time lags for interacting-CME-associated (IC) events and non-interacting-CME-associated (NIC) events. About 70\% of radio emissions were observed… ▽ More We analyze radio bursts observed in events with interacting/non-interacting CMEs that produced major SEPs (Ip $>$ 10 MeV) fromApril 1997 to December 2014.We compare properties of meter (m), deca-hectometer (DH) type II as well as DH type III bursts, and time lags for interacting-CME-associated (IC) events and non-interacting-CME-associated (NIC) events. About 70\% of radio emissions were observed in events of both types from meters to kilometers. We found high correlations between the drift rates and mid-frequencies of type II radio bursts calculated as the mean geometric between their starting and ending frequencies for both NIC and IC-associated events (Correlation coefficient \textit{R}$^{2}$ = 0.98, power-law index $\varepsilon$ = 1.68 $\pm $ 0.16 and \textit{R}$^{2}$ = 0.93, $\varepsilon$ = 1.64 $\pm $ 0.19 respectively).We also found a correlation between the frequency drift rates of DH type II bursts and space speeds of CMEs in NIC-associated events. The absence of such correlation for IC-associated events confirms that the shock speeds changed in CME--CME interactions. For the events with western source locations, the mean peak intensity of SEPs in IC-associated events is four times larger than that in NIC-associated SEP events. From the mean time lags between the start times of SEP events and the start of m, DH type II, and DH type III radio bursts, we inferred that particle enhancements in NIC-associated SEP events occurred earlier than in IC-associated SEP events. The difference between NIC events and IC events in the mean values of parameters of type II and type III bursts is statistically insignificant. △ Less

Submitted 21 July, 2021; originally announced July 2021.

Comments: 15 pages, 4 figures, 2 tables

MSC Class: 14J60 ACM Class: F.2.2

Journal ref: Astrophysics, 2021

Three-Dimensional Reconstructions of Coronal Wave Surfaces Using a New Mask-Fitting Method

Authors: Li Feng, Lei Lu, Bernd Inhester, Joseph Plowman, Beili Ying, Marilena Mierla, Matthew J. West, Weiqun Gan

Abstract: Coronal waves are large-scale disturbances often driven by coronal mass ejections (CMEs). We investigate a spectacular wave event on 7 March 2012, which is associated with an X5.4 flare (SOL2012-03-07). By using a running center-median (RCM) filtering method for the detection of temporal variations in extreme ultraviolet (EUV) images, we enhance the EUV disturbance observed by the Atmospheric Imag… ▽ More Coronal waves are large-scale disturbances often driven by coronal mass ejections (CMEs). We investigate a spectacular wave event on 7 March 2012, which is associated with an X5.4 flare (SOL2012-03-07). By using a running center-median (RCM) filtering method for the detection of temporal variations in extreme ultraviolet (EUV) images, we enhance the EUV disturbance observed by the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) and the Sun Watcher using Active Pixel System detector and Image Processing (SWAP) onboard the PRoject for Onboard Autonomy 2 (PROBA2). In coronagraph images, a halo front is observed to be the upper counterpart of the EUV disturbance. Based on the EUV and coronagraph images observed from three different perspectives, we have made three-dimensional (3D) reconstructions of the wave surfaces using a new mask-fitting method. The reconstructions are compared with those obtained from forward-fitting methods. We show that the mask fitting method can reflect the inhomogeneous coronal medium by capturing the concave shape of the shock wave front. Subsequently, we trace the developing concave structure and derive the deprojected wave kinematics. The speed of the 3D-wave nose increases from a low value below a few hundred $\mathrm{km\,s^{-1}}$ to a maximum value of about 3800 $\mathrm{km\,s^{-1}}$, and then slowly decreases afterwards. The concave structure starts to decelerate earlier and has significantly lower speeds than those of the wave nose. We also find that the 3D-wave in the extended corona has a much higher speed than the speed of EUV disturbances across the solar disk. △ Less

Submitted 22 September, 2020; originally announced September 2020.

