Showing 1–49 of 49 results for author: Sun, T

Conditional variational autoencoders for cosmological model discrimination and anomaly detection in cosmic microwave background power spectra

Authors: Tian-Yang Sun, Tian-Nuo Li, He Wang, Jing-Fei Zhang, Xin Zhang

Abstract: The cosmic microwave background power spectra are a primary window into the early universe. However, achieving interpretable, likelihood-compatible compression and fast inference under weak model assumptions remains challenging. We propose a parameter-conditioned variational autoencoder (CVAE) that aligns a data-driven latent representation with cosmological parameters while remaining compatible w… ▽ More The cosmic microwave background power spectra are a primary window into the early universe. However, achieving interpretable, likelihood-compatible compression and fast inference under weak model assumptions remains challenging. We propose a parameter-conditioned variational autoencoder (CVAE) that aligns a data-driven latent representation with cosmological parameters while remaining compatible with standard likelihood analyses. The model achieves high-fidelity compression of the $D_\ell^{TT}$, $D_\ell^{EE}$, and $D_\ell^{TE}$ spectra into just 5 latent dimensions, with reconstruction accuracy exceeding $99.9\%$ within Planck uncertainties. It reliably reconstructs spectra for beyond-$Λ$CDM scenarios, even under parameter extrapolation, and enables rapid inference, reducing the computation time from $\sim$40 hours to $\sim$2 minutes while maintaining posterior consistency. The learned latent space demonstrates a physically meaningful structure, capturing a distributed representation that mirrors known cosmological parameters and their degeneracies. Moreover, it supports highly effective unsupervised discrimination among cosmological models, achieving performance competitive with supervised approaches. Overall, this physics-informed CVAE enables anomaly detection beyond $Λ$CDM and points to physically meaningful directions for refinement. △ Less

Submitted 30 October, 2025; originally announced October 2025.

Comments: 19 pages, 13 figures

Insights into Planet Formation from the Ages, Masses, and Elemental Abundances of Host Stars

Authors: Xunzhou Chen, Tiancheng Sun, Lifei Ye

Abstract: How planetary systems form and evolve is a key question in astronomy. Revealing how host star properties, such as elemental abundances, age, and mass, differ from those of non-host stars, and how they correlate with planetary characteristics such as radius, provides new insights into the formation and evolutionary pathways of planetary systems. We determine precise ages for 18890 dwarfs and subgia… ▽ More How planetary systems form and evolve is a key question in astronomy. Revealing how host star properties, such as elemental abundances, age, and mass, differ from those of non-host stars, and how they correlate with planetary characteristics such as radius, provides new insights into the formation and evolutionary pathways of planetary systems. We determine precise ages for 18890 dwarfs and subgiants from the LAMOST-Kepler-Gaia sample with a mean age uncertainty of about 15 percent (median about 10 percent). Within the framework of Galactic chemical evolution, we find that about 86 percent of planet-hosting stars younger than 8 Gyr occupy the upper branch ([Fe/H] > -0.2) of the characteristic V-shaped age-metallicity relation of the Galactic disk. Based on guiding radii (Rg), we further infer that about 19 percent of these young hosts likely originated in the inner disk and subsequently migrated to the solar neighborhood. Among stars older than 10 Gyr, host stars tend to be more metal-rich, with nearly 59 percent having [Fe/H] > -0.2. This suggests that both young and old planet-hosting stars preferentially form in relatively metal-rich environments. However, for host stars with [Fe/H] < -0.2, we find that their metallicities are on average lower by about 0.16 dex compared to non-host stars of similar age and mass, indicating that [Fe/H] is unlikely to be the dominant factor governing planet formation in metal-poor environments. We also identify a systematic depletion of volatile elements, especially carbon, in planet hosts. Moreover, host star [Fe/H] exhibits a weak correlation with planet radius, while [alpha/Fe] primarily support the formation of small planets. △ Less

Submitted 10 November, 2025; v1 submitted 11 October, 2025; originally announced October 2025.

Comments: 16 pages, 9 figures. Accepted for publication in ApJ

Multiwavelength Observations of the Apparently Non-repeating FRB 20250316A

Authors: Ye Li, Hui Sun, Lei Qian, Dong-Yue Li, Yan-Long Hua, Li-Ping Xin, Cheng-Kui Li, Yi-Han Wang, Jia-Rui Niu, Tian-Rui Sun, Zhu-Heng Yao, Jin-Jun Geng, Chi-Chuan Jin, Nanda Rea, Yuan Liu, Zhi-Chen Pan, Tao An, Vadim Burwitz, Zhi-Ming Cai, Jin-Huang Cao, Yong Chen, Hua-Qing Cheng, Wei-Wei Cui, Hua Feng, Peter Friedrich , et al. (50 additional authors not shown)

Abstract: The physical origin of fast radio bursts (FRBs) remains uncertain. Although multiwavelength observations have been widely conducted, only Galactic FRB~20200428D is associated with an X-ray burst from the magnetar SGR J1935+2154. Here, we present multiwavelength follow-up observations of the nearby bright FRB~20250316A, including the Five-hundred-meter Aperture Spherical radio Telescope (FAST), Ein… ▽ More The physical origin of fast radio bursts (FRBs) remains uncertain. Although multiwavelength observations have been widely conducted, only Galactic FRB~20200428D is associated with an X-ray burst from the magnetar SGR J1935+2154. Here, we present multiwavelength follow-up observations of the nearby bright FRB~20250316A, including the Five-hundred-meter Aperture Spherical radio Telescope (FAST), Einstein Probe (EP) X-ray mission, Chandra X-ray Observatory, Wide Field Survey Telescope (WFST) and Space Variable Object Monitor/Visible Telescope (SVOM/VT). The 13.08-hour FAST follow-up campaign without pulse detection requires an energy distribution flatter than those of well-known repeating FRBs, suggesting that this burst is likely a one-off event. A prompt EP follow-up and multi-epoch observational campaign totaling $>$ 100 ks led to the detection of an X-ray source within the angular resolution of its Follow-up X-ray Telescope (FXT, $10^{\prime\prime}$). A subsequent Chandra observation revealed this source to be offset by $7^{\prime\prime}$ from the FRB position, and established a 0.5-10 keV flux upper limit of $7.6\times 10^{-15}$ $\rm erg\,cm^{-2}\,s^{-1}$ at the FRB position, corresponding to $\sim 10^{39}$ $\rm erg\,s^{-1}$ at the 40 Mpc distance of the host galaxy NGC~4141. These results set one of the most stringent limits on X-ray emission from a non-repeating FRB, disfavoring ultra-luminous X-ray sources (ULXs) as counterparts of apparently one-off FRBs and offering critical insights into afterglow models. Our study suggests that an arcsecond localization of both the FRB and its potential X-ray counterpart is essential for exploring the X-ray counterpart of an FRB. △ Less

Submitted 18 November, 2025; v1 submitted 19 August, 2025; originally announced August 2025.

Comments: Accepted for publication in The Astrophysical Journal

Gravitational wave standard sirens: A brief review of cosmological parameter estimation

Authors: Shang-Jie Jin, Ji-Yu Song, Tian-Yang Sun, Si-Ren Xiao, He Wang, Ling-Feng Wang, Jing-Fei Zhang, Xin Zhang

Abstract: Gravitational wave (GW) observations are expected to serve as a powerful and independent probe of the expansion history of the universe. By providing direct and calibration-free measurements of luminosity distances through waveform analysis, GWs provide a fundamentally different and potentially more robust approach to measuring cosmic-scale distances compared to traditional electromagnetic observa… ▽ More Gravitational wave (GW) observations are expected to serve as a powerful and independent probe of the expansion history of the universe. By providing direct and calibration-free measurements of luminosity distances through waveform analysis, GWs provide a fundamentally different and potentially more robust approach to measuring cosmic-scale distances compared to traditional electromagnetic observations, which is known as the standard siren method. In this review, we present an overview of recent developments in GW standard siren cosmology, the latest observational results, and prospects for constraining cosmological parameters using future GW detections. We first introduce standard sirens based on how redshift information is obtained and outline the Bayesian framework used in cosmological parameter estimation. We then review the measurements on the Hubble constant from the LIGO-Virgo-KAGRA network and present the potential role of future standard siren observations in cosmological parameter estimations. A central focus of this review is the unique ability of GW observations to break cosmological parameter degeneracies inherent in the EM observations. Since the cosmological parameter degeneracy directions of GW and EM observations are quite different (roughly orthogonal in some cases), their combination can significantly improve constraints on cosmological parameters. This complementarity is expected to become one of the most critical advantages for GW standard siren cosmology. Looking forward, we highlight the importance of combining GW standard sirens with other emerging late-universe cosmological probes such as fast radio bursts, 21 cm intensity mapping, and strong gravitational lensing to forge a precise cosmological probe for exploring the late universe. Finally, we introduce the challenges and the role of machine learning in future standard siren analysis. △ Less

Submitted 17 July, 2025; originally announced July 2025.

Comments: 36 pages, 20 figures

A Glimpse of Satellite Galaxies in the Milky Way with the 2.5-meter Wide Field Survey Telescope (WFST): Bootes III and Draco

Authors: Chao Yang, Zhizheng Pan, Min Fang, Xian Zhong Zheng, Binyang Liu, Guoliang Li, Tian-Rui Sun, Ji-An Jiang, Miaomiao Zhang, Zhen Wan, Shuang Liu, Han Qu, Ji Yang, Xu Kong, Wenhao Liu, Yiping Shu, Jiang Chang, Tinggui Wang, Lulu Fan, Yongquan Xue, Wentao Luo, Hongxin Zhang, Zheng Lou, Haibin Zhao, Bin Li , et al. (12 additional authors not shown)

Abstract: We carry out deep imaging of the Milky Way satellite galaxies, Bootes III and Draco, with WFST as one pilot observing program to demonstrate the capability of WFST. Combining catalogs with PS1 DR2 and Gaia DR3, we derive proper motions for candidate member stars in these two satellite galaxies over a 12-year time baseline, yielding uncertainties of ~1.8 mas/yr at 21 mag and ~3.0 mas/yr at 22 mag i… ▽ More We carry out deep imaging of the Milky Way satellite galaxies, Bootes III and Draco, with WFST as one pilot observing program to demonstrate the capability of WFST. Combining catalogs with PS1 DR2 and Gaia DR3, we derive proper motions for candidate member stars in these two satellite galaxies over a 12-year time baseline, yielding uncertainties of ~1.8 mas/yr at 21 mag and ~3.0 mas/yr at 22 mag in the r band. The proper motions derived from bright and faint stars are consistent, indicating no significant variation in proper motion across stellar luminosity as these galaxies undergo tidal interactions with the MW. Meanwhile, we suggest that Bootes III represents the bound remnant of the progenitor galaxy that gave rise to the Styx stream, as evidenced by its elongated density profile and overdensity in both spatial and kinematic space. This is the first paper to use WFST to measure the proper motions of faint stars in Milky Way satellite galaxies. More detailed analyses will be presented in forthcoming papers from the wide field survey (WFS) program. △ Less

Submitted 26 June, 2025; originally announced June 2025.

