Showing 1–50 of 357 results for author: Xu, Z

The Simons Observatory: forecasted constraints on primordial gravitational waves with the expanded array of Small Aperture Telescopes

Authors: The Simons Observatory Collaboration, I. Abril-Cabezas, S. Adachi, P. Ade, A. E. Adler, P. Agrawal, J. Aguirre, S. Aiola, T. Alford, A. Ali, D. Alonso, M. A. Alvarez, R. An, M. Aravena, K. Arnold, P. Ashton, F. Astori, Z. Atkins, J. Austermann, S. Azzoni, C. Baccigalupi, D. Baker, R. Balafendiev, A. Baleato Lizancos, D. Barron , et al. (457 additional authors not shown)

Abstract: We present updated forecasts for the scientific performance of the degree-scale (0.5 deg FWHM at 93 GHz), deep-field survey to be conducted by the Simons Observatory (SO). By 2027, the SO Small Aperture Telescope (SAT) complement will be doubled from three to six telescopes, including a doubling of the detector count in the 93 GHz and 145 GHz channels to 48,160 detectors. Combined with a planned e… ▽ More We present updated forecasts for the scientific performance of the degree-scale (0.5 deg FWHM at 93 GHz), deep-field survey to be conducted by the Simons Observatory (SO). By 2027, the SO Small Aperture Telescope (SAT) complement will be doubled from three to six telescopes, including a doubling of the detector count in the 93 GHz and 145 GHz channels to 48,160 detectors. Combined with a planned extension of the survey duration to 2035, this expansion will significantly enhance SO's search for a $B$-mode signal in the polarisation of the cosmic microwave background, a potential signature of gravitational waves produced in the very early Universe. Assuming a $1/f$ noise model with knee multipole $\ell_{\rm knee} = 50$ and a moderately complex model for Galactic foregrounds, we forecast a $1σ$ (or 68% confidence level) constraint on the tensor-to-scalar ratio $r$ of $σ_r = 1.2\times10^{-3}$, assuming no primordial $B$-modes are present. This forecast assumes that 70% of the $B$-mode lensing signal can ultimately be removed using high resolution observations from the SO Large Aperture Telescope (LAT) and overlapping large-scale structure surveys. For more optimistic assumptions regarding foregrounds and noise, and assuming the same level of delensing, this forecast constraint improves to $σ_r = 7\times10^{-4}$. These forecasts represent a major improvement in SO's constraining power, being a factor of around 2.5 times better than what could be achieved with the originally planned campaign, which assumed the existing three SATs would conduct a five-year survey. △ Less

Submitted 17 December, 2025; originally announced December 2025.

Comments: 15 pages (excluding front matter), 4 figures, for submission to JCAP

Measurement of the cosmic ray nickel energy spectrum from 10 GeV/n to 2 TeV/n with the DAMPE

Authors: F. Alemanno, Q. An, P. Azzarello, F. C. T. Barbato, P. Bernardini, X. J. Bi, H. V. Boutin, I. Cagnoli, M. S. Cai, E. Casilli, J. Chang, D. Y. Chen, J. L. Chen, Z. F. Chen, Z. X. Chen, P. Coppin, M. Y. Cui, T. S. Cui, I. De Mitri, F. de Palma, A. Di Giovanni, T. K. Dong, Z. X. Dong, G. Donvito, J. L. Duan , et al. (123 additional authors not shown)

Abstract: Nickel, one of the most stable elements alongside iron, is the most abundant heavy element beyond iron in cosmic rays. With DAMPE's excellent charge resolution and broad energy range, a high-precision energy spectrum provides valuable insights into the acceleration sources of heavy nuclei and their propagation through the interstellar medium. In this analysis, we report the direct measurement of c… ▽ More Nickel, one of the most stable elements alongside iron, is the most abundant heavy element beyond iron in cosmic rays. With DAMPE's excellent charge resolution and broad energy range, a high-precision energy spectrum provides valuable insights into the acceleration sources of heavy nuclei and their propagation through the interstellar medium. In this analysis, we report the direct measurement of cosmic-ray nickel spectrum from 10 GeV/n to 2 TeV/n with nine years of flight data. The nickel spectrum is consistent with a single power law with spectral index -2.60 +/- 0.03 from 40 GeV/n to 1 TeV/n. This work provides an accurate measurement of differential flux of nickel with kinetic energy extending to TeV/n for the first time. △ Less

Submitted 12 December, 2025; originally announced December 2025.

Deep Neural Network-Based High-Precision Identification of Weak Stability Boundary Structures

Authors: Shuyue Fu, Ziqi Xu, Di Wu, Shengping Gong

Abstract: Weak stability boundary structures have been widely applied to the analysis on ballistic capture and the construction of low-energy transfers. The first step of this application is to compute/identify weak stability boundary structures. Conventional numerical and analytical methods cannot simultaneously achieve computational efficiency and identification precision. In this paper, we propose an eff… ▽ More Weak stability boundary structures have been widely applied to the analysis on ballistic capture and the construction of low-energy transfers. The first step of this application is to compute/identify weak stability boundary structures. Conventional numerical and analytical methods cannot simultaneously achieve computational efficiency and identification precision. In this paper, we propose an efficient and precise method to identify weak stability boundary structures based on deep neural network. The geometric and dynamical properties of weak stability boundary structures are firstly analyzed, which provides further insights into the training of the deep neural network models. Then, the optimal hyperparameter combinations are determined by examining the identification precision of the trained deep neural network models. The performance of the models with the optimal hyperparameter combinations is further validated using the representative test datasets, achieving the precision of 97.26-99.91%. The trained models are also applied to constructing weak stability boundary structures. △ Less

Submitted 29 November, 2025; originally announced December 2025.

Multiwavelength Observations for a Double-decker Filament Channel in AR 13102

Authors: Yin Zhang, Baolin Tan, Quan Wang, Jing Huang, Zhe Xu, Kanfan Ji, Xiao Yang, Jie Chen, Xianyong Bai, Zhenyong Hou, Yuanyong Deng

Abstract: We present the observational evidence of the existence of a double-decker filament channel (FC) by using observations in extreme ultraviolet and Hα wavelengths. For both FCs, the east foot-point roots in the active region (AR), while the west one roots in the remote quiet region. The bottom FC (FC1) appears as intermittent filaments. Within the AR, the FC1 appears as an S-shaped filament (F1), whi… ▽ More We present the observational evidence of the existence of a double-decker filament channel (FC) by using observations in extreme ultraviolet and Hα wavelengths. For both FCs, the east foot-point roots in the active region (AR), while the west one roots in the remote quiet region. The bottom FC (FC1) appears as intermittent filaments. Within the AR, the FC1 appears as an S-shaped filament (F1), which consisted of two J-shaped filaments (F1S/F1N for the south/north one). For the upper one (FC2), only the east part is filled with dark plasma and visible as a small filament (F2). Its east foot-point roots around the junction of F1S and F1N. Initially, due to the recurrent reconnections, F1N and F1S link to each other and form a new filament (F3) thread by thread. Meanwhile, the heated plasma, which appears as brightening features, flows from the east foot-point of F2 to the west, and becomes invisible about 1.1$\times$10^{5} km away. The failed eruption of F1S is triggered by the reconnection, which appears as the brightening threads changing their configuration from crossed to quasiparallel in between the F1S and F3, and is confined by the upper magnetic field. Associated with the eruption, the distant invisible plasma becomes visible as a brightening feature. It continuously flows to the remote foot-point, and becomes invisible before reaching it. The brightening plasma flow outlines the skeleton of FC2 gradually. The observations show the existence of a double-decker FC, as a magnetic structure, before they appear as a brightening/dark feature when fully filled with hot/cool plasma. △ Less

Submitted 26 November, 2025; originally announced November 2025.

Searching for Long-Period Radio Transients in ASKAP EMU Data with 10-Second Imaging

Authors: Yu Wing Joshua Lee, Yuanming Wang, Manisha Caleb, Tara Murphy, Tao An, Barnali Das, Dougal Dobie, Laura N. Driessen, David L. Kaplan, Emil Lenc, Joshua Pritchard, Zorawar Wadiasingh, Zhijun Xu

Abstract: Long-period radio transients (LPTs) are a recently identified phenomenon that challenge our current understanding of compact objects and coherent radio emission mechanisms. These objects emit radio pulses similar to those of pulsars, but at much longer periods -- on the order of minutes to hours. With duty cycles of only a few percent, individual pulses have been observed to last between 10 and 10… ▽ More Long-period radio transients (LPTs) are a recently identified phenomenon that challenge our current understanding of compact objects and coherent radio emission mechanisms. These objects emit radio pulses similar to those of pulsars, but at much longer periods -- on the order of minutes to hours. With duty cycles of only a few percent, individual pulses have been observed to last between 10 and 1000 seconds. This places LPTs in a timescale gap between the two main techniques used in transient radio searches: time-series analysis at millisecond to second timescales, and image-plane searches sensitive to variability on the scale of days. As a result, LPTs remained undetected until recently, and only a handful are currently known. To increase the sample of known LPTs, we conducted a dedicated search using 200 hours of archival data from the ASKAP Evolutionary Map of the Universe survey, covering 750 deg$^2$ of sky at the shortest possible imaging time step of 10-seconds. This represents the first large-scale search using ASKAP data at second-scale resolution. Although no LPTs were detected, we identified flares from six stars, at least one had never been detected in the radio regime before. We placed a lower limit on the transient surface density of $2.21\times10^{-6}$ deg$^{-2}$ at a 10-second timescale, with a sensitivity of 16.9 mJy. Our findings evaluate the feasibility of detecting radio transients using 10-second imaging with ASKAP and provide insights into improving detection pipelines and observation strategies for LPTs. △ Less

Submitted 12 November, 2025; originally announced November 2025.

Comments: 19 pages, 14 figures, 5 tables

Charge-dependent spectral softenings of primary cosmic-rays from proton to iron below the knee

Authors: DAMPE Collaboration, Francesca Alemanno, Qi An, Philipp Azzarello, Felicia-Carla-Tiziana Barbato, Paolo Bernardini, Xiao-Jun Bi, Hugo Valentin Boutin, Irene Cagnoli, Ming-Sheng Cai, Elisabetta Casilli, Jin Chang, Deng-Yi Chen, Jun-Ling Chen, Zhan-Fang Chen, Zi-Xuan Chen, Paul Coppin, Ming-Yang Cui, Tian-Shu Cui, Ivan De Mitri, Francesco de Palma, Adriano Di Giovanni, Tie-Kuang Dong, Zhen-Xing Dong, Giacinto Donvito , et al. (124 additional authors not shown)

Abstract: In most particle acceleration mechanisms, the maximum energy of the cosmic rays can achieve is charge dependent. However, the observational verification of such a fundamental relation is still lack due to the difficulty of measuring the spectra of individual particles from one (kind of) source(s) up to very high energies. This work reports direct measurements of the carbon, oxygen, and iron spectr… ▽ More In most particle acceleration mechanisms, the maximum energy of the cosmic rays can achieve is charge dependent. However, the observational verification of such a fundamental relation is still lack due to the difficulty of measuring the spectra of individual particles from one (kind of) source(s) up to very high energies. This work reports direct measurements of the carbon, oxygen, and iron spectra from ~ 20 gigavolts to ~ 100 teravolts (~ 60 teravolts for iron) with 9 years of on-orbit data collected by the Dark Matter Particle Explorer (DAMPE). Distinct spectral softenings have been directly detected in these spectra for the first time. Combined with the updated proton and helium spectra, the spectral softening appears universally at a rigidity of ~ 15 teravolts. A nuclei mass dependent softening is rejected at a confidence level of > 99.999%. Taking into account the correlated structures at similar energies in the large-scale anisotropies of cosmic rays, one of the most natural interpretations of the spectral structures is the presence of a nearby cosmic ray source. In this case, the softening energies correspond to the acceleration upper limits of such a source, forming the so-called Peters cycle of the spectra. The results thus offer observational verification of the long-standing prediction of the charge-dependent energy limit of cosmic ray acceleration. △ Less

Submitted 10 November, 2025; v1 submitted 7 November, 2025; originally announced November 2025.