Comments: Solar Physics: Topical Collection "Ten Years of Solar Observations with PROBA2", accepted

Properties of the spherically symmetric polymer black holes

Authors: Wen-Cong Gan, Nilton O. Santos, Fu-Wen Shu, Anzhong Wang

Abstract: In this paper we systematically study a five-parameters class of spherically symmetric polymer black/white hole solutions, and find that only three independent combinations are physical and uniquely determine the spacetime properties. After exploring the whole 3-dimensional (3D) phase space, we find that the model has very rich physics, and depending on the choice of these parameters, various poss… ▽ More In this paper we systematically study a five-parameters class of spherically symmetric polymer black/white hole solutions, and find that only three independent combinations are physical and uniquely determine the spacetime properties. After exploring the whole 3-dimensional (3D) phase space, we find that the model has very rich physics, and depending on the choice of these parameters, various possibilities exist, including: (i) spacetimes that have the standard black/white hole structures, that is, spacetimes that are free of spacetime curvature singularities and possess two asymptotically flat regions, which are connected by a transition surface (throat) with a finite and non-zero geometric radius. The black/white hole masses measured by observers in the two asymptotically flat regions are all positive, and the surface gravity of the black (white) hole is positive (negative). (ii) Spacetimes that have wormhole-like structures, in which the two masses are all positive, but no horizons exist.(iii) Spacetimes that still possess curvature singularities, which can be either hidden inside trapped regions or naked. However, such spacetimes correspond to only some limit cases, and the necessary (but not sufficient) condition is that at least one of the two "polymerization" parameters vanishes. In addition, even for solar mass black/white holes, quantum gravitational effects can be still very large at the black/white hole horizons, again depending on the choice of the parameters. △ Less

Submitted 15 March, 2022; v1 submitted 21 August, 2020; originally announced August 2020.

Comments: 37 pages, 18 figures, 4 tables, v2: title changed, typos corrected, paragraphs and references added, published version

Journal ref: Phys. Rev. D 102, 124030 (2020)

Extensive Study of a Coronal Mass Ejection with UV and WL coronagraphs: the need for multi-wavelength observations

Authors: Beili Ying, Alessandro Bemporad, Li Feng, Lei Lu, Weiqun Gan, Hui Li

Abstract: Coronal Mass Ejections (CMEs) often show different features in different band-passes. By combining data in white-light (WL) and ultraviolet (UV) bands, we have applied different techniques to derive plasma temperatures, electron density, internal radial speed, etc, within a fast CME. They serve as extensive tests of the diagnostic capabilities, developed for the observations provided by future mul… ▽ More Coronal Mass Ejections (CMEs) often show different features in different band-passes. By combining data in white-light (WL) and ultraviolet (UV) bands, we have applied different techniques to derive plasma temperatures, electron density, internal radial speed, etc, within a fast CME. They serve as extensive tests of the diagnostic capabilities, developed for the observations provided by future multi-channel coronagraphs (such as Solar Orbiter/Metis, ASO-S/LST, PROBA-3/ASPIICS). The involved data include WL images acquired by SOHO/LASCO coronagraphs, and intensities measured by SOHO/UVCS at 2.45 R$_{\odot}$ in the UV (H I Ly$α$ and O VI 1032 {AA} lines) and WL channels. Data from the UVCS WL channel have been employed for the first time to measure the CME position angle with polarization-ratio technique. Plasma electron and effective temperatures of the CME core and void are estimated by combining UV and WL data. Due to the CME expansion and the possible existence of prominence segments, the transit of the CME core results in decreases of the electron temperature down to $10^{5}$ K. The front is observed as a significant dimming in the Ly$α$ intensity, associated with a line broadening due to plasma heating and flows along the line-of-sight. The 2D distribution of plasma speeds within the CME body is reconstructed from LASCO images and employed to constrain the Doppler dimming of Ly$α$ line, and simulate future CME observations by Metis and LST. △ Less

Submitted 9 July, 2020; originally announced July 2020.