Comments: 17 pages, 12 figures, 3 tables. Accepted for publication in ApJ

Parameter inference of microlensed gravitational waves using neural spline flows

Authors: Zheng Qin, Tian-Yang Sun, Bo-Yuan Li, Jing-Fei Zhang, Xiao Guo, Xin Zhang

Abstract: When gravitational waves (GWs) propagate near massive objects, they undergo gravitational lensing that imprints lens model dependent modulations on the waveform. This effect provides a powerful tool for cosmological and astrophysical studies. However, conventional Bayesian parameter inference methods for GWs are computationally expensive, especially for lensed events with additional lens parameter… ▽ More When gravitational waves (GWs) propagate near massive objects, they undergo gravitational lensing that imprints lens model dependent modulations on the waveform. This effect provides a powerful tool for cosmological and astrophysical studies. However, conventional Bayesian parameter inference methods for GWs are computationally expensive, especially for lensed events with additional lens parameters, necessitating more efficient approaches. In this work, we explore the use of neural spline flows (NSFs) for posterior inference of microlensed GWs, and successfully apply NSFs to the inference of 11-dimensional lens parameters. Our results demonstrate that compared with traditional methods like Bilby dynesty that rely on Bayesian inference, the NSF network we built not only achieves inference accuracy comparable to traditional methods for the main parameters, but also can reduce the inference time from approximately 3 days to 0.8 s on average. Additionally, the network exhibits strong generalization for the spin parameters of GW sources. It is anticipated to become a powerful tool for future low-latency searches for lensed GW signals. △ Less

Submitted 16 July, 2025; v1 submitted 27 May, 2025; originally announced May 2025.

Comments: 11 pages, 6 figures

$f$-mode oscillations of protoneutron stars

Authors: Zi-Yue Zheng, Ting-Ting Sun, Huan Chen, Jin-Biao Wei, Xiao-Ping Zheng, G. F. Burgio, H. -J. Schulze

Abstract: We investigate nonradial $f$-mode oscillations of protoneutron stars in full general relativity, employing equations of state described by the Brueckner-Hartree-Fock theory or the relativistic mean field model, while assuming isentropy and fixed lepton fractions for the internal structure. The validity of various universal relations for cold neutron stars involving $f$-mode characteristics and mac… ▽ More We investigate nonradial $f$-mode oscillations of protoneutron stars in full general relativity, employing equations of state described by the Brueckner-Hartree-Fock theory or the relativistic mean field model, while assuming isentropy and fixed lepton fractions for the internal structure. The validity of various universal relations for cold neutron stars involving $f$-mode characteristics and macroscopic properties of the star is confirmed for those isentropic protoneutron stars. Prospects of observations are also discussed. According to simulation results, we then model details of the thermal and trapping profiles in a PNS with the canonical mass. The corresponding $f$-mode frequencies and gravitational-wave strain amplitudes are presented. The validity of the universal relations during the evolution to the formation of a cold neutron star is confirmed. △ Less

Submitted 2 December, 2025; v1 submitted 15 May, 2025; originally announced May 2025.

Comments: 15 pages, 11 figures

GRB Timing: Decoding the Hidden Slow Jets in GRB 060729

Authors: Jin-Jun Geng, Ding-Fang Hu, Hao-Xuan Gao, Yi-Fang Liang, Yan-Long Hua, Guo-Rui Zhang, Tian-Rui Sun, Bing Li, Yuan-Qi Liu, Fan Xu, Chen Deng, Chen-Ran Hu, Ming Xu, Yong-Feng Huang, Miao-Miao Zhang, Min Fang, Jing-Zhi Yan, Tao An, Xue-Feng Wu

Abstract: Gamma-ray bursts (GRBs) are luminous stellar explosions characterized by the ejection of relativistic jets. This work proposes a novel paradigm to study these GRB jets. By analyzing the timing information of prompt pulses and X-ray flares, in conjunction with the multi-wavelength afterglow observations, we identify three distinct jets in the extraordinary GRB 060729, with initial bulk Lorentz fact… ▽ More Gamma-ray bursts (GRBs) are luminous stellar explosions characterized by the ejection of relativistic jets. This work proposes a novel paradigm to study these GRB jets. By analyzing the timing information of prompt pulses and X-ray flares, in conjunction with the multi-wavelength afterglow observations, we identify three distinct jets in the extraordinary GRB 060729, with initial bulk Lorentz factors ranging from approximately 20 to 80, smaller than typical values of $> 100$. These three jets undergo two successive collisions, producing the observed pair of X-ray flares. Following these interactions, the system evolves into a fast, narrow jet and a slower, hollow jet that continues to propagate in the circumburst medium, evidenced by the notable twin bumps observed in the X-ray and optical afterglow of GRB 060729. Our findings demonstrate that the timing of the early emission enables us to measure the velocities of the GRB jets. The proposed paradigm enhances our understanding of jet dynamics and shock interactions and serves as a powerful tool for probing the physics of the central engine with the expanded sample in the current golden era of GRB research. △ Less

Submitted 23 April, 2025; v1 submitted 22 March, 2025; originally announced March 2025.

Comments: 15 pages, 6 figures, 2 tables, ApJL accepted

Report number: 2025, ApJL, 984, L65

Journal ref: https://iopscience.iop.org/article/10.3847/2041-8213/add00e

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!

An active repeating fast radio burst in a magnetized eruption environment

Authors: Y. Li, S. B. Zhang, Y. P. Yang, C. W. Tsai, X. Yang, C. J. Law, R. Anna-Thomas, X. L. Chen, K. J. Lee, Z. F. Tang, D. Xiao, H. Xu, X. L. Yang, G. Chen, Y. Feng, D. Z. Li, R. Mckinven, J. R. Niu, K. Shin, B. J. Wang, C. F. Zhang, Y. K. Zhang, D. J. Zhou, Y. H. Zhu, Z. G. Dai , et al. (13 additional authors not shown)

Abstract: Fast radio bursts (FRBs) are millisecond-duration radio bursts with unidentified extra-galactic origin. Some FRBs exhibit mild magneto-ionic environmental variations, possibly attributed to plasma turbulence or geometric configuration variation in a binary system. Here we report an abrupt magneto-ionic environment variation of FRB 20220529, a repeating FRB from a disk galaxy at redshift 0.1839. In… ▽ More Fast radio bursts (FRBs) are millisecond-duration radio bursts with unidentified extra-galactic origin. Some FRBs exhibit mild magneto-ionic environmental variations, possibly attributed to plasma turbulence or geometric configuration variation in a binary system. Here we report an abrupt magneto-ionic environment variation of FRB 20220529, a repeating FRB from a disk galaxy at redshift 0.1839. Initially, its Faraday rotation measure (RM) was $21 \pm 96~{\rm rad~m^{-2}}$ over 17 months. In December 2023, it jumped to $1976.9~{\rm rad~m^{-2}}$, exceeding twenty times of the standard deviation of the previous RM variation, and returned to the typical values within two weeks. Such a drastic RM variation suggests a dense magnetized clump moving across the line of sight, possibly due to coronal mass ejection associated with a stellar flare. It indicates that the FRB likely has a companion star that produced the stellar flare. △ Less

Submitted 6 March, 2025; originally announced March 2025.

Comments: 43 pages, 9 figures, under review in Science, the authors' original version

Analytical modeling of the one-dimensional power spectrum of 21-cm forest based on a halo model method

Authors: Yue Shao, Tian-Yang Sun, Meng-Lin Zhao, Xin Zhang

Abstract: The 21-cm forest, composed of spectral absorption features from high-redshift background radio sources, provides a unique probe for studying small-scale structures during the epoch of reionization. It is particularly sensitive to detecting small-scale structures and early heating processes. Despite the rich information contained in the 21-cm forest signal, the complexity of directly modeling the s… ▽ More The 21-cm forest, composed of spectral absorption features from high-redshift background radio sources, provides a unique probe for studying small-scale structures during the epoch of reionization. It is particularly sensitive to detecting small-scale structures and early heating processes. Despite the rich information contained in the 21-cm forest signal, the complexity of directly modeling the signal has led to a lack of effective analytical models. However, the one-dimensional (1D) power spectrum of the 21-cm forest contains valuable information about the matter power spectrum, making analytical modeling feasible. This work employs an analytical modeling approach based on the halo model, which links the distribution of matter to dark matter halos, allowing for effective predictions of cosmic structure formation and its impact on the 21-cm signal. By considering various parameter scenarios within the halo model framework, particularly different dark matter particle masses and varying levels of cosmic heating, we can capture the complexities of small-scale structures and make the 1D power spectrum modeling applicable across a wide range of parameters. This method not only enhances our understanding of the 21-cm forest signal but also provides theoretical support for future observational data. Observing the 21-cm forest with large radio telescopes, such as the Square Kilometre Array, is anticipated to enable simultaneous exploration of dark matter properties and the heating history of the early universe. △ Less

Submitted 10 September, 2025; v1 submitted 25 November, 2024; originally announced November 2024.