Comments: This update corrects typos in the tables

Energy-dependent SEP Fe/O abundances during the May 2024 superstorm

Authors: G. D. Muro, C. M. S. Cohen, Z. Xu, R. A. Leske, A. C. Cummings, S. Bale, G. D. Berland, E. R. Christian, M. E. Cuesta, M. I. Desai, F. Fraschetti, J. Giacalone, L. Y. Khoo, A. Labrador, D. J. McComas, J. G. Mitchell, M. Pulupa, N. A. Schwadron, M. M. Shen

Abstract: During mid-May 2024, active region (AR) 13664 produced a series of M- and X-class flares along with several coronal mass ejections (CMEs) that resulted in exceptionally strong aurora at Earth. This study presents in-situ solar energetic particle (SEP) ion composition data from Solar Terrestrial Relations Observatory Ahead (STA), Advanced Composition Explorer (ACE), and Parker Solar Probe (PSP) as… ▽ More During mid-May 2024, active region (AR) 13664 produced a series of M- and X-class flares along with several coronal mass ejections (CMEs) that resulted in exceptionally strong aurora at Earth. This study presents in-situ solar energetic particle (SEP) ion composition data from Solar Terrestrial Relations Observatory Ahead (STA), Advanced Composition Explorer (ACE), and Parker Solar Probe (PSP) as their magnetic connectivity to AR 13664 varied throughout the event period. Between 08 to 24 May, STA was separated by 12° in longitude from ACE at 0.96 AU. SEP intensities rose gradually due to merged CMEs from AR 13664. On 13 May, an M6 flare was followed by a rapid-onset SEP event at STA, although velocity dispersion analysis yielded no clear path length or release time. PSP, 95° longitudinally separated from Earth at 0.74 AU, observed gradually increasing SEP intensities beginning 11 May, followed by a jump in both SEP intensity and magnetic field (>100 nT) on 16 May. These early event intervals display stepwise SEP increases, consistent with the passage of successive CMEs. On 20 May, an X16.5 flare from AR 13664 produced an Fe-rich SEP event observed at all three spacecraft despite their wide longitudinal separations. Throughout the period, Fe/O ratios ranged from <0.01 to >0.8 and increased with energy between 1 to 100 MeV/nuc. This trend deviates from the typical energy-dependent decrease expected from diffusive shock acceleration and suggests more complex scenarios, possibly involving variable suprathermal seed populations or species-dependent transport. △ Less

Submitted 5 November, 2025; originally announced November 2025.

Comments: 27 pages, 11 figures (2 animations)

Stellar Evolution with Radiative Feedback in AGN Disks

Authors: Zheng-Hao Xu, Yi-Xian Chen, Douglas N. C. Lin

Abstract: Stars embedded in the inner pc region of an active galactic nucleus (AGN) experience extreme accretion conditions that significantly alter their evolution. We present one-dimensional MESA simulations of stars growing and decaying within AGN disks, implementing radiative-feedback-regulated accretion which limits stellar growth near the Eddington luminosity, as well as wind-driven mass loss. Unlike… ▽ More Stars embedded in the inner pc region of an active galactic nucleus (AGN) experience extreme accretion conditions that significantly alter their evolution. We present one-dimensional MESA simulations of stars growing and decaying within AGN disks, implementing radiative-feedback-regulated accretion which limits stellar growth near the Eddington luminosity, as well as wind-driven mass loss. Unlike stand-alone stars in the field, these embedded stars follow unique evolutionary tracks with well-determined mass evolution and chemical yields. We distinguish two regimes: ``immortal" stars that indefinitely remain on the main sequence due to efficient hydrogen mixing; and ``metamorphic" stars that evolves off the main sequence, ultimately enriching the disk with heavy elements upon hydrogen and helium exhaustion in their cores. Results indicate that embedded stars in AGN disks can attain large masses, but gas retention and limited mixing likely render the ``immortal" track unsustainable. We show radiative feedback plays a critical role in preventing runaway growth, since it regulates the inflow to at most of order-unity the Eddington-limited mass-loss rate. Embedded metamorphic stars significantly enrich AGN disks with helium and $α$-elements, potentially explaining the observed high metallicity in broad-line regions (BLR) without excessive helium enrichment. This study underscores the critical interplay between stellar feedback and accretion physics in shaping the stellar populations and chemical evolution within AGN disks. △ Less

Submitted 5 November, 2025; originally announced November 2025.

Comments: Accepted to ApJ

Exploring One-point Statistics in HERA Phase I Data: Effects of Foregrounds and Systematics on Measuring One-Point Statistics

Authors: Honggeun Kim, Jacqueline N. Hewitt, Nicholas S. Kern, Joshua S. Dillon, Kai-Feng Chen, Zhilei Xu, Eleanor Rath, Vincent MacKay, Tyrone Adams, James E. Aguirre, Rushelle Baartman, Adam P. Beardsley, Gianni Bernardi, Tashalee S. Billings, Judd D. Bowman, Richard F. Bradley, Philip Bull, Jacob Burba, Steven Carey, Chris L. Carilli, David R. DeBoer, Eloy de Lera Acedo, Matt Dexter, Nico Eksteen, John Ely , et al. (39 additional authors not shown)

Abstract: Measuring one-point statistics in redshifted 21 cm intensity maps offers an opportunity to explore non-Gaussian features of the early universe. We assess the impact of instrumental effects on measurements made with the Hydrogen Epoch of Reionization Array (HERA) by forward modeling observational and simulation data. Using HERA Phase I observations over 94 nights, we examine the second (m2, varianc… ▽ More Measuring one-point statistics in redshifted 21 cm intensity maps offers an opportunity to explore non-Gaussian features of the early universe. We assess the impact of instrumental effects on measurements made with the Hydrogen Epoch of Reionization Array (HERA) by forward modeling observational and simulation data. Using HERA Phase I observations over 94 nights, we examine the second (m2, variance) and third (m3) moments of images. We employ the DAYENU-filtering method for foreground removal and reduce simulated foreground residuals to 10% of the 21 cm signal residuals. In noiseless cosmological simulations, the amplitudes of one-point statistics measurements are significantly reduced by the instrument response and further reduced by wedge-filtering. Analyses with wedge-filtered observational data, along with expected noise simulations, show that systematics alter the probability distribution of the map pixels. Likelihood analysis based on the observational data shows m2 measurements disfavor the cold reionization model characterized by inefficient X-ray heating, in line with other power spectra measurements. Small signals in m3 due to the instrument response of the Phase I observation and wedge-filtering make it challenging to use these non-Gaussian statistics to explore model parameters. Forecasts with the full HERA array predict high signal-to-noise ratios for m2, m3, and S3 assuming no foregrounds, but wedge-filtering drastically reduces these ratios. This work demonstrates conclusively that a comprehensive understanding of instrumental effects on m2 and m3 is essential for their use as a cosmological probe, given their dependence on the underlying model. △ Less

Submitted 3 November, 2025; originally announced November 2025.

Comments: 29 pages, 18 figures

Journal ref: ApJ, 993, 189 (2025)

A Star's Death by a Thousand Cuts: The Runaway Periodic Eruptions of AT2023uqm

Authors: Yibo Wang, Tingui Wang, Shifeng Huang, Jiazheng Zhu, Ning Jiang, Wenbin Lu, Rongfeng Shen, Shiyan Zhong, Dong Lai, Yi Yang, Xinwen Shu, Tianyu Xia, Di Luo, Jianwei Lyu, Thomas Brink, Alex Filippenko, Weikang Zheng, Minxuan Cai, Zelin Xu, Mingxin Wu, Xiaer Zhang, Weiyu Wu, Lulu Fan, Ji-an Jiang, Xu Kong , et al. (15 additional authors not shown)

Abstract: Stars on bound orbits around a supermassive black hole may undergo repeated partial tidal disruption events (rpTDEs), producing periodic flares. While several candidates have been suggested, definitive confirmation of these events remains elusive. We report the discovery of AT2023uqm, a nuclear transient that has exhibited at least five periodic optical flares, making it only the second confirmed… ▽ More Stars on bound orbits around a supermassive black hole may undergo repeated partial tidal disruption events (rpTDEs), producing periodic flares. While several candidates have been suggested, definitive confirmation of these events remains elusive. We report the discovery of AT2023uqm, a nuclear transient that has exhibited at least five periodic optical flares, making it only the second confirmed case of periodicity after ASASSN-14ko. Uniquely, the flares from AT2023uqm show a nearly exponential increase in energy--a "runaway" phenomenon signaling the star's progressive destruction. This behavior is consistent with rpTDEs of low-mass, main-sequence stars or evolved giant stars. Multiwavelength observations and spectroscopic analysis of the two most recent flares reinforce its interpretation as an rpTDE. Intriguingly, each flare displays a similar double-peaked structure, potentially originating from a double-peaked mass fallback rate or two discrete collisions per orbit. The extreme ratio of peak separation to orbital period draws attention to the possibility of a giant star being disrupted, which could be distinguished from a low-mass main-sequence star by its future mass-loss evolution. Our analysis demonstrates the power of rpTDEs to probe the properties of disrupted stars and the physical processes of tidal disruption, though it is currently limited by our knowledge of these events. AT2023uqm emerges as the most compelling rpTDE thus far, serving as a crucial framework for modeling and understanding these phenomena. △ Less

Submitted 30 October, 2025; v1 submitted 30 October, 2025; originally announced October 2025.

Comments: Submitted. Comments are welcome

Magnetic Field Configuration of a Quiescent Prominence Revealed by Large-amplitude Longitudinal Oscillations in End-view Observations

Authors: Jun Dai, Ayumi Asai, Dechao Song, Ye Qiu, Zhe Xu

Abstract: Prominence seismology, applied to the large-amplitude longitudinal oscillation, is used to indirectly diagnose the geometry and strength of the magnetic fields inside the prominence. In this paper, combining imaging and spectroscopic data, the magnetic field configuration of a quiescent prominence is revealed by large-amplitude longitudinal oscillations observed in end view on 2023 December 4. Par… ▽ More Prominence seismology, applied to the large-amplitude longitudinal oscillation, is used to indirectly diagnose the geometry and strength of the magnetic fields inside the prominence. In this paper, combining imaging and spectroscopic data, the magnetic field configuration of a quiescent prominence is revealed by large-amplitude longitudinal oscillations observed in end view on 2023 December 4. Particularly, the prominence oscillation involved blueshift velocities in Dopplergrams and horizontal motions in extreme-ultraviolet (EUV) images. Originally, the prominence oscillation was triggered by the collision and heating of an adjoining hot structure associated with two coronal jets. The oscillation involved two groups of signals with similar oscillatory parameters, a three-dimensional (3D) initial amplitude of 40 Mm and a 3D velocity amplitude of 48 km/s, both lasting for 4 cycles with a period of 77 minutes, with a phase difference of pi/4. While the angle between 3D velocities and the prominence axis ranges from 10 to 30. Two methods, utilizing time-distance diagrams and velocity fields, are employed to calculate the curvature radius of magnetic dips supporting the prominence materials. Both methods yield similar value ranges and trends from the bottom to the top of magnetic dips, with the curvature radius increasing from 90 Mm to 220 Mm, then decreasing to 10 Mm, with transverse magnetic field strength 25 Gauss. From this, the realistic 3D geometry of the prominence magnetic dips is determined to be sinusoidal. To the best of our knowledge, we present the first accurate calculation of the 3D curvature radius and geometry of the prominence magnetic dips based on longitudinal oscillatory motions. △ Less

Submitted 24 October, 2025; originally announced October 2025.

Comments: 18 pages, 7 figures

Local Particle Acceleration in an ICME-in-Sheath Structure Observed by Solar Orbiter

Authors: Xiaomin Chen, Chuan Li, Zigong Xu, Georgios Nicolaou, Alexander Kollhoff, George C. Ho, Robert F. Wimmer-Schweingruber, Christopher J. Owen

Abstract: Local particle acceleration in the shock sheath region formed during the interaction between multiple coronal mass ejections (CMEs) is a complicated process that is still under investigation. On March 23, 2024, the successive eruption of two magnetic flux ropes (MFRs) from the solar active region 3614 produced twin CMEs, as identified in coronagraph images. By analyzing in-situ data from Solar Orb… ▽ More Local particle acceleration in the shock sheath region formed during the interaction between multiple coronal mass ejections (CMEs) is a complicated process that is still under investigation. On March 23, 2024, the successive eruption of two magnetic flux ropes (MFRs) from the solar active region 3614 produced twin CMEs, as identified in coronagraph images. By analyzing in-situ data from Solar Orbiter and Wind, it is found that the primary ICME-driven shock overtook the preceding ICME, trapping it in the sheath between the shock and the primary ICME, forming the ICME-in-sheath (IIS) structure. Using Solar Orbiter observations, we show that both electrons and ions are accelerated within the IIS. A clear enhancement of suprathermal electrons was observed at the IIS boundary, where strong flow shear and large magnetic field variation suggest possible local electron acceleration. Electrons (>38 keV) exhibit a long-lasting enhancement in the IIS with a spectral index of ~2.2, similar to that in the shock sheath and the primary ICME, indicating a similar solar origin. Inside both the sheath and IIS, spectra of proton and 4He are generally consistent with the prediction of the diffusive shock acceleration, whereas Fe and O present a double power-law shape. Additionally, the Fe/O ratio in the IIS is higher than that in the sheath, and more close to the abundance of the flare-related particles, suggesting the remnant particles of flare confined in the IIS. △ Less

Submitted 16 October, 2025; originally announced October 2025.