Comments: Accepted by ApJ, 22 pages, 12 figures

Quasi-periodic pulsation detected in Lyman-alpha emission during solar flares

Authors: Dong Li, Lei Lu, Zongjun Ning, Li Feng, Weiqun Gan, Hui Li

Abstract: We investigated the quasi-periodic pulsation (QPP) in Lyman-alpha, X-ray and extreme-ultraviolet (EUV) emissions during two solar flares, i.e., an X-class (SOL2012-01-27T) and a C-class (SOL2016-02-08T). The full-disk Lyman-alpha and X-Ray flux during these solar flares were recorded by the EUV Sensor and X-Ray Sensor on board the Geostationary Operational Environmental Satellite. The °are regions… ▽ More We investigated the quasi-periodic pulsation (QPP) in Lyman-alpha, X-ray and extreme-ultraviolet (EUV) emissions during two solar flares, i.e., an X-class (SOL2012-01-27T) and a C-class (SOL2016-02-08T). The full-disk Lyman-alpha and X-Ray flux during these solar flares were recorded by the EUV Sensor and X-Ray Sensor on board the Geostationary Operational Environmental Satellite. The °are regions were located from the EUV images measured by the Atmospheric Imaging Assembly. The QPP could be identified as a series of regular and periodic peaks in the light curves, and its quasi-periodicity was determined from the global wavelet and Fourier power spectra. A quasi-periodicity at about 3 minutes is detected during the impulsive phase of the X-class flare, which could be explained as the acoustic wave in the chromosphere (e.g., Milligan et al. 2017). Interestingly, a quasi-periodicity at roughly 1 minute is discovered during the entire evolutionary phases of solar flares, including the precursor, impulsive, and gradual phases. This is the first report of 1-minute QPP in the Lyman-alpha emission during solar flares, in particular during the flare precursor. It may be interpreted as a self-oscillatory regime of the magnetic reconnection, such as magnetic dripping. △ Less

Submitted 3 March, 2020; originally announced March 2020.

Comments: 21 pages, 7 figures, accepted for publication in The Astrophysical Journal

Relationships between Photospheric Vertical Electric Currents and Hard X-Ray Sources in Solar Flares: Statistical Study

Authors: I. V. Zimovets, I. N. Sharykin, W. Q. Gan

Abstract: There are still debates whether particle acceleration in solar flares may occur due to interruption of electric currents flowing along magnetic loops. To contribute to this problem, we performed the first statistical study of relationships between flare hard X-ray (HXR; $50-100$ keV) sources observed by the \textit{Ramaty High-Energy Solar Spectroscopic Imager} (RHESSI) and photospheric vertical e… ▽ More There are still debates whether particle acceleration in solar flares may occur due to interruption of electric currents flowing along magnetic loops. To contribute to this problem, we performed the first statistical study of relationships between flare hard X-ray (HXR; $50-100$ keV) sources observed by the \textit{Ramaty High-Energy Solar Spectroscopic Imager} (RHESSI) and photospheric vertical electric currents (PVECs, $j_{r}$) calculated using vector magnetograms obtained with the Helioseismic and Magnetic Imager (HMI) on-board the \textit{Solar Dynamics Observatory} (SDO). A sample of 48 flares, from C3.0 to X3.1 class, observed in central part of the solar disk by both instruments in 2010--2015 was analyzed. We found that $\approx 70$\% of all HXR sources overlapped with islands or ribbons of enhanced ($\left| j_{r} \right| \gtrsim 10^{4}$ statampere~cm$^{-2}$) PVECs. However, less than $\approx 40$\% of the HXR sources overlapped with PVEC maxima, with an accuracy of $\pm 3^{\prime\prime}$. More than in half of the flares there were HXR sources outside regions of enhanced PVECs. We found no correlation between intensity of the HXR sources and PVEC density or total PVEC under them. No systematic dissipation of PVECs under the HXR sources was found during the flares. Collectively, the results do not support the current-interruption flare models. However, the results indicate the importance of the presence of longitudinal currents in flare regions. Understanding of their specific role in the processes of energy release, plasma heating, and acceleration of particles requires further investigation. △ Less

Submitted 16 February, 2020; originally announced February 2020.

Comments: 56 pages, 21 figures, accepted in ApJ