Comments: 12 pages, 7 figures

Journal ref: Physical Review D 112, 063513 (2025)

The temporal and spatial variations of lithium abundance in the Galactic disc

Authors: Tiancheng Sun, Shaolan Bi, Xunzhou Chen, Yuxi, Lu, Yuqin Chen, Ming-Yi Ding, Jianrong Shi, Hongliang Yan, Zhishuai Ge

Abstract: This study investigates the temporal and spatial variations in lithium abundance within the Milky Way using a sample of 22,034 main-sequence turn-off (MSTO) stars and subgiants, characterised by precise stellar ages, 3D NLTE (non-local thermodynamic equilibrium) lithium abundances, and birth radii. Our results reveal a complex variation in lithium abundance with stellar age: a gradual increase fro… ▽ More This study investigates the temporal and spatial variations in lithium abundance within the Milky Way using a sample of 22,034 main-sequence turn-off (MSTO) stars and subgiants, characterised by precise stellar ages, 3D NLTE (non-local thermodynamic equilibrium) lithium abundances, and birth radii. Our results reveal a complex variation in lithium abundance with stellar age: a gradual increase from 14 Gyr to 6 Gyr, followed by a decline between 6 Gyr and 4.5 Gyr, and a rapid increase thereafter. We find that young Li-rich stars (ages $<$ 4 Gyr, A(Li) $>$ 2.7 dex) predominantly originate from the outer disc. By binning the sample according to guiding center radius and z$_{\rm max}$, we observe that these young Li-rich stars migrate radially to the local and inner discs. In addition, the stars originating from the inner disc experienced a rapid Li enrichment process between 8 Gyr and 6 Gyr. Our analysis suggests that the age range of Li-dip stars is 4-5 Gyr, encompassing evolution stages from MSTO stars to subgiants. The Galactic radial profile of A(Li) (with respect to birth radius), as a function of age, reveals three distinct periods: 14-6 Gyr ago, 6-4 Gyr ago, and 4-1 Gyr ago. Initially, the lithium abundance gradient is positive, indicating increasing Li abundance with birth radius. During the second period, it transitions to a negative and broken gradient, mainly affected by Li-dip stars. In the final period, the gradient reverts to a positive trend. △ Less

Submitted 19 November, 2024; originally announced November 2024.

Comments: Accepted for publication in MNRAS. 9 pages, 10 figures

Search for exotic gravitational wave signals beyond general relativity using deep learning

Authors: Yu-Xin Wang, Xiaotong Wei, Chun-Yue Li, Tian-Yang Sun, Shang-Jie Jin, He Wang, Jing-Lei Cui, Jing-Fei Zhang, Xin Zhang

Abstract: The direct detection of gravitational waves by LIGO has confirmed general relativity (GR) and sparked rapid growth in gravitational wave (GW) astronomy. However, subtle post-Newtonian (PN) deviations observed during the analysis of high signal-to-noise ratio events from the observational runs suggest that standard waveform templates, which assume strict adherence to GR, might overlook signals from… ▽ More The direct detection of gravitational waves by LIGO has confirmed general relativity (GR) and sparked rapid growth in gravitational wave (GW) astronomy. However, subtle post-Newtonian (PN) deviations observed during the analysis of high signal-to-noise ratio events from the observational runs suggest that standard waveform templates, which assume strict adherence to GR, might overlook signals from alternative theories of gravity. Incorporating these exotic signals into traditional search algorithms is computationally infeasible due to the vast template space required. This paper introduces a proof-of-principle deep learning framework for detecting exotic GW signals, leveraging neural networks trained on GR-based templates. Through their generalization ability, neural networks learn intricate features from the data, enabling the detection of signals that deviate from GR. We present the first study evaluating the capability of deep learning to detect beyond-GR signals, including a variety of PN orders. Our model achieves rapid and accurate identification of exotic GW signals across different luminosity distances, with performance comparable to GR-based detections. In particular, applying the model to the GW150914 event demonstrates excellent performance, highlighting the potential of AI-driven methods for detecting previously overlooked signals beyond GR. This work paves the way for new discoveries in gravitational wave astronomy, enabling the detection of signals that might escape traditional search pipelines. △ Less

Submitted 10 July, 2025; v1 submitted 26 October, 2024; originally announced October 2024.

Comments: 14 pages, 12 figures

Journal ref: Physical Review D 112, 024030 (2025)

GRB 240529A: A Tale of Two Shocks

Authors: Tian-Rui Sun, Jin-Jun Geng, Jing-Zhi Yan, You-Dong Hu, Xue-Feng Wu, Alberto J. Castro-Tirado, Chao Yang, Yi-Ding Ping, Chen-Ran Hu, Fan Xu, Hao-Xuan Gao, Ji-An Jiang, Yan-Tian Zhu, Yongquan Xue, Ignacio Pérez-García, Si-Yu Wu, Emilio Fernández-García, María D. Caballero-García, Rubén Sánchez-Ramírez, Sergiy Guziy, Ignacio Olivares, Carlos Jesus Pérez del Pulgar, A. Castellón, Sebastián Castillo, Ding-Rong Xiong , et al. (44 additional authors not shown)

Abstract: Thanks to the rapidly increasing time-domain facilities, we are entering a golden era of research on gamma-ray bursts (GRBs). In this Letter, we report our observations of GRB 240529A with the Burst Optical Observer and Transient Exploring System, the 1.5-meter telescope at Observatorio Sierra Nevada, the 2.5-meter Wide Field Survey Telescope of China, the Large Binocular Telescope, and the Telesc… ▽ More Thanks to the rapidly increasing time-domain facilities, we are entering a golden era of research on gamma-ray bursts (GRBs). In this Letter, we report our observations of GRB 240529A with the Burst Optical Observer and Transient Exploring System, the 1.5-meter telescope at Observatorio Sierra Nevada, the 2.5-meter Wide Field Survey Telescope of China, the Large Binocular Telescope, and the Telescopio Nazionale Galileo. The prompt emission of GRB 240529A shows two comparable energetic episodes separated by a quiescence time of roughly 400 s. Combining all available data on the GRB Coordinates Network, we reveal the simultaneous apparent X-ray plateau and optical re-brightening around $10^3-10^4$ s after the burst. Rather than the energy injection from the magnetar as widely invoked for similar GRBs, the multi-wavelength emissions could be better explained as two shocks launched from the central engine separately. The optical peak time and our numerical modeling suggest that the initial bulk Lorentz factor of the later shock is roughly 50, which indicates that the later jet should be accretion-driven and have a higher mass loading than a typical one. The quiescence time between the two prompt emission episodes may be caused by the transition between different accretion states of a central magnetar or black hole, or the fall-back accretion process. A sample of similar bursts with multiple emission episodes in the prompt phase and sufficient follow-up could help to probe the underlying physics of GRB central engines. △ Less

Submitted 26 September, 2024; originally announced September 2024.

Comments: Resubmitted to ApJL after addressing the referee's comments; comments are welcome

Deep learning-driven likelihood-free parameter inference for 21-cm forest observations

Authors: Tian-Yang Sun, Yue Shao, Yichao Li, Yidong Xu, He Wang, Xin Zhang

Abstract: The hyperfine structure absorption lines of neutral hydrogen in spectra of high-redshift radio sources, known collectively as the 21-cm forest, have been demonstrated as a sensitive probe to the small-scale structures governed by the dark matter (DM) properties, as well as the thermal history of the intergalactic medium regulated by the first galaxies during the epoch of reionization. By statistic… ▽ More The hyperfine structure absorption lines of neutral hydrogen in spectra of high-redshift radio sources, known collectively as the 21-cm forest, have been demonstrated as a sensitive probe to the small-scale structures governed by the dark matter (DM) properties, as well as the thermal history of the intergalactic medium regulated by the first galaxies during the epoch of reionization. By statistically analyzing these spectral features, the one-dimensional (1D) power spectrum of the 21-cm forest can effectively break the parameter degeneracies and constrain the properties of both DM and the first galaxies. However, conventional parameter inference methods face challenges due to computationally expensive simulations for 21-cm forest and the non-Gaussian signal characteristics. To address these issues, we introduce generative normalizing flows for data augmentation and inference normalizing flows for parameters estimation. This approach efficiently estimates parameters from minimally simulated datasets with non-Gaussian signals. Using simulated data from the upcoming Square Kilometre Array (SKA), we demonstrate the ability of the deep learning-driven likelihood-free approach to generate accurate posterior distributions, providing a robust and efficient tool for probing DM and the cosmic heating history using the 1D power spectrum of 21-cm forest in the era of SKA. This methodology is adaptable for scientific analyses with other unevenly distributed data. △ Less

Submitted 20 May, 2025; v1 submitted 19 July, 2024; originally announced July 2024.

Comments: 70 pages, 18 figures; accepted for publication in Communications Physics

Journal ref: Communications Physics 8 (2025) 1, 220

Robust inference of gravitational wave source parameters in the presence of noise transients using normalizing flows

Authors: Chun-Yu Xiong, Tian-Yang Sun, Jing-Fei Zhang, Xin Zhang

Abstract: Gravitational wave (GW) detection is of paramount importance in fundamental physics and GW astronomy, yet it presents formidable challenges. One significant challenge is the removal of noise transient artifacts known as glitches, which greatly impact the search and identification of GWs. Recent research has achieved remarkable results in data denoising, often using effective modeling methods to re… ▽ More Gravitational wave (GW) detection is of paramount importance in fundamental physics and GW astronomy, yet it presents formidable challenges. One significant challenge is the removal of noise transient artifacts known as glitches, which greatly impact the search and identification of GWs. Recent research has achieved remarkable results in data denoising, often using effective modeling methods to remove glitches. However, for glitches from uncertain or unknown sources, current methods cannot completely eliminate them from the GW signal. In this work, we leverage the inherent robustness of machine learning to obtain reliable posterior parameter distributions directly from GW data contaminated by glitches. Our network model provides reasonable and rapid parameter inference even in the presence of glitches, without needing to remove them. We also investigate various factors affecting the rationality of parameter inference in our normalizing flow network, including glitch and GW parameters. The results demonstrate that the normalizing flow can reasonably infer the source parameters of GWs even with unknown contamination. We find that the nature of the glitch itself is the only factor that can affect the rationality of the inferred results. With improvements to our model, we anticipate accelerating the localization of electromagnetic counterparts and providing priors for more accurate deglitching, thereby speeding up subsequent data processing procedures. △ Less

Submitted 24 November, 2024; v1 submitted 15 May, 2024; originally announced May 2024.