Comments: 14 pages, 6 figures, accepted for publication in ApJ

Observational study of chromospheric jets in and around a sunspot observed by NVST and SDO

Authors: Guotang Wu, Xiaoli Yan, Zhike Xue, Jincheng Wang, Zhe Xu, Liheng Yang, Yian Zhou, Liping Yang, Xinsheng Zhang, Qifan Dong, Zongyin Wu

Abstract: To better understand the characteristics, driving mechanisms, and potential heating contributions of chromospheric jets, we analyze two contrasting types: one originating from within the sunspot penumbra (inside jets), and the other originating from outside the penumbra (outside jets). Statistical analysis of 100 jets (50 inside jets and 50 outside jets) reveals that inside jets have a projected v… ▽ More To better understand the characteristics, driving mechanisms, and potential heating contributions of chromospheric jets, we analyze two contrasting types: one originating from within the sunspot penumbra (inside jets), and the other originating from outside the penumbra (outside jets). Statistical analysis of 100 jets (50 inside jets and 50 outside jets) reveals that inside jets have a projected velocity range of 4--14~km\,s$^{-1}$, a length range of 1--4~Mm, a width range of 0.2--0.6~Mm, and a lifetime range of 135--450~s, with mean values of 7.90~km\,s$^{-1}$, 2.61~Mm, 0.41~Mm, and 260~s, respectively. About 52\% of inside jets are associated with brightenings in H$α$ blue wing images, and some show high-temperature signatures, suggesting a connection with localized energy release. In contrast, outside jets have higher velocities (8--50~km\,s$^{-1}$, average 19.04~km\,s$^{-1}$), greater lengths (average 6.26~Mm, up to 27.27~Mm), slightly larger widths (average 0.46~Mm), and longer lifetimes (135--630~s, average 327~s). They typically originate from regions of opposite magnetic polarities and are associated with magnetic flux emergence and EUV brightenings. Some outside jets correspond to coronal jets with inverted Y-shaped structures and temperatures exceeding one million Kelvin. Our results suggest that both jet types are driven by magnetic reconnection occurring in distinct magnetic field configurations and contribute to chromospheric and coronal heating. △ Less

Submitted 13 October, 2025; originally announced October 2025.

Comments: 18 pages, 11 figures, accepted for publication in ApJ

Properties of Chromospheric Fibrils Around a Quiescent Filament

Authors: Qifan Dong, Xiaoli Yan, Zhike Xue, Jincheng Wang, Zhe Xu, Liheng Yang, Yian Zhou, Xinsheng Zhang, Zongyin Wu, Guotang Wu

Abstract: Fibrils are dynamic plasma structures in the solar chromosphere. Studying these structures is critical for understanding solar atmospheric heating and mass transportation. The purpose of this study is to obtain the characteristics of fibrils surrounding the filament. By employing high-resolution H-alpha data obtained from the New Vacuum Solar Telescope (NVST), we undertake a detailed analysis of t… ▽ More Fibrils are dynamic plasma structures in the solar chromosphere. Studying these structures is critical for understanding solar atmospheric heating and mass transportation. The purpose of this study is to obtain the characteristics of fibrils surrounding the filament. By employing high-resolution H-alpha data obtained from the New Vacuum Solar Telescope (NVST), we undertake a detailed analysis of the properties of 63 fibrils situated in the vicinity of the filament. Comparing the fibrils on both sides of the filament demonstrates that these fibrils have similar physical properties except for their orientation. The properties of fibrils are statistically measured, including lifetimes of 150-650 s, widths of 320-850 km, maximum lengths of 3-8.5 Mm, projection velocities of 7-29 km/s, and decelerations of 45-474 m/s2. The dominant oscillation period of fibrils is predominantly concentrated in the range of 4.8-6.6 minutes (2.5-3.5 mHz). Transverse oscillations are identified in a subset of fibrils, with periodicities of 269-289 s and phase speeds of 13.7-25.8 km/s, indicating the presence of kink-mode magnetohydrodynamic (MHD) waves. △ Less

Submitted 23 September, 2025; originally announced September 2025.

Comments: 10 pages, 7 figures, accepted for publication in MNRAS

Investigation of hadronic cross sections of cosmic ray carbon and oxygen on BGO from 200 GeV to 10 TeV energy at the DAMPE experiment

Authors: F. Alemanno, Q. An, P. Azzarello, F. C. T. Barbato, P. Bernardini, X. J. Bi, H. Boutin, I. Cagnoli, M. S. Cai, E. Casilli, E. Catanzani, J. Chang, D. Y. Chen, J. L. Chen, Z. F. Chen, Z. X. Chen, P. Coppin, M. Y. Cui, T. S. Cui, Y. X. Cui, I. De Mitri, F. de Palma, A. Di Giovanni, T. K. Dong, Z. X. Dong , et al. (122 additional authors not shown)

Abstract: The Dark Matter Particle Explorer (DAMPE) has made significant progress in measuring the fluxes of cosmic rays. These new measurements are pivotal in advancing our understanding of the origins and propagation mechanisms of cosmic rays. The bismuth germanium oxide (BGO) calorimeter plays a crucial role in these measurements, particularly in the precise determination of cosmic ray fluxes. However, f… ▽ More The Dark Matter Particle Explorer (DAMPE) has made significant progress in measuring the fluxes of cosmic rays. These new measurements are pivotal in advancing our understanding of the origins and propagation mechanisms of cosmic rays. The bismuth germanium oxide (BGO) calorimeter plays a crucial role in these measurements, particularly in the precise determination of cosmic ray fluxes. However, for a calorimetric experiment like DAMPE, uncertainties in hadronic models persist as a major barrier in achieving more accurate measurements of fluxes of cosmic ray nuclei. This study centers on the measurement of the inelastic hadronic cross sections of carbon and oxygen nuclei interacting with BGO crystals target over an extensive energy range, spanning from 200 GeV to 10 TeV. For carbon nuclei interacting with the BGO target, the measurements of the cross sections have achieved a total relative uncertainty of less than 10% below 8 TeV for carbon, and below 3 TeV for oxygen. For oxygen nuclei, the same level of precision was attained below 3 TeV. Additionally, we compare the experimental results with Geant4 and FLUKA simulations to validate the accuracy and consistency of these simulation tools. Through comprehensive analysis of the inelastic hadronic interaction cross sections, this research provides validation for the hadronic interaction models used in DAMPE's cosmic-ray flux measurements. △ Less

Submitted 21 September, 2025; originally announced September 2025.

Complete Sampling of the $uv$ Plane with Realistic Radio Arrays: Introducing the RULES Algorithm, with Application to 21 cm Foreground Wedge Removal

Authors: Vincent MacKay, Zhilei Xu, Ruby Byrne, Jacqueline Hewitt

Abstract: We introduce the Radio-array $uv$ Layout Engineering Strategy (RULES), an algorithm for designing radio arrays that achieve complete coverage of the $uv$ plane, defined as, at minimum, regular sampling at half the observing wavelength ($λ$) along the $u$ and $v$ axes within a specified range of baseline lengths. Using RULES, we generate $uv$-complete layouts that cover the range… ▽ More We introduce the Radio-array $uv$ Layout Engineering Strategy (RULES), an algorithm for designing radio arrays that achieve complete coverage of the $uv$ plane, defined as, at minimum, regular sampling at half the observing wavelength ($λ$) along the $u$ and $v$ axes within a specified range of baseline lengths. Using RULES, we generate $uv$-complete layouts that cover the range $10λ\leq|(u,v)|\leq 100λ$ with fewer than 1000 antennas of diameter $5λ$, comparable to current and planned arrays. We demonstrate the effectiveness of such arrays for mitigating contamination from bright astrophysical foregrounds in 21 cm Epoch of Reionization observations,particularly in the region of Fourier space known as the foreground wedge,by simulating visibilities of foreground-like sky models over the 130-150 MHz band and processing them through an image-based power spectrum estimator. We find that with complete $uv$ coverage, the wedge power is suppressed by sixteen orders of magnitude compared to an array with a compact hexagonal layout (used as a reference for a sparse $uv$ coverage). In contrast, we show that an array with the same number of antennas but in a random configuration only suppresses the wedge by three orders of magnitude, despite sampling more distinct $uv$ points over the same range. We address real-world challenges and find that our results are sensitive to small antenna position errors and missing baselines, while still performing equally or significantly better than random arrays in any case. We propose ways to mitigate those challenges such as a minimum redundancy requirement or tighter $uv$ packing density. △ Less

Submitted 18 September, 2025; originally announced September 2025.

Comments: 23 pages, 17 figures

Charged Loops at the Cosmological Collider with Chemical Potential

Authors: Arushi Bodas, Edward Broadberry, Raman Sundrum, Zhaohui Xu

Abstract: Cosmological collider physics allows the detection of heavy particles at inflationary scales through their imprints on primordial non-Gaussianities. We study the chemical potential mechanism applied to a pair of charged scalars. We analytically evaluate the resulting one-loop contribution to the bispectrum, using the spectral decomposition. In this way we are able to determine the parametric depen… ▽ More Cosmological collider physics allows the detection of heavy particles at inflationary scales through their imprints on primordial non-Gaussianities. We study the chemical potential mechanism applied to a pair of charged scalars. We analytically evaluate the resulting one-loop contribution to the bispectrum, using the spectral decomposition. In this way we are able to determine the parametric dependences for both the signal and the background. We show that a signal strength $f_{\mathrm{NL}}\sim O(0.01)$ can be obtained within theoretical control, potentially reachable by 21cm tomography. As an application we consider the colored Higgs bosons in $\mathrm{SU}(5)$ supersymmetric orbifold grand unification with masses $M\lesssim10^{15}\:\mathrm{GeV}$. △ Less

Submitted 30 July, 2025; originally announced July 2025.

Comments: 69 pages, 23 figures

Report number: FERMILAB-PUB-25-0519-V

A Common Origin of Normal Type Ia Supernovae Suggested by the Photometric Diversity

Authors: Weiyu Wu, Ji-an Jiang, Dezheng Meng, Zelin Xu, Keiichi Maeda, Mamoru Doi, Ken'ichi Nomoto, Naoki Yasuda, Masaomi Tanaka, Toshikazu Shigeyama, Nozomu Tominaga, Željko Ivezić, Peter Yoachim, Saurabh W. Jha, Tinggui Wang, Nao Suzuki, Hisanori Furusawa, Andrew J. Connolly, Satoshi Miyazaki

Abstract: In recent years, with an increasing number of type Ia supernovae (SNe Ia) discovered soon after their explosions, a non-negligible fraction of SNe Ia with early-excess emissions (EExSNe Ia) have been confirmed. In this letter, we present a total of \textbf{67} early-phase normal SNe Ia from published papers and ongoing transient survey projects to systematically investigate their photometric behav… ▽ More In recent years, with an increasing number of type Ia supernovae (SNe Ia) discovered soon after their explosions, a non-negligible fraction of SNe Ia with early-excess emissions (EExSNe Ia) have been confirmed. In this letter, we present a total of \textbf{67} early-phase normal SNe Ia from published papers and ongoing transient survey projects to systematically investigate their photometric behaviors from very early time. We found that EExSNe Ia in our sample have longer rise and brighter peak luminosities compared to those of non-EExSNe Ia. Moreover, EExSNe Ia commonly have ``red-bump" features in the early $B-V$ color while non-EExSNe Ia show blueward evolution from the very beginning. Here, we propose that the thin-helium double-detonation scenario can phenomenologically explain the photometric diversities of normal SNe Ia considering different white dwarf-He-shell mass combinations and the viewing-angle effect, implying a unified explosion mechanism of normal-type SNe Ia. To further testify the possible common origin of normal SNe Ia, systematical studies of multiband photometric and spectral properties of early-phase SNe Ia through the new generation wide-field time-domain survey facilities and global real-time follow-up networks are highly demanded. △ Less

Submitted 21 July, 2025; originally announced July 2025.

Comments: 17 pages, 6 figures, and 1 table, accepted for publication in ApJ

Interpreting Hubble tension with a cascade decaying dark matter sector

Authors: Quan Zhou, Zixuan Xu, Sibo Zheng

Abstract: Hubble tension can be alleviated by altering either early- or late-time $Λ$CDM. So far, extensive studies have shown that only early dark energy or ad hoc combinations of those two-fold effects can reduce the tension to $3σ$ level or lower. In this work, we improve the latter solution by considering a cascade decaying dark matter sector, where a parent particle produces relativistic dark matter in… ▽ More Hubble tension can be alleviated by altering either early- or late-time $Λ$CDM. So far, extensive studies have shown that only early dark energy or ad hoc combinations of those two-fold effects can reduce the tension to $3σ$ level or lower. In this work, we improve the latter solution by considering a cascade decaying dark matter sector, where a parent particle produces relativistic dark matter in the early Universe and the dark matter subsequently decays to neutrinos in the late-time Universe. We parametrize this model with four model parameters, carry out a Markov Chain Monte Carlo fit to Planck 2018+BAO+Pantheon data sets, and compare it to Big Bang Nucleosynthesis limits, neutrino flux bounds, Planck data about matter power spectrum, and structure formation constraint. Within parameter regions reducing the Hubble tension to $3.2σ$ and compatible with the existing constraints, the main phenomenological features include a larger $S_{8}\sim 0.84$, smaller $n_{s}\sim 0.95$ and larger matter power spectrum relative to the $Λ$CDM, which are left for future tests. △ Less

Submitted 11 November, 2025; v1 submitted 11 July, 2025; originally announced July 2025.

Comments: 18 pages, 5 figures; v2: typos corrected, added discussion and references

Influence of interstellar environment near the solar system on cosmic-ray spectra and dipole anisotropy

Authors: Zhangxi Xue, Siming Liu

Abstract: Properties of interstellar environment near the solar system have been probed by missions like IBEX, Voyager over the last two decades. Although it has been well recognized that properties of cosmic rays up to the PeV energy can be affected by the local interstellar environment, detailed modeling has not been done. We show that a three component model for the cosmic ray proton and helium spectra f… ▽ More Properties of interstellar environment near the solar system have been probed by missions like IBEX, Voyager over the last two decades. Although it has been well recognized that properties of cosmic rays up to the PeV energy can be affected by the local interstellar environment, detailed modeling has not been done. We show that a three component model for the cosmic ray proton and helium spectra from GV to several PV can naturally explain the energy dependence of the dipole anisotropy of cosmic ray fluxes by considering effects of the local interstellar environment on cosmic ray transport, addressing the so-called cosmic ray anisotropy problem. In particular, it is shown that the dipole amplitude and position angle below $\sim 100$ TeV are very sensitive to the velocity of the heliosphere in the local interstellar cloud and the motion of the local interstellar cloud in the local standard of rest. Better measurement of cosmic ray flux anisotropy by experiments like LHAASO and properties of the local interstellar environment by future missions like IMAP will be able to test this model. △ Less

Submitted 9 July, 2025; originally announced July 2025.

Comments: link to the online abstract in the APS journal: https://link.aps.org/doi/10.1103/19cr-tyrb

Journal ref: Phys. Rev. D 111, 123036 (2025)

Scrutinizing the impact of the solar modulation on AMS-02 antiproton excess

Authors: Kai-Kai Duan, Xiao Wang, Wen-Hao Li, Zhi-Hui Xu, Yue-Lin Sming Tsai, Yi-Zhong Fan

Abstract: This study examines the impact of solar modulation on the antiproton excess observed by AMS-02, which may indicate dark matter (DM) annihilation. We analyze three solar modulation models: the force-field approximation (FFA), a time-, charge-, and rigidity-dependent FFA, and a three-dimensional numerical simulation based on the Parker transport equation. Based on AMS-02 latest antiproton data (2025… ▽ More This study examines the impact of solar modulation on the antiproton excess observed by AMS-02, which may indicate dark matter (DM) annihilation. We analyze three solar modulation models: the force-field approximation (FFA), a time-, charge-, and rigidity-dependent FFA, and a three-dimensional numerical simulation based on the Parker transport equation. Based on AMS-02 latest antiproton data (2025), our results show that the significance of the DM signal is sensitive to the chosen modulation model, with a 2$σ$ signal for the FFA (4$σ$ if including data from H, He, C, O, B/C, and B/O) and a reduced significance for more complex models. We also address systematic uncertainties using two methods: the add-in-quadrature method, which assumes uncorrelated uncertainties between energy bins, and the nuisance parameter method, which treats systematic uncertainties as nuisance parameters during the fitting process. Fitted to AMS-02 antiproton data, DM annihilation to the $b\bar{b}$ scenario with three different solar modulation models shows that the add-in-quadrature method causes overfitting, whereas the nuisance parameters approach leads to underfitting. Statistically, the signal region of the FFA model using the add-in-quadrature method is the most reliable. This work highlights the need for refined solar modulation models and a better treatment of uncertainties for a conclusive interpretation of the AMS-02 data. △ Less

Submitted 10 October, 2025; v1 submitted 16 June, 2025; originally announced June 2025.

Comments: 23 pages, 9 figures, accepted for publication in JCAP

Pulsar Sparking: What if mountains on the surface?

Authors: Zi-Hao Xu, Wei-Yang Wang, Shun-Shun Cao, Ren-Xin Xu

Abstract: A numerical framework to calculate the height and potential of the vacuum inner gap of pulsars is presented here. % The results demonstrate that small mountains on a pulsar's polar cap tend to significantly influence the properties of the inner vacuum gap, making it easier for sparks to form. % In this scenario, the magnetospheric activity observed from the pulsars PSR J0250$+$5854 and PSR J2144… ▽ More A numerical framework to calculate the height and potential of the vacuum inner gap of pulsars is presented here. % The results demonstrate that small mountains on a pulsar's polar cap tend to significantly influence the properties of the inner vacuum gap, making it easier for sparks to form. % In this scenario, the magnetospheric activity observed from the pulsars PSR J0250$+$5854 and PSR J2144$-$3933 which lie below the traditional pulsar death line, and some single-pulse modulation phenomena could also then be understood. % Furthermore, the presence of small mountains should depend on the puzzling state of supranuclear matter inside pulsars. % In order to sustain stable mountains on the surface, pulsars might be made of solid strangeon matter, which is favoured by both the charge neutrality and the flavour symmetry of quarks. △ Less

Submitted 11 December, 2025; v1 submitted 13 June, 2025; originally announced June 2025.

Comments: 15 pages, 6 figures, RAA accepted

High-resolution Observations of a C9.3 White-light Flare and Its Impact on the Solar Photosphere

Authors: Zhe Xu, Xiaoli Yan, Zhentong Li, Liheng Yang, Zhike Xue, Jincheng Wang, Yian Zhou

Abstract: We present a detailed analysis of a C9.3 white-light flare using high-resolution observations from the New Vacuum Solar Telescope (NVST). The flare occurred near the eastern solar limb on September 11, 2023, within NOAA AR 13431, and produced beam electrons with energies just below 50 keV as observed by the the Hard X-ray Imager (HXI) onboard the Advanced Space-based Solar Observatory (ASO-S). Two… ▽ More We present a detailed analysis of a C9.3 white-light flare using high-resolution observations from the New Vacuum Solar Telescope (NVST). The flare occurred near the eastern solar limb on September 11, 2023, within NOAA AR 13431, and produced beam electrons with energies just below 50 keV as observed by the the Hard X-ray Imager (HXI) onboard the Advanced Space-based Solar Observatory (ASO-S). Two white-light flare kernels were detected in the TiO band, connected by filamentary brightenings aligned with penumbral fibrils, suggesting a photospheric contribution to the white-light emission. Notably, the impact of the flare on the solar photosphere was characterized by sudden vortex flows and significant amplification of magnetic field in the white-light flare kernel region. We infer that this impact is driven by the propagation of flare-generated Alfvén wave pulses, which deposited energy into the photosphere. These observations support the potential role of the Alfvén wave mechanism in driving energy transport and heating during white-light flares. △ Less

Submitted 9 June, 2025; originally announced June 2025.

The Observations of Magnetic Reconnection During the Interaction Process of Two Active Region Filaments

Authors: Zongyin Wu, Zhike Xue, Xiaoli Yan, Jincheng Wang, Liheng Yang, Zhe Xu, Qiaoling Li, Yang Peng, Liping Yang, Yian Zhou, Xinsheng Zhang, Liufan Gong, Qifan Dong, Guotang Wu

Abstract: We investigate the interaction between two filaments (F1 and F2) and their subsequent magnetic reconnection in active region (AR) NOAA 13296 and AR NOAA 13293 on May 9, 2023, utilizing high spatial and temporal resolution and multi-wavelength observational data from the Solar Dynamics Observatory, the New Vacuum Solar Telescope, and the Chinese Hα Solar Explorer. The movement of F1 from the southe… ▽ More We investigate the interaction between two filaments (F1 and F2) and their subsequent magnetic reconnection in active region (AR) NOAA 13296 and AR NOAA 13293 on May 9, 2023, utilizing high spatial and temporal resolution and multi-wavelength observational data from the Solar Dynamics Observatory, the New Vacuum Solar Telescope, and the Chinese Hα Solar Explorer. The movement of F1 from the southeast toward the northwest, driven by the motion of the positive magnetic polarity (P1), leads to a collision and reconnection with F2. This reconnection exchanges their footpoints, resulting in the formation of two new filaments (F3 and F4) consistent with "slingshot" type filament interaction. During the interaction, the current sheet moving due to the motion of F1 and the reconnection outflows moving along F3 and F4 were both observed. The current sheet is rarely observed in the slingshot type filament interaction, measuring approximately 2.17 Mm in length and 0.84 Mm in width. After the interaction, the F1 disappears whereas a portion of F2 remains, indicating that the interaction involves partial slingshot reconnection, due to the unequal magnetic flux between the filaments. The residual part of F2 will undergo another magnetic reconnection in the same interaction region with the magnetic loops connecting polarities N1 and P1. The material generated by the reconnection is continuously injected into F4, leading to its final morphology. The findings enhance our understanding of slingshot-type filament interactions, indicating that partial slingshot reconnections between filaments may be more common than full slingshot events. △ Less

Submitted 5 June, 2025; originally announced June 2025.

Comments: 16 pages, 7 figures

Journal ref: ApJ 984 4 (2025)

The Chinese Pulsar Timing Array data release I. Single pulsar noise analysis

Authors: Siyuan Chen, Heng Xu, Yanjun Guo, Bojun Wang, R. Nicolas Caballero, Jinchen Jiang, Jiangwei Xu, Zihan Xue, Kejia Lee, Jianping Yuan, Yonghua Xu, Jingbo Wang, Longfei Hao, Jintao Luo, Jinlin Han, Peng Jiang, Zhiqiang Shen, Min Wang, Na Wang, Renxin Xu, Xiangping Wu, Lei Qian, Xin Guan, Menglin Huang, Chun Sun , et al. (1 additional authors not shown)

Abstract: The Chinese Pulsar Timing Array (CPTA) has collected observations from 57 millisecond pulsars using the Five-hundred-meter Aperture Spherical Radio Telescope (FAST) for close to three years, for the purpose of searching for gravitational waves (GWs). To robustly search for ultra-low-frequency GWs, pulsar timing arrays (PTAs) need to use models to describe the noise from the individual pulsars. We… ▽ More The Chinese Pulsar Timing Array (CPTA) has collected observations from 57 millisecond pulsars using the Five-hundred-meter Aperture Spherical Radio Telescope (FAST) for close to three years, for the purpose of searching for gravitational waves (GWs). To robustly search for ultra-low-frequency GWs, pulsar timing arrays (PTAs) need to use models to describe the noise from the individual pulsars. We report on the results from the single pulsar noise analysis of the CPTA data release I (DR1). Conventionally, power laws in the frequency domain are used to describe pulsar red noise and dispersion measurement (DM) variations over time. Employing Bayesian methods, we found the choice of number and range of frequency bins with the highest evidence for each pulsar individually. A comparison between a dataset using DM piecewise measured (DMX) values and a power-law Gaussian process to describe the DM variations shows strong Bayesian evidence in favour of the power-law model. Furthermore, we demonstrate that the constraints obtained from four independent software packages are very consistent with each other. The short time span of the CPTA DR1, paired with the large sensitivity of FAST, has proved to be a challenge for the conventional noise model using a power law. This mainly shows in the difficulty to separate different noise terms due to their covariances with each other. Nineteen pulsars are found to display covariances between the short-term white noise and long-term red and DM noise. With future CPTA datasets, we expect that the degeneracy can be broken. Finally, we compared the CPTA DR1 results against the noise properties found by other PTA collaborations. While we can see broad agreement, there is some tension between different PTA datasets for some of the overlapping pulsars. This could be due to the differences in the methods and frequency range compared to the other PTAs. △ Less

Submitted 5 June, 2025; originally announced June 2025.

Comments: 17 pages, 4 figures, 10 tables

A Silicon Microstrip Detector for Power-Limited and Large Sensitive Area Applications

Authors: Dexing Miao, Zijun Xu, Zhiyu Xiang, Pingcheng Liu, Giovanni Ambrosi, Mattia Barbanera, Mengke Cai, Xudong Cai, Hsin-Yi Chou, Matteo Duranti, Valerio Formato, Maria Ionica, Yaozu Jiang, Liangchenglong Jin, Vladimir Koutsenko, Qinze Li, Cong Liu, Xingjian Lv, Alberto Oliva, Wenxi Peng, Rui Qiao, Gianluigi Silvestre, Zibing Wu, Xuhao Yuan, Hongyu Zhang , et al. (2 additional authors not shown)

Abstract: A silicon microstrip detector (SSD) has been developed to have state of the art spatial resolution and a large sensitive area under stringent power constraints. The design incorporates three floating strips with their bias resistors inserted between two aluminum readout strips. Beam test measurements with the single sensor confirmed that this configuration achieves a total detection efficiency of… ▽ More A silicon microstrip detector (SSD) has been developed to have state of the art spatial resolution and a large sensitive area under stringent power constraints. The design incorporates three floating strips with their bias resistors inserted between two aluminum readout strips. Beam test measurements with the single sensor confirmed that this configuration achieves a total detection efficiency of $99.8 \, \%$ and spatial resolution $7.6 \, \mathrm{μm}$ for MIPs. A double-$η$ algorithm was developed to optimize hit position reconstruction for this SSD. The design can be adapted for large area silicon detectors. △ Less

Submitted 28 May, 2025; originally announced May 2025.