Comments: 14 pages, 11 figures

Journal ref: Physical Review D 111, 024019 (2025)

New constraints on Triton's atmosphere from the 6 October 2022 stellar occultation

Authors: Ye Yuan, Chen Zhang, Fan Li, Jian Chen, Yanning Fu, Chunhai Bai, Xing Gao, Yong Wang, Tuhong Zhong, Yixing Gao, Liang Wang, Donghua Chen, Yixing Zhang, Yang Zhang, Wenpeng Xie, Shupi Zhang, Ding Liu, Jun Cao, Xiangdong Yin, Xiaojun Mo, Jing Liu, Xinru Han, Tong Liu, Yuqiang Chen, Zhendong Gao , et al. (25 additional authors not shown)

Abstract: The atmosphere of Triton was probed directly by observing a ground-based stellar occultation on 6 October 2022. This rare event yielded 23 positive light curves collected from 13 separate observation stations contributing to our campaign. The significance of this event lies in its potential to directly validate the modest pressure fluctuation on Triton, a phenomenon not definitively verified by pr… ▽ More The atmosphere of Triton was probed directly by observing a ground-based stellar occultation on 6 October 2022. This rare event yielded 23 positive light curves collected from 13 separate observation stations contributing to our campaign. The significance of this event lies in its potential to directly validate the modest pressure fluctuation on Triton, a phenomenon not definitively verified by previous observations, including only five stellar occultations, and the Voyager 2 radio occultation in 1989. Using an approach consistent with a comparable study, we precisely determined a surface pressure of $14.07_{-0.13}^{+0.21}~\mathrm{μbar}$ in 2022. This new pressure rules out any significant monotonic variation in pressure between 2017 and 2022 through direct observations, as it is in alignment with the 2017 value. Additionally, both the pressures in 2017 and 2022 align with the 1989 value. This provides further support for the conclusion drawn from the previous volatile transport model simulation, which is consistent with the observed alignment between the pressures in 1989 and 2017; that is to say, the pressure fluctuation is modest. Moreover, this conclusion suggests the existence of a northern polar cap extended down to at least $45^\circ$N$-60^\circ$N and the presence of nitrogen between $30^\circ$S and $0^\circ$. △ Less

Submitted 24 March, 2024; v1 submitted 14 March, 2024; originally announced March 2024.

Comments: Astronomy & Astrophysics, in press. 9 pages, 2 figures, 3 tables

Journal ref: A&A 684, L13 (2024)

Nuclear mass table in deformed relativistic Hartree-Bogoliubov theory in continuum, II: Even-$Z$ nuclei

Authors: DRHBc Mass Table Collaboration, Peng Guo, Xiaojie Cao, Kangmin Chen, Zhihui Chen, Myung-Ki Cheoun, Yong-Beom Choi, Pak Chung Lam, Wenmin Deng, Jianmin Dong, Pengxiang Du, Xiaokai Du, Kangda Duan, Xiaohua Fan, Wei Gao, Lisheng Geng, Eunja Ha, Xiao-Tao He, Jinniu Hu, Jingke Huang, Kun Huang, Yanan Huang, Zidan Huang, Kim Da Hyung, Hoi Yat Chan , et al. (58 additional authors not shown)

Abstract: The mass table in the deformed relativistic Hartree-Bogoliubov theory in continuum (DRHBc) with the PC-PK1 density functional has been established for even-$Z$ nuclei with $8\le Z\le120$, extended from the previous work for even-even nuclei [Zhang $\it{et.~al.}$ (DRHBc Mass Table Collaboration), At. Data Nucl. Data Tables 144, 101488 (2022)]. The calculated binding energies, two-nucleon and one-ne… ▽ More The mass table in the deformed relativistic Hartree-Bogoliubov theory in continuum (DRHBc) with the PC-PK1 density functional has been established for even-$Z$ nuclei with $8\le Z\le120$, extended from the previous work for even-even nuclei [Zhang $\it{et.~al.}$ (DRHBc Mass Table Collaboration), At. Data Nucl. Data Tables 144, 101488 (2022)]. The calculated binding energies, two-nucleon and one-neutron separation energies, root-mean-square (rms) radii of neutron, proton, matter, and charge distributions, quadrupole deformations, and neutron and proton Fermi surfaces are tabulated and compared with available experimental data. A total of 4829 even-$Z$ nuclei are predicted to be bound, with an rms deviation of 1.477 MeV from the 1244 mass data. Good agreement with the available experimental odd-even mass differences, $α$ decay energies, and charge radii is also achieved. The description accuracy for nuclear masses and nucleon separation energies as well as the prediction for drip lines is compared with the results obtained from other relativistic and nonrelativistic density functional. The comparison shows that the DRHBc theory with PC-PK1 provides an excellent microscopic description for the masses of even-$Z$ nuclei. The systematics of the nucleon separation energies, odd-even mass differences, pairing energies, two-nucleon gaps, $α$ decay energies, rms radii, quadrupole deformations, potential energy curves, neutron density distributions, and neutron mean-field potentials are discussed. △ Less

Submitted 10 June, 2024; v1 submitted 5 February, 2024; originally announced February 2024.

Comments: 394 pages, 17 figures, 2 tables, published in Atomic Data and Nuclear Data Tables, data file in the TXT form is available for download under "Ancillary files"

Journal ref: Peng Guo, et. al. (DRHBc Mass Table Collaboration), Atomic Data and Nuclear Data Tables 158 (2024) 101661

Relations of rotation and chromospheric activity to stellar age for FGK dwarfs from Kepler and LAMOST

Authors: Lifei Ye, Shaolan Bi, Jinghua Zhang, Tiancheng Sun, Liu Long, Zhishuai Ge, Tanda Li, Xianfei Zhang, Xunzhou Chen, Yaguang Li, Jianzhao Zhou, Maosheng Xiang

Abstract: The empirical relations between rotation period, chromospheric activity, and age can be used to estimate stellar age. To calibrate these relations, we present a catalog, including the masses and ages of 52,321 FGK dwarfs, 47,489 chromospheric activity index $logR^{+}_{HK}$, 6,077 rotation period $P_{rot}$ and variability amplitude $S_{ph}$, based on data from LAMOST DR7, Kepler and Gaia DR3. We fi… ▽ More The empirical relations between rotation period, chromospheric activity, and age can be used to estimate stellar age. To calibrate these relations, we present a catalog, including the masses and ages of 52,321 FGK dwarfs, 47,489 chromospheric activity index $logR^{+}_{HK}$, 6,077 rotation period $P_{rot}$ and variability amplitude $S_{ph}$, based on data from LAMOST DR7, Kepler and Gaia DR3. We find a pronounced correlation among $P_{rot}$, age, and [Fe/H] throughout the main-sequence phase for F dwarfs. However, the decrease of $logR^{+}_{HK}$ over time is not significant except for those with [Fe/H] $<$ $-$0.1. For G dwarfs, both $P_{rot}$ and $logR^{+}_{HK}$ are reliable age probes in the ranges $\sim$ 2-11 Gyr and $\sim$ 2-13 Gyr, respectively. K dwarfs exhibit a prominent decrease in $logR^{+}_{HK}$ within the age range of $\sim$ 3-13 Gyr when the relation of $P_{rot}-τ$ is invalid. These relations are very important for promptly estimating the age of a vast number of stars, thus serving as a powerful tool in advancing the fields of exoplanet properties, stellar evolution, and Galactic-archaeology. △ Less

Submitted 27 January, 2024; originally announced January 2024.

Detection of Solar-like Oscillations in Sub-giant and Red Giant Stars Using 2-minute Cadence TESS Data

Authors: Jianzhao Zhou, Shaolan Bi, Jie Yu, Yaguang Li, Xianfei Zhang, Tanda Li, Liu Long, Mengjie Li, Tiancheng Sun, Lifei Ye

Abstract: Based on all 2-minute cadence $TESS$ light curves from Sector 1 to 60, we provide a catalog of 8,651 solar-like oscillators, including frequency at maximum power ($ν_{\rm max}$, with its median precision, $σ$=5.39\%), large frequency separation ($Δν$, $σ$=6.22\%), seismically derived masses, radii, and surface gravity. In this sample, we have detected 2,173 new oscillators and added 4,373 new… ▽ More Based on all 2-minute cadence $TESS$ light curves from Sector 1 to 60, we provide a catalog of 8,651 solar-like oscillators, including frequency at maximum power ($ν_{\rm max}$, with its median precision, $σ$=5.39\%), large frequency separation ($Δν$, $σ$=6.22\%), seismically derived masses, radii, and surface gravity. In this sample, we have detected 2,173 new oscillators and added 4,373 new $Δν$ measurements. Our seismic parameters are consistent with those from $Kepler$, $K2$, and previous $TESS$ data. The median fractional residual in $ν_{\rm max}$ is $1.63\%$ with a scatter of $14.75\%$, and in $Δν$ it is $0.11\%$ with a scatter of $10.76\%$. We have detected 476 solar-like oscillators with $ν_{\rm max}$ exceeding the $Nyquist$ frequency of $Kepler$ long-cadence data during the evolutionary phases of sub-giant and the base of the red-giant branch, which provide a valuable resource for understanding angular momentum transport. △ Less

Submitted 20 January, 2024; originally announced January 2024.

Efficient parameter inference for gravitational wave signals in the presence of transient noises using temporal and time-spectral fusion normalizing flow

Authors: Tian-Yang Sun, Chun-Yu Xiong, Shang-Jie Jin, Yu-Xin Wang, Jing-Fei Zhang, Xin Zhang

Abstract: Glitches represent a category of non-Gaussian and transient noise that frequently intersects with gravitational wave (GW) signals, exerting a notable impact on the processing of GW data. The inference of GW parameters, crucial for GW astronomy research, is particularly susceptible to such interference. In this study, we pioneer the utilization of temporal and time-spectral fusion normalizing flow… ▽ More Glitches represent a category of non-Gaussian and transient noise that frequently intersects with gravitational wave (GW) signals, exerting a notable impact on the processing of GW data. The inference of GW parameters, crucial for GW astronomy research, is particularly susceptible to such interference. In this study, we pioneer the utilization of temporal and time-spectral fusion normalizing flow for likelihood-free inference of GW parameters, seamlessly integrating the high temporal resolution of the time domain with the frequency separation characteristics of both time and frequency domains. Remarkably, our findings indicate that the accuracy of this inference method is comparable to traditional non-glitch sampling techniques. Furthermore, our approach exhibits greater efficiency, boasting processing times on the order of milliseconds. In conclusion, the application of normalizing flow emerges as pivotal in handling GW signals affected by transient noises, offering a promising avenue for enhancing the field of GW astronomy research. △ Less

Submitted 14 March, 2024; v1 submitted 13 December, 2023; originally announced December 2023.