Comments: 9 pages, 13 figures

Recurrent Jetlets Associated with the Disappearance of a Satellite Spot

Authors: Liheng Yang, Xiaoli Yan, Jun Zhang, Zhike Xue, Zhe Xu, Jincheng Wang, Yijun Hou, Yian Zhou, Defang Kong, Roslan Umar, Xinsheng Zhang, Qiaoling Li, Liping Yang

Abstract: Recurrent small-scale eruptions are fascinating phenomena in the solar atmosphere. However, their underlying physical mechanisms remain unclear. On 2021 May 23, five recurrent jetlets (J1-J5) were observed continuously ejecting from a satellite spot located at the north edge of AR 12824. Using high-resolution, multi-wavelength data from NVST, SDO, and IRIS, we investigate the physical characterist… ▽ More Recurrent small-scale eruptions are fascinating phenomena in the solar atmosphere. However, their underlying physical mechanisms remain unclear. On 2021 May 23, five recurrent jetlets (J1-J5) were observed continuously ejecting from a satellite spot located at the north edge of AR 12824. Using high-resolution, multi-wavelength data from NVST, SDO, and IRIS, we investigate the physical characteristics of these jetlets and their relationship with the satellite spot. The widths of these jetlets range from 1300 to 2900 km, their lifetimes range span 3 to 10 minutes, and their projection speeds vary from 152.8 to 406.0 km s$^{-1}$. During the eruptions, the satellite spot moved northwest at a low speed of 376 $\pm$ 12 m s$^{-1}$. Its area gradually decreased due to magnetic cancellation with surrounding positive magnetic field, resulting in an average cancellation rate of 1.3$\times$10$^{18}$ Mx hr$^{-1}$. Dark lanes that separated from the satellite spot and small pores were observed to move toward nearby these features or dark lanes with opposite polarities, eventually disappearing during the magnetic cancellation process. J4 was driven by an eruption of a micro-filament. Spectral observations revealed a redshift on the right side of J4 and a blueshift on the left side of its base, suggesting a counterclockwise rotation. The horizontal magnetic field of the satellite spot consistently exhibited a vortex structure throughout its evolution until it vanished. The nonlinear force-free field extrapolation confirms that the satellite spot serves as one footpoint of a mini-flux rope. These observations reveal that these jetlets might result from three-dimensional null-point magnetic reconnection, initiated by the continuous eruption of a mini-flux-rope or multiple mini-flux-ropes, driven by sustained magnetic cancellation. △ Less

Submitted 16 May, 2025; originally announced May 2025.

Comments: 22 pages, 9 figures, accepted for publication in The Astrophysical Journal

Periodic variation of magnetoionic environment of a fast radio burst source

Authors: Jiangwei Xu, Heng Xu, Yanjun Guo, Jinchen Jiang, Bojun Wang, Zihan Xue, Yunpeng Men, Kejia Lee, Bing Zhang, Weiwei Zhu, Jinlin Han

Abstract: Fast radio bursts (FRBs) are luminous, dispersed millisecond-duration radio bursts whose origin is poorly known. Recent observations suggest that some FRBs may reside in binary systems, even though conclusive evidence remains elusive. Here we report the detection of a 26.24$\pm$0.02 day periodicity in Faraday rotation measure (RM) of an actively repeating source named FRB 20201124A. The detection… ▽ More Fast radio bursts (FRBs) are luminous, dispersed millisecond-duration radio bursts whose origin is poorly known. Recent observations suggest that some FRBs may reside in binary systems, even though conclusive evidence remains elusive. Here we report the detection of a 26.24$\pm$0.02 day periodicity in Faraday rotation measure (RM) of an actively repeating source named FRB 20201124A. The detection was made from 3,106 bursts collected with the Five-hundred-meter Aperture Spherical radio Telescope (FAST) over ~365 days. The RM periodicity is coherently phase-connected across ~14 cycles over a 1-year duration. Our detection of RM periodicity corresponds to a natural logarithmic Bayesian factor of 1,168. The detection significances vary between 5.9-34 σ under different assumptions. Such a periodicity provides evidence for the binary nature of FRB 20201124A, where the periodic RM variations arise from the orbital motion of the FRB source within the magnetoionic environment of the system. Together with previous observations, our result suggests that being in binary systems may be a common feature for actively repeating FRB sources. △ Less

Submitted 13 May, 2025; v1 submitted 9 May, 2025; originally announced May 2025.

Comments: Submitted, comments are welcome

Measurement of separate electron and positron spectra from 10 GeV to 20GeV with the geomagnetic field on DAMPE

Authors: DAMPE Collaboration, F. Alemanno, Q. An, P. Azzarello, F. C. T. Barbato, P. Bernardini, X. J. Bi, H. Boutin, I. Cagnoli, M. S. Cai, E. Casilli, E. Catanzani, J. Chang, D. Y. Chen, J. L. Chen, Z. F. Chen, Z. X. Chen, P. Coppin, M. Y. Cui, T. S. Cui, Y. X. Cui, I. DeMitri, F. dePalma, A. DiGiovanni, T. K. Dong , et al. (127 additional authors not shown)

Abstract: The cosmic-ray (CR) electrons and positrons in space are of great significance for studying the origin and propagation of cosmic-rays. The satellite-borne experiment DArk Matter Particle Explorer (DAMPE) has been used to measure the separate electron and positron spectra, as well as the positron fraction. In this work, the Earth's magnetic field is used to distinguish CR electrons and positrons, a… ▽ More The cosmic-ray (CR) electrons and positrons in space are of great significance for studying the origin and propagation of cosmic-rays. The satellite-borne experiment DArk Matter Particle Explorer (DAMPE) has been used to measure the separate electron and positron spectra, as well as the positron fraction. In this work, the Earth's magnetic field is used to distinguish CR electrons and positrons, as the DAMPE detector does not carry an onboard magnet. The energy range for the measurements is from 10 to 20 GeV, being currently limited at high energy by the zenith pointing orientation of DAMPE. The results are consistent with previous measurements based on the magnetic spectrometer by AMS-02 and PAMELA, while the results of Fermi-LAT seem then to be systematically shifted to larger values. △ Less

Submitted 21 August, 2025; v1 submitted 9 May, 2025; originally announced May 2025.

Comments: Accepted for publication in Chinese Physics C

Deep Neural Networks for Modeling Astrophysical Nuclear Reacting Flows

Authors: Xiaoyu Zhang, Yuxiao Yi, Lile Wang, Zhi-Qin John Xu, Tianhan Zhang, Yao Zhou

Abstract: In astrophysical simulations, nuclear reacting flows pose computational challenges due to the stiffness of reaction networks. We introduce neural network-based surrogate models using the DeePODE framework to enhance simulation efficiency while maintaining accuracy and robustness. Our method replaces conventional stiff ODE solvers with deep learning models trained through evolutionary Monte Carlo s… ▽ More In astrophysical simulations, nuclear reacting flows pose computational challenges due to the stiffness of reaction networks. We introduce neural network-based surrogate models using the DeePODE framework to enhance simulation efficiency while maintaining accuracy and robustness. Our method replaces conventional stiff ODE solvers with deep learning models trained through evolutionary Monte Carlo sampling from zero-dimensional simulation data, ensuring generalization across varied thermonuclear and hydrodynamic conditions. Tested on 3-species and 13-species reaction networks, the models achieve $\lesssim 1\%$ accuracy relative to semi-implicit numerical solutions and deliver a $\sim 2.6\times$ speedup on CPUs. A temperature-thresholded deployment strategy ensures stability in extreme conditions, sustaining neural network utilization above 75\% in multi-dimensional simulations. These data-driven surrogates effectively mitigate stiffness constraints, offering a scalable approach for high-fidelity modeling of astrophysical nuclear reacting flows. △ Less

Submitted 13 October, 2025; v1 submitted 19 April, 2025; originally announced April 2025.

Dust Growth in ALMA Rings: II. Dusty Rossby Wave Instability

Authors: Can Cui, Konstantin Gerbig, Ya-Ping Li, Ziyan Xu, Rixin Li, Cong Yu, Min-Kai Lin, Feng Yuan

Abstract: Annular substructures serve as ideal venues for planetesimal formation. In this series, we investigate the linear stage of dust growth within rings. The first paper examines the global streaming instability, while this study focuses on the dusty Rossby wave instability (DRWI). We perform a linear analysis of the two-fluid equations on a background pressure bump, representing annular substructures.… ▽ More Annular substructures serve as ideal venues for planetesimal formation. In this series, we investigate the linear stage of dust growth within rings. The first paper examines the global streaming instability, while this study focuses on the dusty Rossby wave instability (DRWI). We perform a linear analysis of the two-fluid equations on a background pressure bump, representing annular substructures. The spectral code \textsc{Dedalus} is used to solve the linear eigenvalue problem. We identify two distinct DRWI modes: Type I, which originates from dust-modified gas RWI, and Type II, which results from dust-gas coupling. These modes never coexist for a given azimuthal wavenumber $\ky$, but transition between each other as $\ky$ varies. Type I modes are driven by the advection of background vorticity, whereas Type II modes involve two primary waves: Rossby waves, driven by advection, and thin waves, driven by dust-gas drag. Finally, we assess the relevance of DRWI in ALMA rings using DSHARP sources. Our findings suggest that Type I modes could explain the absence of azimuthal asymmetries in many ALMA disks, whereas Type II modes are entirely absent in all eight observed rings, implying that unresolved narrow rings or alternative mechanisms may play a role in dust growth within annular substructures. △ Less

Submitted 30 April, 2025; v1 submitted 7 April, 2025; originally announced April 2025.

Comments: 24 pages, 15 figures, accepted to ApJ, DOI: 10.3847/1538-4357/add146

The flat tail in the burst energy distribution of FRB 20240114A

Authors: Yu-Xiang Huang, Jun-Shuo Zhang, Heng Xu, Long-Fei Hao, Ke-Jia Lee, Yong-Kun Zhang, Tian-Cong Wang, Shuo Cao, De-Jiang Zhou, Jiang-Wei Xu, Zhi-Xuan Li, Yong-Hua Xu, Bo-Jun Wang, Jin-Chen Jiang, Yan-Jun Guo, Zi-Han Xue, Fa-Xin Shen, Min Wang, Yun-Peng Men, Wen Chen, Qin Wu, Fayin Wang

Abstract: Fast Radio Bursts (FRBs) are enigmatic millisecond-duration radio transients of extra-galactic origin, whose underlying mechanisms and progenitors remain poorly understood. FRBs are broadly classified into two categories: repeating FRBs, which emit multiple bursts over time, and one-off FRBs, which are detected as single events. A central question in FRB research is whether these two classes share… ▽ More Fast Radio Bursts (FRBs) are enigmatic millisecond-duration radio transients of extra-galactic origin, whose underlying mechanisms and progenitors remain poorly understood. FRBs are broadly classified into two categories: repeating FRBs, which emit multiple bursts over time, and one-off FRBs, which are detected as single events. A central question in FRB research is whether these two classes share a common origin. In this study, we present observations of FRB 20240114A, a repeating FRB that entered a hyperactive phase in January 2024. We conducted a 318-hour monitoring campaign using the Kunming 40-Meter Radio Telescope (KM40M) in the S-band (2.187-2.311 GHz), during which we detected eight radio bursts. We analyzed their properties, including dispersion measure (DM), bandwidth, pulse width, flux, fluence, and energy. Additionally, we searched for counterparts in overlapping data from the Five-hundred-meter Aperture Spherical Telescope (FAST) in the L-band (1.0-1.5 GHz). While no bursts were temporally aligned between the two telescopes, we identified one FAST burst that arrived approximately 6 ms after one of the KM40M bursts. The absence of FAST counterparts for the KM40M bursts suggests that individual bursts from FRB 20240114A are likely narrow-band, with fractional bandwidths less than 10%. By comparing the cumulative event rates from KM40M and FAST observations, we found that the two measurements are compatible, indicating a possible flattening of the event rate at higher energies. This feature aligns with observations of one-off FRBs, supporting the hypothesis that repeating and one-off FRBs may share a common origin. △ Less

Submitted 4 April, 2025; originally announced April 2025.