Comments: 13 pages, 10 figures

Journal ref: Chinese Physics C Vol. 48, No. 4 (2024) 045108

A Shock Flash Breaking Out of a Dusty Red Supergiant

Authors: Gaici Li, Maokai Hu, Wenxiong Li, Yi Yang, Xiaofeng Wang, Shengyu Yan, Lei Hu, Jujia Zhang, Yiming Mao, Henrik Riise, Xing Gao, Tianrui Sun, Jialian Liu, Dingrong Xiong, Lifan Wang, Jun Mo, Abdusamatjan Iskandar, Gaobo Xi, Danfeng Xiang, Lingzhi Wang, Guoyou Sun, Keming Zhang, Jian Chen, Weili Lin, Fangzhou Guo , et al. (19 additional authors not shown)

Abstract: Shock breakout emission is light that arises when a shockwave, generated by core-collapse explosion of a massive star, passes through its outer envelope. Hitherto, the earliest detection of such a signal was at several hours after the explosion, though a few others had been reported. The temporal evolution of early light curves should reveal insights into the shock propagation, including explosion… ▽ More Shock breakout emission is light that arises when a shockwave, generated by core-collapse explosion of a massive star, passes through its outer envelope. Hitherto, the earliest detection of such a signal was at several hours after the explosion, though a few others had been reported. The temporal evolution of early light curves should reveal insights into the shock propagation, including explosion asymmetry and environment in the vicinity, but this has been hampered by the lack of multiwavelength observations. Here we report the instant multiband observations of a type II supernova (SN 2023ixf) in the galaxy M101 (at a distance of 6.85+/-0.15 Mpc), beginning at about 1.4 hours after the explosion. The exploding star was a red supergiant with a radius of about 440 solar radii. The light curves evolved rapidly, on timescales of 1-2 hours, and appeared unusually fainter and redder than predicted by models within the first few hours, which we attribute to an optically thick dust shell before it was disrupted by the shockwave. We infer that the breakout and perhaps the distribution of the surrounding dust were not spherically symmetric. △ Less

Submitted 1 April, 2024; v1 submitted 24 November, 2023; originally announced November 2023.

Comments: 32 pages, 9 figures, and 3 tables. Online publication in Nature (Dec. 13th 2023)

Journal ref: Nature volume 627, pages 754-758 (2024)

Probing Thermal Electrons in GRB Afterglows

Authors: Hao-Xuan Gao, Jin-Jun Geng, Tian-Rui Sun, Liang Li, Yong-Feng Huang, Xue-Feng Wu

Abstract: Particle-in-cell simulations have unveiled that shock-accelerated electrons do not follow a pure power-law distribution, but have an additional low-energy "thermal" part, which owns a considerable portion of the total energy of electrons. Investigating the effects of these thermal electrons on gamma-ray burst (GRB) afterglows may provide valuable insights into the particle acceleration mechanisms.… ▽ More Particle-in-cell simulations have unveiled that shock-accelerated electrons do not follow a pure power-law distribution, but have an additional low-energy "thermal" part, which owns a considerable portion of the total energy of electrons. Investigating the effects of these thermal electrons on gamma-ray burst (GRB) afterglows may provide valuable insights into the particle acceleration mechanisms. We solve the continuity equation of electrons in the energy space, from which multi-wavelength afterglows are derived by incorporating processes including synchrotron radiation, synchrotron self-absorption, synchrotron self-Compton scattering, and gamma-gamma annihilation. First, there is an underlying positive correlation between temporal and spectral indices due to the cooling of electrons. Moreover, thermal electrons would result in the simultaneous non-monotonic variation in both spectral and temporal indices at multi-wavelength, which could be individually recorded by the 2.5-meter Wide Field Survey Telescope and Vera Rubin Observatory Legacy Survey of Space and Time (LSST). The thermal electrons could also be diagnosed from afterglow spectra by synergy observation in the optical (with LSST) and X-ray bands (with the Microchannel X-ray Telescope on board the Space Variable Objects Monitor). Finally, we use Monte Carlo simulations to obtain the distribution of peak flux ratio ($R_{\rm X}$) between soft and hard X-rays, and of the time delay ($Δt$) between peak times of soft X-ray and optical light curves. The thermal electrons significantly raise the upper limits of both $R_{\rm X}$ and $Δt$. Thus the distribution of GRB afterglows with thermal electrons is more dispersive in the $R_{\rm X} - Δt$ plane. △ Less

Submitted 10 June, 2024; v1 submitted 10 November, 2023; originally announced November 2023.

Comments: 19 pages, 18 figures, accepted by the Astrophysical Journal

Potential Impact of the Sagittarius Dwarf Galaxy on the Formation of Young O-rich Stars

Authors: Tiancheng Sun, Shaolan Bi, Xunzhou Chen, Yuqin Chen, Yuxi, Lu, Chao Liu, Tobias Buck, Xianfei Zhang, Tanda Li, Yaguang Li, Yaqian Wu, Zhishuai Ge, Lifei Ye

Abstract: The Milky Way underwent significant transformations in its early history, characterised by violent mergers and satellite galaxy accretion. However, recent observations reveal notable star formation events over the past 4 Gyr, likely triggered by perturbations from the Sagittarius dwarf galaxy. Here, we present chemical signatures of this accretion event, using the [Fe/H] (metallicity) and [O/Fe] (… ▽ More The Milky Way underwent significant transformations in its early history, characterised by violent mergers and satellite galaxy accretion. However, recent observations reveal notable star formation events over the past 4 Gyr, likely triggered by perturbations from the Sagittarius dwarf galaxy. Here, we present chemical signatures of this accretion event, using the [Fe/H] (metallicity) and [O/Fe] (oxygen abundance) ratios of thin-disc stars. In the normalised age-metallicity plane, we identify a discontinuous V-shape structure at z$_{\rm max}$ (maximum vertical distance from the disc plane) $<$ 0.4 kpc in the local disc, interrupted by a star formation burst between 4 and 2 Gyr ago. This event is characterised by a significant increase in oxygen abundance, resulting in a distinct [O/Fe] gradient and the formation of young O-rich stars. These stars have larger birth radii, indicating formation in the outer disc followed by radial migration to the Solar neighbourhood. Simulations of late satellite infall suggest that the passage of the Sagittarius dwarf galaxy may have contributed to the observed increase in oxygen abundance in the local disc. △ Less

Submitted 2 April, 2025; v1 submitted 9 November, 2023; originally announced November 2023.

Comments: 18 pages, 10 figures. Published in Nature Communications

Investigating 16 Open Clusters in the Kepler/K2-Gaia DR3 field. I. Membership, Binary, and Rotation

Authors: Liu Long, Shanlao Bi, Jinhua Zhang, Xianfei Zhang, Liyun Zhang, Zhishuai Ge, Tanda Li, Xunzhou Chen, Yaguang Li, Lifei Ye, TianCheng Sun, Jianzhao Zhou

Abstract: Using data from the Gaia Data Release 3 (Gaia DR3) and Kepler/K2, we present a catalog of 16 open clusters with ages ranging from 4 to 4000 Myr, which provides detailed information on membership, binary systems, and rotation. We assess the memberships in 5D phase space, and estimate the basic parameters of each cluster. Among the 20,160 members, there are 4,381 stars identified as binary candidate… ▽ More Using data from the Gaia Data Release 3 (Gaia DR3) and Kepler/K2, we present a catalog of 16 open clusters with ages ranging from 4 to 4000 Myr, which provides detailed information on membership, binary systems, and rotation. We assess the memberships in 5D phase space, and estimate the basic parameters of each cluster. Among the 20,160 members, there are 4,381 stars identified as binary candidates and 49 stars as blue straggler stars. The fraction of binaries vary in each cluster, and the range between 9% to 44%. We obtain the rotation periods of 5,467 members, of which 4,304 are determined in this work. To establish a benchmark for the rotation-age-color relation, we construct color-period diagrams. We find that the rotational features of binaries are similar to that of single stars, while features for binaries are more scattered in the rotation period. Moreover, the morphology of the color-period relationship is already established for Upper Scorpius at the age of 19 Myr, and some stars of varying spectral types (i.e. FG-, K-, and M-type) show different spin-down rates after the age of ~110 Myr. By incorporating the effects of stalled spin-down into our analysis, we develop an empirical rotation-age-color relation, which is valid with ages between 700 - 4000 Myr and colors corresponding to a range of 0.5 < (G_BP-G_RP)0 < 2.5 mag. △ Less

Submitted 13 July, 2023; originally announced July 2023.

Comments: 21 pages, 17 figures, accepted for publication in ApJS

Age of FGK Dwarfs Observed with LAMOST and GALAH: Considering the Oxygen Enhancement

Authors: Tiancheng Sun, Zhishuai Ge, Xunzhou Chen, Shaolan Bi, Tanda Li, Xianfei Zhang, Yaguang Li, Yaqian Wu, Sarah A. Bird, Ferguson J. W., Jianzhao Zhou, Lifei Ye, Liu Long, Jinghua Zhang

Abstract: Varying oxygen abundance could impact the modeling-inferred ages. This work aims to estimate the ages of dwarfs considering observed oxygen abundance. To characterize 67,503 LAMOST and 4,006 GALAH FGK-type dwarf stars, we construct a grid of stellar models which take into account oxygen abundance as an independent model input. Compared with ages determined with commonly-used $α$-enhanced models, w… ▽ More Varying oxygen abundance could impact the modeling-inferred ages. This work aims to estimate the ages of dwarfs considering observed oxygen abundance. To characterize 67,503 LAMOST and 4,006 GALAH FGK-type dwarf stars, we construct a grid of stellar models which take into account oxygen abundance as an independent model input. Compared with ages determined with commonly-used $α$-enhanced models, we find a difference of $\sim$9% on average when the observed oxygen abundance is considered. The age differences between the two types of models are correlated to [Fe/H] and [O/$α$], and they are relatively significant on stars with [Fe/H] $\lesssim$ -0.6 dex. Generally, varying 0.2 dex in [O/$α$] will alter the age estimates of metal-rich (-0.2 $<$ [Fe/H] $<$ 0.2) stars by $\sim$10%, and relatively metal-poor (-1 $<$ [Fe/H] $<$ -0.2) stars by $\sim$15%. Of the low-O stars with [Fe/H] $<$ 0.1 dex and [O/$α$] $\sim$ -0.2 dex, many have fractional age differences of $\geq$ 10%, and even reach up to 27%. The fractional age difference of high-O stars with [O/$α$] $\sim$ 0.4 dex reaches up to -33% to -42% at [Fe/H] $\lesssim$ -0.6 dex. We also analyze the chemical properties of these stars. We find a decreasing trend of [Fe/H] with age from 7.5-9 Gyr to 5-6.5 Gyr for the stars from the LAMOST and GALAH. The [O/Fe] of these stars increases with decreasing age from 7.5-9 Gyr to 3-4 Gyr, indicating that the younger population is more O-rich. △ Less

Submitted 8 July, 2023; originally announced July 2023.