Comments: 14 pages, 5 figures, submitted to RAA, comments are welcome

Spreading and multi-wavelength emissions of an ultra-narrow relativistic jet from GRB 221009A

Authors: Jin-Jun Geng, Ying-Kang Zhang, Hao-Xuan Gao, Fan Xu, Bing Li, Tian-Rui Sun, Ai-Ling Wang, Zhi-Jun Xu, Yuan-Qi Liu, Jun Yang, Chen-Ran Hu, Lauren Rhodes, Liang Li, Yu Wang, Ye Li, Di Xiao, Jia Ren, Bing Zhang, Tao An, Xue-Feng Wu, Yong-Feng Huang, Zi-Gao Dai

Abstract: The long-term evolution of relativistic jets in gamma-ray bursts (GRBs), particularly from days to months post-burst, remains a fundamental puzzle in astrophysics. Here, we report our very long baseline interferometry observation of the brightest GRB 221009A from 5 to 26 days post-burst. Combined with released data, we uncover a remarkable two-stage evolution of the jet lateral size. The jet size… ▽ More The long-term evolution of relativistic jets in gamma-ray bursts (GRBs), particularly from days to months post-burst, remains a fundamental puzzle in astrophysics. Here, we report our very long baseline interferometry observation of the brightest GRB 221009A from 5 to 26 days post-burst. Combined with released data, we uncover a remarkable two-stage evolution of the jet lateral size. The jet size initially grew slowly but later expanded rapidly, challenging conventional scenarios. The slow-evolving stage provides a robust lower limit on the jet opening angle and direct evidence of jet propagation in the uniform interstellar medium at this period. The synergy analysis of the whole jet size evolution and multi-wavelength emissions uncovers that GRB 221009A harbors an ultra-narrow jet (with a half-opening angle $\simeq$ 0.01-0.03~radian) that propagates through a wind-like medium before encountering the interstellar medium, which finally undergoes lateral spreading after significant deceleration. These findings provide crucial new insights into relativistic jet dynamics and establish GRB 221009A as a unique case study for understanding the complex physics of GRB outflows. △ Less

Submitted 22 March, 2025; originally announced March 2025.

Comments: 30 pages, 13 figures, the two first authors contributed equally; comments welcome!

Distinguishing Between Dark Matter-Black Hole Systems and Naked Singularities via Quasi-Periodic Oscillations

Authors: Zheng Ma, Meirong Tang, Zhaoyi Xu

Abstract: Quasi-Periodic Oscillations (QPOs) are an important phenomenon commonly observed in the X-ray radiation of black holes and neutron stars, closely related to the dynamics of accretion disks around compact objects and general relativistic effects. The objective of this study is to use the QPO phenomenon to distinguish between dark matter-black hole systems and naked singularities, as well as to inve… ▽ More Quasi-Periodic Oscillations (QPOs) are an important phenomenon commonly observed in the X-ray radiation of black holes and neutron stars, closely related to the dynamics of accretion disks around compact objects and general relativistic effects. The objective of this study is to use the QPO phenomenon to distinguish between dark matter-black hole systems and naked singularities, as well as to investigate the effects of different dark matter models (Cold Dark Matter, CDM, and Scalar Field Dark Matter, SFDM) on the accretion disk dynamics. By introducing a dark matter correction model within the framework of general relativity, we systematically investigate the differences in dragging effects, characteristic frequency distribution, and the innermost stable circular orbit (ISCO) radius between dark matter-black hole systems and naked singularities, while analyzing the potential coupling between QPO frequencies and dark matter distribution. The main results of this study are as follows: $ν_r$ and $ν_θ$ in dark matter-black hole systems can be identified as HFQPOs, while for lower spins ($a < 0.5$), $ν_\text{nod}$ can be identified as LFQPOs, and for higher spins ($1 > a \geq 0.5$), $ν_\text{nod}$ falls within the HFQPO observation range. Cold Dark Matter (CDM) and Scalar Field Dark Matter (SFDM) modulate the accretion disk dynamics at the order of $10^{-6}$. △ Less

Submitted 15 March, 2025; originally announced March 2025.

Investigation of Inverse Velocity Dispersion in a Solar Energetic Particle Event Observed by Solar Orbiter

Authors: Zheyi Ding, F. Robert Wimmer-Schweingruber, Alexander Kollhoff, Patrick Kühl, Liu Yang, Lars Berger, Athanasios Kouloumvakos, Nicolas Wijsen, Jingnan Guo, Daniel Pacheco, Yuncong Li, Manuela Temmer, Javier Rodriguez-Pacheco, C. Robert Allen, C. George Ho, M. Glenn Mason, Zigong Xu, Sindhuja G

Abstract: Inverse velocity dispersion (IVD) events, characterized by higher-energy particles arriving later than lower-energy particles, challenge the classical understanding of SEP events and are increasingly observed by spacecraft, such as Parker Solar Probe (PSP) and Solar Orbiter (SolO). However, the mechanisms underlying IVD events remain poorly understood. This study aims to investigate the physical p… ▽ More Inverse velocity dispersion (IVD) events, characterized by higher-energy particles arriving later than lower-energy particles, challenge the classical understanding of SEP events and are increasingly observed by spacecraft, such as Parker Solar Probe (PSP) and Solar Orbiter (SolO). However, the mechanisms underlying IVD events remain poorly understood. This study aims to investigate the physical processes responsible for long-duration IVD events by analyzing the SEP event observed by SolO on 2022 June 7. We explore the role of evolving shock connectivity, particle acceleration at interplanetary (IP) shocks, and cross-field transport in shaping the observed particle profiles.We utilize data from Energetic Particle Detector (EPD) suite onboard SolO to analyze the characteristics of the IVD, and model the event using the Heliospheric Energetic Particle Acceleration and Transport (HEPAT) model. The IVD event exhibited a distinct and long-duration IVD signature, across proton energies from 1 to 20 MeV and lasting for approximately 10 hours. Simulations suggest that evolving shock connectivity and the evolution of shock play a primary role in the IVD signature, with SolO transitioning from shock flank to nose over time, resulting in a gradual increase in maximum particle energy along the field line. Furthermore, model results show that limited cross-field diffusion can influence both the nose energy and the duration of the IVD event. This study demonstrates that long-duration IVD events are primarily driven by evolving magnetic connectivity along a non-uniform shock that evolves over time, where the connection moves to more efficient acceleration sites as the shock propagates farther from the Sun. Other mechanisms, such as acceleration time at the shock, may also contribute to the observed IVD features. △ Less

Submitted 16 March, 2025; originally announced March 2025.

Comments: Accepted by A&A. 13 pages, 9 figures

Journal ref: A&A 696, A199 (2025)

A pilot survey on globular clusters with the Wide Field Survey Telescope (WFST)

Authors: Zhen Wan, Lulu Fan, Xuzhi Li, Xu Kong, Tinggui Wang, Qingfeng Zhu, Ji-an Jiang, Minxuan Cai, Zelin Xu, Xianzhong Zheng, Jingquan Cheng, Feng Li, Ming Liang, Hao Liu, Wentao Luo, Jinlong Tang, Hairen Wang, Jian Wang, Yongquan Xue, Dazhi Yao, Hongfei Zhang, Wen Zhao

Abstract: We carry out an imaging survey of six globular clusters (GCs) with a limit magnitude to 22 mag at the 5 sigma level, down to the main sequence stars of the respective cluster, as one of the pilot observing program of the Wide Field Survey Telescope (WFST). This paper present the early results of this survey, where we investigate the tidal characters at the periphery of the clusters NGC 4147, NGC 5… ▽ More We carry out an imaging survey of six globular clusters (GCs) with a limit magnitude to 22 mag at the 5 sigma level, down to the main sequence stars of the respective cluster, as one of the pilot observing program of the Wide Field Survey Telescope (WFST). This paper present the early results of this survey, where we investigate the tidal characters at the periphery of the clusters NGC 4147, NGC 5024, NGC 5053, NGC 5272, NGC 5904 and NGC 6341. We present the estimated number density of cluster candidates and their spatial distribution. We confirm the presence of tidal arms in NGC 4147 and NGC 5904 and identify several intriguing potential tidal structures in NGC 4147, NGC 5024, NGC 5272, corroborated the elliptical morphology of the periphery of NGC 6341. WFST shows its ability to detect faint main-sequence stars of clusters beyond 15 kpc in helio-centric distance. Our findings underscore the WFST's capability for probing faint structural features in GCs, paving the way for future in-depth studies, especially for the search of the large scale tidal streams associated with the clusters with the future wide field survey. △ Less

Submitted 29 April, 2025; v1 submitted 7 March, 2025; originally announced March 2025.

Comments: 13 pages, 8 figures. accepted by MNRAS. Comments are welcome

The Simons Observatory: Science Goals and Forecasts for the Enhanced Large Aperture Telescope

Authors: The Simons Observatory Collaboration, M. Abitbol, I. Abril-Cabezas, S. Adachi, P. Ade, A. E. Adler, P. Agrawal, J. Aguirre, Z. Ahmed, S. Aiola, T. Alford, A. Ali, D. Alonso, M. A. Alvarez, R. An, K. Arnold, P. Ashton, Z. Atkins, J. Austermann, S. Azzoni, C. Baccigalupi, A. Baleato Lizancos, D. Barron, P. Barry, J. Bartlett , et al. (397 additional authors not shown)

Abstract: We describe updated scientific goals for the wide-field, millimeter-wave survey that will be produced by the Simons Observatory (SO). Significant upgrades to the 6-meter SO Large Aperture Telescope (LAT) are expected to be complete by 2028, and will include a doubled mapping speed with 30,000 new detectors and an automated data reduction pipeline. In addition, a new photovoltaic array will supply… ▽ More We describe updated scientific goals for the wide-field, millimeter-wave survey that will be produced by the Simons Observatory (SO). Significant upgrades to the 6-meter SO Large Aperture Telescope (LAT) are expected to be complete by 2028, and will include a doubled mapping speed with 30,000 new detectors and an automated data reduction pipeline. In addition, a new photovoltaic array will supply most of the observatory's power. The LAT survey will cover about 60% of the sky at a regular observing cadence, with five times the angular resolution and ten times the map depth of Planck. The science goals are to: (1) determine the physical conditions in the early universe and constrain the existence of new light particles; (2) measure the integrated distribution of mass, electron pressure, and electron momentum in the late-time universe, and, in combination with optical surveys, determine the neutrino mass and the effects of dark energy via tomographic measurements of the growth of structure at $z < 3$; (3) measure the distribution of electron density and pressure around galaxy groups and clusters, and calibrate the effects of energy input from galaxy formation on the surrounding environment; (4) produce a sample of more than 30,000 galaxy clusters, and more than 100,000 extragalactic millimeter sources, including regularly sampled AGN light-curves, to study these sources and their emission physics; (5) measure the polarized emission from magnetically aligned dust grains in our Galaxy, to study the properties of dust and the role of magnetic fields in star formation; (6) constrain asteroid regoliths, search for Trans-Neptunian Objects, and either detect or eliminate large portions of the phase space in the search for Planet 9; and (7) provide a powerful new window into the transient universe on time scales of minutes to years, concurrent with observations from Rubin of overlapping sky. △ Less

Submitted 7 August, 2025; v1 submitted 1 March, 2025; originally announced March 2025.

Comments: 45 pages, 7 figures; abstract slightly abridged; matches JCAP accepted version. Author contributions to this paper are available at https://simonsobservatory.org/wp-content/uploads/2025/03/Author-contribution-statement-20250228.pdf

The Chinese pulsar timing array data release I. Polarimetry for 56 millisecond pulsars

Authors: Jiangwei Xu, Jinchen Jiang, Heng Xu, Bojun Wang, Zihan Xue, Siyuan Chen, Yanjun Guo, R. Nicolas Caballero, Kejia Lee, Jianping Yuan, Yonghua Xu, Jingbo Wang, Longfei Hao, Zhixuan Li, Yuxiang Huang, Zezhong Xu, Jintao Luo, Jinlin Han, Peng Jiang, Zhiqiang Shen, Min Wang, Na Wang, Renxin Xu, Xiangping Wu, Lei Qian , et al. (5 additional authors not shown)

Abstract: We present polarization pulse profiles for 56 millisecond pulsars (MSPs) monitored by the Chinese Pulsar Timing Array (CPTA) collaboration using the Five-hundred-meter Aperture Spherical radio Telescope (FAST). The observations centered at 1.25 GHz with a raw bandwidth of 500 MHz. Due to the high sensitivity ($\sim$16 K/Jy) of the FAST telescope and our long integration time, the high signal-to-no… ▽ More We present polarization pulse profiles for 56 millisecond pulsars (MSPs) monitored by the Chinese Pulsar Timing Array (CPTA) collaboration using the Five-hundred-meter Aperture Spherical radio Telescope (FAST). The observations centered at 1.25 GHz with a raw bandwidth of 500 MHz. Due to the high sensitivity ($\sim$16 K/Jy) of the FAST telescope and our long integration time, the high signal-to-noise ratio polarization profiles show features hardly detected before. Among 56 pulsars, the polarization profiles of PSRs J0406$+$3039, J1327$+$3423, and J2022$+$2534 were not previously reported. 80\% of MSPs in the sample show weak components below 3\% of peak flux, 25\% of pulsars show interpulse-like structures, and most pulsars show linear polarization position angle jumps. Six pulsars seem to be emitting for full rotation phase, with another thirteen pulsars being good candidates for such a 360$^\circ$ radiator. We find that the distribution of the polarization percentage in our sample is compatible with the normal pulsar distribution. Our detailed evaluation of the MSP polarization properties suggests that the wave propagation effects in the pulsar magnetosphere are important in shaping the MSP polarization pulse profiles. △ Less

Submitted 20 April, 2025; v1 submitted 28 February, 2025; originally announced February 2025.

Comments: 27 pages, 11 figures, 2 tables, accepted by A&A

Journal ref: A&A, 695 (2025) A173

H I absorption line and anomalous dispersion in the radio pulses of PSR B1937+21

Authors: Jinchen Jiang, Shunshun Cao, Kejia Lee, Bojun Wang, Heng Xu, Siyuan Chen, Yanjun Guo, Peng Jiang, Weicong Jing, Jiguang Lu, Jiangwei Xu, Renxin Xu, Zihan Xue

Abstract: We use the Five-hundred-meter Aperture Spherical radio Telescope to observe the bright millisecond pulsar PSR B1937+21 (J1939+2134) and record the data in the band from 1.0 to 1.5 GHz. We measure the neutral hydrogen (HI) emission and absorption lines near 1420 MHz ($λ\simeq 21$ cm). We derive the kinematic distance of the pulsar with the HI observation. By comparing this with the archival absorpt… ▽ More We use the Five-hundred-meter Aperture Spherical radio Telescope to observe the bright millisecond pulsar PSR B1937+21 (J1939+2134) and record the data in the band from 1.0 to 1.5 GHz. We measure the neutral hydrogen (HI) emission and absorption lines near 1420 MHz ($λ\simeq 21$ cm). We derive the kinematic distance of the pulsar with the HI observation. By comparing this with the archival absorption spectra observed decades ago, we notice possible variations in the absorption spectra toward this pulsar, which correspond to a possible tiny-scale atomic structure of a few astronomical units in size. We also verify the apparent faster-than-light anomalous dispersion at the HI absorption line of this pulsar previously reported. △ Less

Submitted 30 July, 2025; v1 submitted 27 February, 2025; originally announced February 2025.

Comments: 12 pages, 5 figures, 2 tables

Journal ref: ApJ 988 (2025) 277

WIMP Dark Matter Search using a 3.1 Tonne-Year Exposure of the XENONnT Experiment

Authors: E. Aprile, J. Aalbers, K. Abe, S. Ahmed Maouloud, L. Althueser, B. Andrieu, E. Angelino, D. Antón Martin, S. R. Armbruster, F. Arneodo, L. Baudis, M. Bazyk, L. Bellagamba, R. Biondi, A. Bismark, K. Boese, A. Brown, G. Bruno, R. Budnik, C. Cai, C. Capelli, J. M. R. Cardoso, A. P. Cimental Chávez, A. P. Colijn, J. Conrad , et al. (153 additional authors not shown)

Abstract: We report on a search for weakly interacting massive particle (WIMP) dark matter (DM) via elastic DM-xenon-nucleus interactions in the XENONnT experiment. We combine datasets from the first and second science campaigns resulting in a total exposure of 3.1 tonne-years. In a blind analysis of nuclear recoil events with energies above $3.8\,\mathrm{keV_{NR}}$, we find no significant excess above back… ▽ More We report on a search for weakly interacting massive particle (WIMP) dark matter (DM) via elastic DM-xenon-nucleus interactions in the XENONnT experiment. We combine datasets from the first and second science campaigns resulting in a total exposure of 3.1 tonne-years. In a blind analysis of nuclear recoil events with energies above $3.8\,\mathrm{keV_{NR}}$, we find no significant excess above background. We set new upper limits on the spin-independent WIMP-nucleon scattering cross section for WIMP masses above $10\,\mathrm{GeV}/c^2$ with a minimum of $1.7\,\times\,10^{-47}\,\mathrm{cm^2}$ at $90\,\%$ confidence level for a WIMP mass of $30\,\mathrm{GeV}/c^2$. We achieve a best median sensitivity of $1.4\,\times\,10^{-47}\,\mathrm{cm^2}$ for a $41\,\mathrm{GeV}/c^2$ WIMP. Compared to the result from the first XENONnT science dataset, we improve our sensitivity by a factor of up to 1.8. △ Less

Submitted 16 December, 2025; v1 submitted 25 February, 2025; originally announced February 2025.

Comments: Limits are included in the submission file

Journal ref: Phys. Rev. Lett. 135, 221003 (2025)

Radial dependence of ion fluences in the 2023 July 17 SEP event from Parker Solar Probe to STEREO and ACE

Authors: G. D. Muro, C. M. S Cohen, Z. Xu, R. A. Leske, E. R. Christian, A. C. Cummings, G. De Nolfo, M. I. Desai, F. Fraschetti, J. Giacalone, A. Labrador, D. J. McComas, J. G. Mitchell, D. G. Mitchell, J. Rankin, N. A. Schwadron, M. Shen, M. E. Wiedenbeck, S. D. Bale, O. Romeo, A. Vourlidas

Abstract: In the latter moments of 17 July 2023, the solar active region 13363, near the southwestern face of the Sun, was undergoing considerable evolution, which resulted in a significant solar energetic particle (SEP) event measured by Parker Solar Probe's Integrated Science Investigation of the Sun (ISOIS) and near-Earth spacecraft. Remote observations from GOES and CHASE captured two M5.0+ solar flares… ▽ More In the latter moments of 17 July 2023, the solar active region 13363, near the southwestern face of the Sun, was undergoing considerable evolution, which resulted in a significant solar energetic particle (SEP) event measured by Parker Solar Probe's Integrated Science Investigation of the Sun (ISOIS) and near-Earth spacecraft. Remote observations from GOES and CHASE captured two M5.0+ solar flares that peaked at 23:34 and 00:06 UT from the source region. In tandem, STEREO COR2 first recorded a small, narrow coronal mass ejection (CME) emerging at 22:54 UT and then saw a major halo CME emerge at 23:43 UT with a bright, rapidly expanding core and CME-driven magnetic shock with an estimated speed of $\sim$1400 $kms^{-1}$. Parker Solar Probe was positioned at 0.65 au, near-perfectly on the nominal Parker spiral magnetic field line which connected Earth and the active region for a 537 $kms^{-1}$ ambient solar wind speed at L1. This fortuitous alignment provided the opportunity to examine how the SEP velocity dispersion, energy spectra, elemental composition, and fluence varied from 0.65 to 1 au along a shared magnetic connection to the Sun. We find a strong radial gradient, which is best characterized for H and He as $r^{-4.0}$ and most surprisingly is stronger for O and Fe which is better described by $r^{-5.7}$. △ Less

Submitted 24 February, 2025; originally announced February 2025.

Comments: The Astrophysical Journal: 10 pages, 13 figures

High-redshift quasars at $z \geq 3$ -- III. Parsec-scale jet properties from VLBI observations

Authors: Shaoguang Guo, Tao An, Yuanqi Liu, Chuanzeng Liu, Zhijun Xu, Yulia Sotnikova, Timur Mufakharov, Ailing Wang

Abstract: High redshift active galactic nuclei (AGN) provide key insights into early supermassive black hole growth and cosmic evolution. This study investigates the parsec-scale properties of 86 radio-loud quasars at z $\geq$ 3 using very long baseline interferometry (VLBI) observations. Our results show predominantly compact core and core-jet morphologies, with 35\% unresolved cores, 59\% core-jet structu… ▽ More High redshift active galactic nuclei (AGN) provide key insights into early supermassive black hole growth and cosmic evolution. This study investigates the parsec-scale properties of 86 radio-loud quasars at z $\geq$ 3 using very long baseline interferometry (VLBI) observations. Our results show predominantly compact core and core-jet morphologies, with 35\% unresolved cores, 59\% core-jet structures, and only 6\% core-double jet morphology. Brightness temperatures are generally lower than expected for highly radiative sources. The jet proper motions are surprisingly slow compared to lower-redshift samples. We observe a high fraction of young and/or confined peak-spectrum sources, providing insights into early AGN evolution in dense environments during early cosmic epochs. The observed trends may reflect genuine evolutionary changes in AGN structure over cosmic time, or selection effects favoring more compact sources at higher redshifts. These results stress the complexity of high-redshift radio-loud AGN populations and emphasize the need for multi-wavelength, high-resolution observations to fully characterize their properties and evolution through cosmic history. △ Less

Submitted 21 February, 2025; originally announced February 2025.

Comments: 23 pages, 9 figures

Development and Performance Validation of a Versatile VLBI Digital Backend Using the ROACH2 Platform

Authors: Jiyun Li, Renjie Zhu, Shaoguang Guo, Ping Rui, Zhijun Xu

Abstract: Customized digital backends for Very Long Baseline Interferometry (VLBI) are critical components for radio astronomy observatories. There are several serialized products such as the Digital Baseband Converter (DBBC), Reconfigurable Open Architecture Computing Hardware (ROACH) Digital BackEnd (RDBE), and Chinese Data Acquisition System (CDAS). However, the reliance on high-speed analog-to-digital c… ▽ More Customized digital backends for Very Long Baseline Interferometry (VLBI) are critical components for radio astronomy observatories. There are several serialized products such as the Digital Baseband Converter (DBBC), Reconfigurable Open Architecture Computing Hardware (ROACH) Digital BackEnd (RDBE), and Chinese Data Acquisition System (CDAS). However, the reliance on high-speed analog-to-digital converters (ADC) and Field Programmable Gate Arrays (FPGAs) often necessitates dedicated hardware platforms with long development cycles and prohibitive cost, limiting scalability and adaptability to evolving observational needs. To address these challenges, we propose a design leveraging the versatile and cost-effective ROACH2 hardware platform, developed by CASPER (Collaboration for Astronomy Signal Processing and Electronics Research). ROACH2's mature technology and streamlined firmware development capabilities significantly reduce the hardware platform's development cycle and cost, making it ideal for modern astronomical applications. This VLBI digital backend, based on the ROACH2 platform, incorporates key technologies such as Polyphase Filter Banks (PFB) algorithm implementation, digital complex-to-real baseband signal conversion, Mark5B data formatter design and two-bit optimal threshold quantization. These features ensure compatibility with existing systems while providing enhanced performance. The backend's performance was validated through multi-station VLBI experiments, demonstrating its ability to achieve good correlation fringes compared to the customized CDAS2-D system. Furthermore, this platform offers flexibility for rapid deployment of additional digital backends, such as those for spectral line observations, showcasing its potential for broader astronomical applications. △ Less

Submitted 21 February, 2025; originally announced February 2025.

Comments: 12 pages, 8 figures

Progress of the TianQin project

Authors: Jun Luo, Shaojun Bai, Yan-Zheng Bai, Lin Cai, Hao Dang, Qijia Dong, Hui-Zong Duan, Yuanbo Du, Lei Fan, Xinju Fu, Yong Gao, Xingyu Gou, Changlei Guo, Wei Hong, Bin Hu, Heran Hu, Ming Hu, Yi-Ming Hu, Fa Peng Huang, Defeng Gu, Xin Ji, Yuan-Ze Jiang, En-Kun Li, Hongyin Li, Ming Li , et al. (76 additional authors not shown)

Abstract: TianQin is a future space-based gravitational wave observatory targeting the frequency window of $10^{-4}$ Hz $\sim 1$ Hz. A large variety of gravitational wave sources are expected in this frequency band, including the merger of massive black hole binaries, the inspiral of extreme/intermediate mass ratio systems, stellar-mass black hole binaries, Galactic compact binaries, and so on. TianQin will… ▽ More TianQin is a future space-based gravitational wave observatory targeting the frequency window of $10^{-4}$ Hz $\sim 1$ Hz. A large variety of gravitational wave sources are expected in this frequency band, including the merger of massive black hole binaries, the inspiral of extreme/intermediate mass ratio systems, stellar-mass black hole binaries, Galactic compact binaries, and so on. TianQin will consist of three Earth orbiting satellites on nearly identical orbits with orbital radii of about $10^5$ km. The satellites will form a normal triangle constellation whose plane is nearly perpendicular to the ecliptic plane. The TianQin project has been progressing smoothly following the ``0123" technology roadmap. In step ``0", the TianQin laser ranging station has been constructed and it has successfully ranged to all the five retro-reflectors on the Moon. In step ``1", the drag-free control technology has been tested and demonstrated using the TianQin-1 satellite. In step ``2", the inter-satellite laser interferometry technology will be tested using the pair of TianQin-2 satellites. The TianQin-2 mission has been officially approved and the satellites will be launched around 2026. In step ``3", i.e., the TianQin-3 mission, three identical satellites will be launched around 2035 to form the space-based gravitational wave detector, TianQin, and to start gravitational wave detection in space. △ Less

Submitted 16 February, 2025; originally announced February 2025.