Comments: 18 pages, 12 figures, accepted for publication in ApJS

Sciences with the 2.5-meter Wide Field Survey Telescope (WFST)

Authors: WFST Collaboration, Tinggui Wang, Guilin Liu, Zhenyi Cai, Jinjun Geng, Min Fang, Haoning He, Ji-an Jiang, Ning Jiang, Xu Kong, Bin Li, Ye Li, Wentao Luo, Zhizheng Pan, Xuefeng Wu, Ji Yang, Jiming Yu, Xianzhong Zheng, Qingfeng Zhu, Yi-Fu Cai, Yuanyuan Chen, Zhiwei Chen, Zigao Dai, Lulu Fan, Yizhong Fan , et al. (38 additional authors not shown)

Abstract: The Wide Field Survey Telescope (WFST) is a dedicated photometric surveying facility being built jointly by the University of Science and Technology of China and the Purple Mountain Observatory. It is equipped with a 2.5-meter diameter primary mirror, an active optics system, and a mosaic CCD camera with 0.73 gigapixels on the primary focal plane for high-quality image capture over an FOV of 6.5-s… ▽ More The Wide Field Survey Telescope (WFST) is a dedicated photometric surveying facility being built jointly by the University of Science and Technology of China and the Purple Mountain Observatory. It is equipped with a 2.5-meter diameter primary mirror, an active optics system, and a mosaic CCD camera with 0.73 gigapixels on the primary focal plane for high-quality image capture over an FOV of 6.5-square-degree. It is anticipated that WFST will be set up at the Lenghu site in the summer of 2023 and begin to observe the northern sky in four optical bands (u, g, r, and i) with a range of cadences, from hourly/daily in the Deep High-Cadence Survey (DHS) program to semiweekly in the Wide-Field Survey (WFS) program, three months later. During a photometric night, a nominal 30 s exposure in the WFS program will reach a depth of 22.27, 23.32, 22.84, and 22.31 (AB magnitudes) in these four bands, respectively, allowing for the detection of a tremendous amount of transients in the low-z universe and a systematic investigation of the variability of Galactic and extragalactic objects. In the DHS program, intranight 90 s exposures as deep as 23 (u) and 24 mag (g), in combination with target of opportunity follow-ups, will provide a unique opportunity to explore energetic transients in demand for high sensitivities, including the electromagnetic counterparts of gravitational wave events, supernovae within a few hours of their explosions, tidal disruption events and fast, luminous optical transients even beyond a redshift of unity. In addition, the final 6-year co-added images, anticipated to reach g=25.8 mag in WFS or 1.5 mags deeper in DHS, will be of fundamental importance to general Galactic and extragalactic science. The highly uniform legacy surveys of WFST will serve as an indispensable complement to those of LSST that monitor the southern sky. △ Less

Submitted 14 September, 2023; v1 submitted 13 June, 2023; originally announced June 2023.

Comments: 48 pages

Journal ref: SCPMA-Vol. 66 No. 10: 109512 (2023)

Rapid identification of time-frequency domain gravitational wave signals from binary black holes using deep learning

Authors: Yu-Xin Wang, Shang-Jie Jin, Tian-Yang Sun, Jing-Fei Zhang, Xin Zhang

Abstract: Recent developments in deep learning techniques have offered an alternative and complementary approach to traditional matched filtering methods for the identification of gravitational wave (GW) signals. The rapid and accurate identification of GW signals is crucial for the progress of GW physics and multi-messenger astronomy, particularly in light of the upcoming fourth and fifth observing runs of… ▽ More Recent developments in deep learning techniques have offered an alternative and complementary approach to traditional matched filtering methods for the identification of gravitational wave (GW) signals. The rapid and accurate identification of GW signals is crucial for the progress of GW physics and multi-messenger astronomy, particularly in light of the upcoming fourth and fifth observing runs of LIGO-Virgo-KAGRA. In this work, we use the 2D U-Net algorithm to identify the time-frequency domain GW signals from stellar-mass binary black hole (BBH) mergers. We simulate BBH mergers with component masses from 5 to 80 $M_{\odot}$ and account for the LIGO detector noise. We find that the GW events in the first and second observation runs could all be clearly and rapidly identified. For the third observing run, about $80\%$ GW events could be identified. In particular, GW190814, currently unknown, is a special case that can be identified by the network, while other binary neutron star mergers and neutron star-black hole mergers can not be identified. Compared to the traditional convolutional neural network, the U-Net algorithm can output the time-frequency domain signal images rather than probabilities, providing a more intuitive investigation. Moreover, some of the results through U-Net can provide preliminary inference on the chirp mass information. In conclusion, the U-Net algorithm can rapidly identify the time-frequency domain GW signals from BBH mergers and potentially be helpful for future parameter inferences. △ Less

Submitted 1 November, 2024; v1 submitted 30 May, 2023; originally announced May 2023.

Comments: 15 pages, 11 figures

Journal ref: Chin. Phys. C 48, no. 12, 125107 (2024)

The Lobster Eye Imager for Astronomy Onboard the SATech-01 Satellite

Authors: Z. X. Ling, X. J. Sun, C. Zhang, S. L. Sun, G. Jin, S. N. Zhang, X. F. Zhang, J. B. Chang, F. S. Chen, Y. F. Chen, Z. W. Cheng, W. Fu, Y. X. Han, H. Li, J. F. Li, Y. Li, Z. D. Li, P. R. Liu, Y. H. Lv, X. H. Ma, Y. J. Tang, C. B. Wang, R. J. Xie, Y. L. Xue, A. L. Yan , et al. (101 additional authors not shown)

Abstract: The Lobster Eye Imager for Astronomy (LEIA), a pathfinder of the Wide-field X-ray Telescope of the Einstein Probe (EP) mission, was successfully launched onboard the SATech-01 satellite of the Chinese Academy of Sciences on 27 July 2022. In this paper, we introduce the design and on-ground test results of the LEIA instrument. Using state-of-the-art Micro-Pore Optics (MPO), a wide field-of-view (Fo… ▽ More The Lobster Eye Imager for Astronomy (LEIA), a pathfinder of the Wide-field X-ray Telescope of the Einstein Probe (EP) mission, was successfully launched onboard the SATech-01 satellite of the Chinese Academy of Sciences on 27 July 2022. In this paper, we introduce the design and on-ground test results of the LEIA instrument. Using state-of-the-art Micro-Pore Optics (MPO), a wide field-of-view (FoV) of 346 square degrees (18.6 degrees * 18.6 degrees) of the X-ray imager is realized. An optical assembly composed of 36 MPO chips is used to focus incident X-ray photons, and four large-format complementary metal-oxide semiconductor (CMOS) sensors, each of 6 cm * 6 cm, are used as the focal plane detectors. The instrument has an angular resolution of 4 - 8 arcmin (in FWHM) for the central focal spot of the point spread function, and an effective area of 2 - 3 cm2 at 1 keV in essentially all the directions within the field of view. The detection passband is 0.5 - 4 keV in the soft X-rays and the sensitivity is 2 - 3 * 10-11 erg s-1 cm-2 (about 1 mini-Crab) at 1,000 second observation. The total weight of LEIA is 56 kg and the power is 85 W. The satellite, with a design lifetime of 2 years, operates in a Sun-synchronous orbit of 500 km with an orbital period of 95 minutes. LEIA is paving the way for future missions by verifying in flight the technologies of both novel focusing imaging optics and CMOS sensors for X-ray observation, and by optimizing the working setups of the instrumental parameters. In addition, LEIA is able to carry out scientific observations to find new transients and to monitor known sources in the soft X-ray band, albeit limited useful observing time available. △ Less

Submitted 24 May, 2023; originally announced May 2023.

Comments: Accepted by RAA

Characterising abundance-age relations of GALAH stars using oxygen-enhanced stellar models

Authors: Tiancheng Sun, Xunzhou Chen, Shaolan Bi, Zhishuai Ge, Maosheng Xiang, Yaqian Wu

Abstract: Main Sequence Turn-off stars (MSTO) and subgiant stars are good tracers of galactic populations. We present a study of 41,034 MSTO and subgiant stars from the GALAH survey. Using a grid of stellar models that accounts for the variation of O abundances, we determine their ages with a median age uncertainty of $\sim$9.4 per cent. Our analysis reveals that the ages of high-O stars based on O-enhanced… ▽ More Main Sequence Turn-off stars (MSTO) and subgiant stars are good tracers of galactic populations. We present a study of 41,034 MSTO and subgiant stars from the GALAH survey. Using a grid of stellar models that accounts for the variation of O abundances, we determine their ages with a median age uncertainty of $\sim$9.4 per cent. Our analysis reveals that the ages of high-O stars based on O-enhanced models (OEM models) are smaller than those determined with $α$-enhanced models, resulting in a mean fractional age difference of -5.3 per cent at [O/$α$] = 0.2 and -11.0 per cent at [O/$α$] = 0.4. This age difference significantly impacts the age distribution of thick disc and halo stars, leading to a steeper downward trend in the [Fe/H]-age plane from 8 Gyr to 14 Gyr, indicating a shorter formation time-scale and a faster chemical-enhanced history for these populations. We confirm the V-shape of the normalized age-metallicity distribution $p$($τ$$\mid$[Fe/H]) of thin disc stars, which is presumably a consequence of the second gas infall. Additionally, we find that the halo stars in our sample can be divided into two sequences, a metal-rich sequence (Splash stars) and a metal-poor sequence (accreted stars), with the Splash stars predominantly older than 9 Gyr and the accreted halo stars older than 10 Gyr. Finally, we observe two distinct sequences in the relations between various chemical abundances and age for disc stars, namely a young sequence with ages $<$ $\sim$8 Gyr and an old sequence with ages $>$ $\sim$8 Gyr. △ Less

Submitted 15 May, 2023; originally announced May 2023.

Comments: 11 pages, 12 figures

Non-radial oscillations and gravitational wave emission of hybrid neutron stars

Authors: Zi-Yue Zheng, Ting-Ting Sun, Huan Chen, Jin-Biao Wei, G. F. Burgio, H. -J. Schulze

Abstract: We investigate non-radial oscillations of pure and hybrid neutron stars, employing equations of state of nuclear matter from Brueckner-Hartree-Fock theory, and of quark matter from the Dyson-Schwinger quark model, performing a Gibbs construction for the mixed phase in hybrid stars. Characteristic differences between neutron-star and hybrid-star $g_1$-mode oscillation frequencies, damping times, an… ▽ More We investigate non-radial oscillations of pure and hybrid neutron stars, employing equations of state of nuclear matter from Brueckner-Hartree-Fock theory, and of quark matter from the Dyson-Schwinger quark model, performing a Gibbs construction for the mixed phase in hybrid stars. Characteristic differences between neutron-star and hybrid-star $g_1$-mode oscillation frequencies, damping times, and gravitational wave strains are pointed out. Prospects of observations are also discussed. △ Less

Submitted 13 March, 2023; originally announced March 2023.

Comments: 11 pages, 8 figures

X-ray morphology due to charge-exchange emissions used to study the global structure around Mars

Authors: G. Y. Liang, T. R. Sun, H. Y. Lu, X. L. Zhu, Y. Wu, S. B. Li, H. G. Wei, D. W. Yuan, W. Cui, X. W. Ma, G. Zhao

Abstract: Soft x-ray emissions induced by solar wind ions that collide with neutral material in the solar system have been detected around planets, and were proposed as a remote probe for the solar wind interaction with the Martian exosphere. A multi-fluid three-dimensional magneto-hydrodynamic model is adopted to derive the global distributions of solar wind particles. Spherically symmetric exospheric H, H… ▽ More Soft x-ray emissions induced by solar wind ions that collide with neutral material in the solar system have been detected around planets, and were proposed as a remote probe for the solar wind interaction with the Martian exosphere. A multi-fluid three-dimensional magneto-hydrodynamic model is adopted to derive the global distributions of solar wind particles. Spherically symmetric exospheric H, H$_2$, He, O, and CO$_2$ density profiles and a sophisticated hybrid model that includes charge-exchange and proton/neutral excitation processes are used to study the low triplet line ratio $G=\frac{i+f}{r}$ (0.77$\pm$0.58) of O VII and total x-ray luminosity around Mars. We further calculate the emission factor $α$-value with different neutrals over a wide ion abundance and velocity ranges. Our results are in good agreement with those of previous reports. The evolution of the charge stage of solar wind ions shows that sequential recombination due to charge-exchange can be negligible at the interaction region. This only appears below the altitude of 400~km. The anonymous low disk $G$ ratio can be easily explained by the collisional quenching effect at neutral densities higher than 10$^{11}$cm$^{-3}$. However, the quenching contribution is small in Mars' exosphere and only appears below 400~km. Charge-exchange with H$_2$ and N$_2$ is still the most likely reason for this low $G$-ratio. X-ray emissivity maps in collisions with different neutrals differ from each other. A clear bow shock in the collision with all the neutrals is in accordance with previous reports. The resulting total x-ray luminosity of 6.55~MW shows a better agreement with the XMM-Newton observation of 12.8$\pm$1.4~MW than that of previous predictions. △ Less

Submitted 19 December, 2022; originally announced December 2022.

Comments: 17 pages, 13 figures; Accpted by ApJ

ET White Paper: To Find the First Earth 2.0

Authors: Jian Ge, Hui Zhang, Weicheng Zang, Hongping Deng, Shude Mao, Ji-Wei Xie, Hui-Gen Liu, Ji-Lin Zhou, Kevin Willis, Chelsea Huang, Steve B. Howell, Fabo Feng, Jiapeng Zhu, Xinyu Yao, Beibei Liu, Masataka Aizawa, Wei Zhu, Ya-Ping Li, Bo Ma, Quanzhi Ye, Jie Yu, Maosheng Xiang, Cong Yu, Shangfei Liu, Ming Yang , et al. (142 additional authors not shown)

Abstract: We propose to develop a wide-field and ultra-high-precision photometric survey mission, temporarily named "Earth 2.0 (ET)". This mission is designed to measure, for the first time, the occurrence rate and the orbital distributions of Earth-sized planets. ET consists of seven 30cm telescopes, to be launched to the Earth-Sun's L2 point. Six of these are transit telescopes with a field of view of 500… ▽ More We propose to develop a wide-field and ultra-high-precision photometric survey mission, temporarily named "Earth 2.0 (ET)". This mission is designed to measure, for the first time, the occurrence rate and the orbital distributions of Earth-sized planets. ET consists of seven 30cm telescopes, to be launched to the Earth-Sun's L2 point. Six of these are transit telescopes with a field of view of 500 square degrees. Staring in the direction that encompasses the original Kepler field for four continuous years, this monitoring will return tens of thousands of transiting planets, including the elusive Earth twins orbiting solar-type stars. The seventh telescope is a 30cm microlensing telescope that will monitor an area of 4 square degrees toward the galactic bulge. This, combined with simultaneous ground-based KMTNet observations, will measure masses for hundreds of long-period and free-floating planets. Together, the transit and the microlensing telescopes will revolutionize our understandings of terrestrial planets across a large swath of orbital distances and free space. In addition, the survey data will also facilitate studies in the fields of asteroseismology, Galactic archeology, time-domain sciences, and black holes in binaries. △ Less

Submitted 14 June, 2022; originally announced June 2022.

Comments: 116 pages,79 figures

Antarctic Survey Telescope 3-3: Overview, System Performance and Preliminary Observations at Yaoan, Yunnan

Authors: Tianrui Sun, Xiaoyan Li, Lei Hu, Kelai Meng, Zijian Han, Maokai Hu, Zhengyang Li, Haikun Wen, Fujia Du, Shihai Yang, Bozhong Gu, Xiangyan Yuan, Yun Li, Huihui Wang, Lei Liu, Zhenxi Zhu, Xuehai Huang, Chengming Lei, Lifan Wang, Xuefeng Wu

Abstract: The third Antarctic Survey Telescope array instrument at Dome A in Antarctica, the AST3-3 telescope, has been in commissioning from March 2021. We deployed AST3-3 at the Yaoan astronomical station in Yunnan Province for an automatic time-domain survey and follow-up observations with an optimised observation and protection system. The telescope system of AST3-3 is similar to that of AST3-1 and AST3… ▽ More The third Antarctic Survey Telescope array instrument at Dome A in Antarctica, the AST3-3 telescope, has been in commissioning from March 2021. We deployed AST3-3 at the Yaoan astronomical station in Yunnan Province for an automatic time-domain survey and follow-up observations with an optimised observation and protection system. The telescope system of AST3-3 is similar to that of AST3-1 and AST3-2, except that it is equipped with a 14K~$ \times$~10K QHY411 CMOS camera. AST3-3 has a field of view of $1.65^\circ \times 1.23^\circ$ and is currently using the $g$ band filter. During commissioning at Yaoan, AST3-3 aims to conduct an extragalactic transient survey, coupled with prompt follow-ups of opportunity targets. In this paper, we present the architecture of the AST3-3 automatic observation system. We demonstrate the data processing of observations by representatives SN 2022eyw and GRB 210420B. △ Less

Submitted 13 June, 2022; v1 submitted 7 June, 2022; originally announced June 2022.

Comments: 20 pages, 15 figures

Multi-wavelength study of the luminous GRB 210619B observed with Fermi and ASIM

Authors: M. D. Caballero-García, Rahul Gupta, S. B. Pandey, S. R. Oates, M. Marisaldi, A. Ramsli, Y. -D. Hu, A. J. Castro-Tirado, R. Sánchez-Ramírez, P. H. Connell, F. Christiansen, A. Kumar Ror, A. Aryan, J. -M. Bai, M. A. Castro-Tirado, Y. -F. Fan, E. Fernández-García, A. Kumar, A. Lindanger, A. Mezentsev, J. Navarro-González, T. Neubert, N. Østgaard, I. Pérez-García, V. Reglero , et al. (6 additional authors not shown)

Abstract: We report on detailed multi-wavelength observations and analysis of the very bright and long GRB 210619B, detected by the Atmosphere-Space Interactions Monitor (ASIM) installed on the International Space Station (ISS) and the Gamma-ray Burst Monitor (GBM) on-board the Fermi mission. Our main goal is to understand the radiation mechanisms and jet composition of GRB 210619B. With a measured redshift… ▽ More We report on detailed multi-wavelength observations and analysis of the very bright and long GRB 210619B, detected by the Atmosphere-Space Interactions Monitor (ASIM) installed on the International Space Station (ISS) and the Gamma-ray Burst Monitor (GBM) on-board the Fermi mission. Our main goal is to understand the radiation mechanisms and jet composition of GRB 210619B. With a measured redshift of $z$ = 1.937, we find that GRB 210619B falls within the 10 most luminous bursts observed by Fermi so far. The energy-resolved prompt emission light curve of GRB 210619B exhibits an extremely bright hard emission pulse followed by softer/longer emission pulses. The low-energy photon indices ($α_{\rm pt}$) values obtained using the time-resolved spectral analysis of the burst suggest a transition between the thermal (during harder pulse) to non-thermal (during softer pulse) outflow. We examine the correlation between spectral parameters and find that both peak energy and $α_{\rm pt}$ exhibit the flux tracking pattern. The late time broadband photometric dataset can be explained within the framework of the external forward shock model with $ν_m$ $< ν_c$ $< ν_{x}$ (where $ν_m$, $ν_c$, and $ν_{x}$ are the synchrotron peak, cooling-break, and X-ray frequencies, respectively) spectral regime supporting a rarely observed hard electron energy index ($p<$ 2). We find moderate values of host extinction of E(B-V) = 0.14 $\pm$ 0.01 mag for the Small Magellanic Cloud (SMC) extinction law. In addition, we also report late-time optical observations with the 10.4 m GTC placing deep upper limits for the host galaxy ($z$=1.937), favouring a faint, dwarf host for the burst. △ Less

Submitted 5 December, 2022; v1 submitted 16 May, 2022; originally announced May 2022.