Comments: 45 pages, 3 figures

Chinese Pulsar Timing Array upper limits on microhertz gravitational waves from supermassive black-hole binaries using PSR J1713+0747 FAST data

Authors: R. Nicolas Caballero, Heng Xu, Kejia Lee, Siyuan Chen, Yanjun Guo, Jinchen Jiang, Bojun Wan, Jiangwei Xu, Zihan Xue

Abstract: We derive the gravitational-wave (GW) strain upper limits from resolvable supermassive black-hole binaries using the data from the Five-hundred-meter Aperture Spherical radio Telescope (FAST), in the context of the Chinese Pulsar Timing Array project. We focus on circular orbits in the $μ$Hz GW frequency band between $10^{-7}$ and $3\times10^{-6}$ Hz. This frequency band is higher than the traditi… ▽ More We derive the gravitational-wave (GW) strain upper limits from resolvable supermassive black-hole binaries using the data from the Five-hundred-meter Aperture Spherical radio Telescope (FAST), in the context of the Chinese Pulsar Timing Array project. We focus on circular orbits in the $μ$Hz GW frequency band between $10^{-7}$ and $3\times10^{-6}$ Hz. This frequency band is higher than the traditional pulsar timing array band and is less explored. We used the data of the millisecond pulsar PSR J1713+5307 observed between August 2019 and April 2021. A dense observation campaign was carried out in September 2020 to allow for the $μ$Hz band coverage. Our sky-average continuous source upper limit at the 95% confidence level at 1$μ$Hz is 1.26$\times10^{-12}$, while the same limit in the direction of the pulsar is 4.77$\times10^{-13}$. △ Less

Submitted 13 February, 2025; originally announced February 2025.

Comments: Accepted by Research in Astronomy and Astrophysics (RAA)

Simultaneous existence of the ocsillations, counterstreaming flows and mass injections in solar quiescent prominences

Authors: X. L. Yan, Z. K. Xue, J. C. Wang, P. F. Chen, K. F. Ji, C. Xia, L. H. Yang, D. F. Kong, Z. Xu, Y. A. Zhou, Q. L. Li

Abstract: Solar prominences are very spectacular structures embedded in the tenuous and hot solar corona. The counterstreaming flows, a common feature in solar quiescent prominences, have been discovered for more than twenty years. However, the mechanism driving the counterstreaming flows is still elusive. To unveil the nature of this phenomenon, we analyzed the data of a quiescent prominence observed by th… ▽ More Solar prominences are very spectacular structures embedded in the tenuous and hot solar corona. The counterstreaming flows, a common feature in solar quiescent prominences, have been discovered for more than twenty years. However, the mechanism driving the counterstreaming flows is still elusive. To unveil the nature of this phenomenon, we analyzed the data of a quiescent prominence observed by the New Vacuum Solar Telescope (NVST), the Interface Region Imaging Spectrograph (IRIS), and the Solar Dynamical Observatory (SDO). It is found that there is a distinct longitudinal oscillation of prominence plasma along the higher part of the prominence spine in H$α$ observations. The oscillation period is approximately 83 minutes and the amplitude is about 32 Mm. The counterstreaming flows are dominant in the middle part of the prominence spine. The velocities of the counterstreaming flows range from about 4 km s$^{-1}$ to 11 km s$^{-1}$. Moreover, the intermittent mass flows with the upward plumes from the top of the bubbles and tornado-like barbs are observed to be injected into the lower part of the prominence spine from the lower atmosphere. The velocities of these injected mass flows range from about 3 km s$^{-1}$ to 30 km s$^{-1}$. Some injected mass flows exhibit redshifted Doppler signals, while others exhibit blueshifted signals. Based on these high resolution observations, it is found that different parts of the prominence spine exhibit the different dynamic characteristics. These results further advance the understanding of the ubiquitous counterstreaming flows in solar quiescent prominences. △ Less

Submitted 6 February, 2025; originally announced February 2025.

Comments: 14 pages, 7 figures, accepted for publication in ApJ

A Heliocentric-orbiting Objects Processing System (HOPS) for the Wide Field Survey Telescope: Architecture, Processing Workflow, and Preliminary Results

Authors: Shao-Han Wang, Bing-Xue Fu, Jun-Qiang Lu, LuLu Fan, Min-Xuan Cai, Ze-Lin Xu, Xu Kong, Haibin Zhao, Bin Li, Ya-Ting Liu, Qing-feng Zhu, Xu Zhou, Zhen Wan, Jingquan Cheng, Ji-an Jiang, Feng Li, Ming Liang, Hao Liu, Wentao Luo, Zhen Lou, Hairen Wang, Jian Wang, Tinggui Wang, Yongquan Xue, Hongfei Zhang , et al. (1 additional authors not shown)

Abstract: Wide-field surveys have markedly enhanced the discovery and study of solar system objects (SSOs). The 2.5-meter Wide Field Survey Telescope (WFST) represents the foremost facility dedicated to optical time-domain surveys in the northern hemisphere. To fully exploit WFST's capabilities for SSO detection, we have developed a heliocentric-orbiting objects processing system (HOPS) tailored for identif… ▽ More Wide-field surveys have markedly enhanced the discovery and study of solar system objects (SSOs). The 2.5-meter Wide Field Survey Telescope (WFST) represents the foremost facility dedicated to optical time-domain surveys in the northern hemisphere. To fully exploit WFST's capabilities for SSO detection, we have developed a heliocentric-orbiting objects processing system (HOPS) tailored for identifying these objects. This system integrates HelioLinC3D, an algorithm well suited for the WFST survey cadence, characterized by revisiting the same sky field twice on the majority of nights. In this paper, we outline the architecture and processing flow of our SSO processing system. The application of the system to the WFST pilot survey data collected between March and May 2024 demonstrates exceptional performance in terms of both temporal efficiency and completeness. A total of 658,489 observations encompassing 38,520 known asteroids have been documented, and 241 newly discovered asteroids have been assigned provisional designations. In particular, 27% of these new discoveries were achieved using merely two observations per night on three nights. The preliminary results not only illuminate the effectiveness of integrating HelioLinC3D within the SSO processing system, but also emphasize the considerable potential contributions of WFST to the field of solar system science. △ Less

Submitted 29 January, 2025; originally announced January 2025.

Comments: 23 pages, 6 figures, submitted to AAS journal

The 2.5-meter Wide Field Survey Telescope Real-time Data Processing Pipeline I: From raw data to alert distribution

Authors: Minxuan Cai, Zelin Xu, Lulu Fan, Zhen Wan, Xu Kong, Weida Hu, Ji-an Jiang, Lei Hu, Qing-feng Zhu, Guoliang Li, Jie Lin, Min Fang, Yongquan Xue, Xianzhong Zhen, Tinggui Wang

Abstract: The Wide Field Survey Telescope (WFST) is a dedicated photometric surveying facility built jointly by the University of Science and Technology of China (USTC) and the Purple Mountain Observatory (PMO). Since many of its scientific objectives rely on near-real-time data for effective analysis, prompt processing of WFST images is of great significance. To meet this need, we adapted the Rubin Observa… ▽ More The Wide Field Survey Telescope (WFST) is a dedicated photometric surveying facility built jointly by the University of Science and Technology of China (USTC) and the Purple Mountain Observatory (PMO). Since many of its scientific objectives rely on near-real-time data for effective analysis, prompt processing of WFST images is of great significance. To meet this need, we adapted the Rubin Observatory Legacy Survey of Space and Time (LSST) science pipelines to handle the data collected by WFST. This paper presents the complete data processing workflow, from ingestion of raw images to the distribution of alerts, and details the primary data products generated by our pipeline. Researchers using data processed by this pipeline can refer to this document to fully understand the data processing procedures. △ Less

Submitted 24 January, 2025; originally announced January 2025.

Comments: 20 pages, 2 figures

Comparing Methods for Calculating Solar Energetic Particle Intensities: Re-binning versus Spectral Binning

Authors: M. E. Cuesta, L. Y. Khoo, G. Livadiotis, M. M. Shen, J. R. Szalay, D. J. McComas, J. S. Rankin, R. Bandyopadhyay, H. A. Farooki, J. T. Niehof, C. M. S. Cohen, R. A. Leske, Z. Xu, E. R. Christian, M. I. Desai, M. A. Dayeh

Abstract: Solar energetic particle (SEP) events have been observed for decades in the interplanetary medium by spacecraft measuring the intensity of energetic ions and electrons. These intensities provide valuable information about particle acceleration, the effects of bulk plasma dynamics on particle transport, and the anisotropy of particle distributions. Since measured intensities are typically reported… ▽ More Solar energetic particle (SEP) events have been observed for decades in the interplanetary medium by spacecraft measuring the intensity of energetic ions and electrons. These intensities provide valuable information about particle acceleration, the effects of bulk plasma dynamics on particle transport, and the anisotropy of particle distributions. Since measured intensities are typically reported in narrow energy bins, it is common to re-bin intensities over a wider energy range to improve counting statistics. We investigate two methods for calculating intensities across multiple energy bins: a) \textit{re-binned intensity} (\(\overline{j}_{\rm linlin}\)), which is calculated by integrating the intensity over energy space and corresponds to the intensity at an effective energy that depends on the time-varying spectral index, and b) \textit{spectral binned intensity} (\(\overline{j}_{\rm loglog}\)), calculated by integrating the log-intensity in log-energy space, yielding the intensity at the log-centered energy that is independent of the spectral index and remains constant over time. We compare these methods using Parker Solar Probe (PSP) IS\(\odot\)IS measurements of energetic protons, and we prescribe criteria for selecting the appropriate method for different scenarios. Our results show that the re-binned intensity is consistently larger (up to a factor of 5) than the spectral binned intensity for two SEP events observed by PSP, although the time series of the two methods are strongly correlated. Overall, both measures are important for SEP spectral analysis, and the selection of the appropriate measure depends on whether a physical (spectral binned intensity) or a statistical (re-binned intensity) representation is needed for a given analysis. △ Less

Submitted 24 January, 2025; originally announced January 2025.

Comments: 17 pages, 9 Figures, Accepted for Publication in ApJS

A Measurement of the Largest-Scale CMB E-mode Polarization with CLASS

Authors: Yunyang Li, Joseph Eimer, John Appel, Charles Bennett, Michael Brewer, Sarah Marie Bruno, Ricardo Bustos, Carol Chan, David Chuss, Joseph Cleary, Sumit Dahal, Rahul Datta, Jullianna Denes Couto, Kevin Denis, Rolando Dunner, Thomas Essinger-Hileman, Kathleen Harrington, Kyle Helson, Johannes Hubmayr, Jeffrey Iuliano, John Karakla, Tobias Marriage, Nathan Miller, Carolina Morales Perez, Lucas Parker , et al. (12 additional authors not shown)

Abstract: We present measurements of large-scale cosmic microwave background (CMB) E-mode polarization from the Cosmology Large Angular Scale Surveyor (CLASS) 90 GHz data. Using 115 det-yr of observations collected through 2024 with a variable-delay polarization modulator, we achieved a polarization sensitivity of $78\,\mathrm{μK\,arcmin}$, comparable to Planck at similar frequencies (100 and 143 GHz). The… ▽ More We present measurements of large-scale cosmic microwave background (CMB) E-mode polarization from the Cosmology Large Angular Scale Surveyor (CLASS) 90 GHz data. Using 115 det-yr of observations collected through 2024 with a variable-delay polarization modulator, we achieved a polarization sensitivity of $78\,\mathrm{μK\,arcmin}$, comparable to Planck at similar frequencies (100 and 143 GHz). The analysis demonstrates effective mitigation of systematic errors and addresses challenges to large-angular-scale power recovery posed by time-domain filtering in maximum-likelihood map-making. A novel implementation of the pixel-space transfer matrix is introduced, which enables efficient filtering simulations and bias correction in the power spectrum using the quadratic cross-spectrum estimator. Overall, we achieved an unbiased time-domain filtering correction to recover the largest angular scale polarization, with the only power deficit, arising from map-making non-linearity, being characterized as less than $3\%$. Through cross-correlation with Planck, we detected the cosmic reionization at $99.4\%$ significance and measured the reionization optical depth $τ=0.053^{+0.018}_{-0.019}$, marking the first ground-based attempt at such a measurement. At intermediate angular scales ($\ell>30$), our results, both independently and in cross-correlation with Planck, remain fully consistent with Planck's measurements. △ Less

Submitted 5 June, 2025; v1 submitted 21 January, 2025; originally announced January 2025.

Comments: 24 pages, 21 figures, 1 table; accepted by ApJ