Comments: 24 pages, 18 figures, 10 tables, accepted for publication in MNRAS

Pipeline for Antarctic Survey Telescope 3-3 in Yaoan, Yunnan

Authors: Tianrui Sun, Lei Hu, Songbo Zhang, Xiaoyan Li, Kelai Meng, Xuefeng Wu, Lifan Wang, A. J. Castro-Tirado

Abstract: AST3-3 is the third robotic facility of the Antarctic Survey Telescopes (AST3) for transient surveys to be deployed at Dome A, Antarctica. Due to the current pandemic, the telescope has been currently deployed at the Yaoan Observation Station in China, starting the commissioning observation and a transient survey. This paper presents a fully automatic data processing system for AST3-3 observations… ▽ More AST3-3 is the third robotic facility of the Antarctic Survey Telescopes (AST3) for transient surveys to be deployed at Dome A, Antarctica. Due to the current pandemic, the telescope has been currently deployed at the Yaoan Observation Station in China, starting the commissioning observation and a transient survey. This paper presents a fully automatic data processing system for AST3-3 observations. The transient detection pipeline uses state-of-the-art image subtraction techniques optimised for GPU devices. Image reduction and transient photometry are accelerated by concurrent task methods. Our Python-based system allows for transient detection from wide-field data in a real-time and accurate way. A ResNet-based rotational-invariant neural network was employed to classify the transient candidates. As a result, the system enables auto-generation of transients and their light curves. △ Less

Submitted 10 May, 2022; originally announced May 2022.

Comments: 22 pages, 12 figures

Transition edge sensor based detector: from X-ray to $γ$-ray

Authors: Shuo Zhang, Jing-Kai Xia, Tao Sun, Wen-Tao Wu, Bing-Jun Wu, Yong-Liang Wang, Robin Cantor, Ke Han, Xiao-Peng Zhou, Hao-Ran Liu, Fu-You Fan, Si-Ming Guo, Jun-Cheng Liang, De-Hong Li, Yan-Ru Song, Xu-Dong Ju, Qiang Fu, Zhi Liu

Abstract: The Transition Edge Sensor is extremely sensitive to the change of temperature, combined with the high-Z metal of a certain thickness, it can realize the high energy resolution measurement of particles such as X-rays. X-rays with energies below 10 keV have very weak penetrating ability, so only a few microns thick of gold or bismuth can obtain quantum efficiency higher than 70\%. Therefore, the en… ▽ More The Transition Edge Sensor is extremely sensitive to the change of temperature, combined with the high-Z metal of a certain thickness, it can realize the high energy resolution measurement of particles such as X-rays. X-rays with energies below 10 keV have very weak penetrating ability, so only a few microns thick of gold or bismuth can obtain quantum efficiency higher than 70\%. Therefore, the entire structure of the TES X-ray detector in this energy range can be realized in the microfabrication process. However, for X-rays or gamma rays from 10 keV to 200 keV, sub-millimeter absorber layers are required, which cannot be realized by microfabrication process. This paper first briefly introduces a set of TES X-ray detectors and their auxiliary systems built by ShanghaiTech University, then focus on the introduction of the TES $γ$-ray detector, with absorber based on an sub-millimeter lead-tin alloy sphere. The detector has a quantum efficiency above 70\% near 100 keV, and an energy resolution of about 161.5eV@59.5keV. △ Less

Submitted 26 April, 2022; v1 submitted 1 April, 2022; originally announced April 2022.

Comments: 13 pages, 12 figures

MSC Class: 81V35

Diagnosing Circumburst Environment with Multiband Gamma-Ray Burst Radio Afterglows

Authors: Bo Zhang, Liang-Duan Liu, Tian-Rui Sun, Fen Lyu, Xue-Feng Wu

Abstract: It has been widely recognized that gamma-ray burst (GRB) afterglows arise from interactions between GRB outflow and circumburst medium, while their evolution follows the behaviors of relativistic shock waves. Assuming the distribution of circumburst medium follows a general power-law form, that is, $n = A_{\ast} R^{-k}$, where $R$ denotes the distance from the burst, it is obvious that the value o… ▽ More It has been widely recognized that gamma-ray burst (GRB) afterglows arise from interactions between GRB outflow and circumburst medium, while their evolution follows the behaviors of relativistic shock waves. Assuming the distribution of circumburst medium follows a general power-law form, that is, $n = A_{\ast} R^{-k}$, where $R$ denotes the distance from the burst, it is obvious that the value of density-distribution index $k$ can affect the behaviors of the afterglow. In this paper, we analyze the temporal and spectral behaviors of GRB radio afterglows with arbitrary $k$-values. In the radio band, a standard GRB afterglow produced by forward shock exhibits a late-time flux peak, and the relative peak fluxes as well as peak times at different frequencies show dependencies on $k$. Thus with multi-band radio peak observations, one can determine the density profile of circumburst medium by comparing the relations between peak flux/time and frequency at each observing band. Also, the effects of trans-relativistic shock waves, as well as jets in afterglows are discussed. By analyzing 31 long and 1 short GRBs with multi-band data of radio afterglows, we find that nearly half of them can be explained with uniform interstellar medium ($k=0$), $\sim 1/5$ can be constrained to exhibiting stellar wind environment ($k=2$), while less than $\sim 1/3$ samples show $0< k< 2$. △ Less

Submitted 16 March, 2022; originally announced March 2022.

Comments: 26 pages, 9 figures

Journal ref: Published in ApJ, 927:84, 2022

Probing into emission mechanisms of GRB 190530A using time-resolved spectra and polarization studies: Synchrotron Origin?

Authors: Rahul Gupta, S. Gupta, T. Chattopadhyay, V. Lipunov, A. J. Castro-Tirado, D. Bhattacharya, S. B. Pandey, S. R. Oates, Amit Kumar, Y. -D. Hu, A. F. Valeev, P. Yu. Minaev, H. Kumar, J. Vinko, Dimple, V. Sharma, A. Aryan, A. Castellón, A. Gabovich, A. Moskvitin, A. Ordasi, A. Pál, A. Pozanenko, B. -B. Zhang, B. Kumar , et al. (25 additional authors not shown)

Abstract: Multi-pulsed GRB 190530A, detected by the GBM and LAT onboard \fermi, is the sixth most fluent GBM burst detected so far. This paper presents the timing, spectral, and polarimetric analysis of the prompt emission observed using \AstroSat and \fermi to provide insight into the prompt emission radiation mechanisms. The time-integrated spectrum shows conclusive proof of two breaks due to peak energy… ▽ More Multi-pulsed GRB 190530A, detected by the GBM and LAT onboard \fermi, is the sixth most fluent GBM burst detected so far. This paper presents the timing, spectral, and polarimetric analysis of the prompt emission observed using \AstroSat and \fermi to provide insight into the prompt emission radiation mechanisms. The time-integrated spectrum shows conclusive proof of two breaks due to peak energy and a second lower energy break. Time-integrated (55.43 $\pm$ 21.30 \%) as well as time-resolved polarization measurements, made by the Cadmium Zinc Telluride Imager (CZTI) onboard \AstroSat, show a hint of high degree of polarization. The presence of a hint of high degree of polarization and the values of low energy spectral index ($α_{\rm pt}$) do not run over the synchrotron limit for the first two pulses, supporting the synchrotron origin in an ordered magnetic field. However, during the third pulse, $α_{\rm pt}$ exceeds the synchrotron line of death in few bins, and a thermal signature along with the synchrotron component in the time-resolved spectra is observed. Furthermore, we also report the earliest optical observations constraining afterglow polarization using the MASTER (P $<$ 1.3 \%) and the redshift measurement ($z$= 0.9386) obtained with the 10.4m GTC telescopes. The broadband afterglow can be described with a forward shock model for an ISM-like medium with a wide jet opening angle. We determine a circumburst density of $n_{0} \sim$ 7.41, kinetic energy $E_{\rm K} \sim$ 7.24 $\times 10^{54}$ erg, and radiated $γ$-ray energy $E_{\rm γ, iso} \sim$ 6.05 $\times 10^{54}$ erg, respectively. △ Less

Submitted 4 January, 2022; originally announced January 2022.

Comments: 28 pages, 17 figures, accepted for publication in MNRAS

81 New Candidate Fast Radio Bursts in Parkes Archive

Authors: X. Yang, S. -B. Zhang, J. -S. Wang, G. Hobbs, T. -R. Sun, R. N. Manchester, J. -J. Geng, C. J. Russell, R. Luo, Z. -F. Tang, C. Wang, J. -J. Wei, L. Staveley-Smith, S. Dai, Y. Li, Y. -Y. Yang, X. -F. Wu

Abstract: We have searched for weak fast radio burst (FRB) events using a database containing 568,736,756 transient events detected using the Parkes radio telescope between 1997 and 2001. In order to classify these pulses, and to identify likely FRB candidates, we used a machine learning algorithm based on ResNet. We identified 81 new candidate FRBs and provide details of their positions, event times, and d… ▽ More We have searched for weak fast radio burst (FRB) events using a database containing 568,736,756 transient events detected using the Parkes radio telescope between 1997 and 2001. In order to classify these pulses, and to identify likely FRB candidates, we used a machine learning algorithm based on ResNet. We identified 81 new candidate FRBs and provide details of their positions, event times, and dispersion measures. These events were detected in only one beam of the Parkes multibeam receiver. We used a relatively low S/N cutoff threshold when selecting these bursts and some have dispersion measures only slightly exceeding the expected Galactic contribution. We therefore present these candidate FRBs as a guide for follow-up observations in the search for repeating FRBs. △ Less

Submitted 31 August, 2021; v1 submitted 1 August, 2021; originally announced August 2021.

Comments: 8 pages, 5 figures, 2 tables, accepted by MNRAS

Investigation of the particle-particle interaction effects in the cosmic Zevatron based on cyclotron auto-resonance by particle-in-cell simulations

Authors: Yousef I. Salamin, Qian Zhao, Ting Sun

Abstract: Cyclotron autoresonance acceleration has been recently advanced as a potential mechanism for accelerating nuclei to ZeV energies (1 ZeV = $10^{21}$ eV). All results have been based on single- and many-particle calculations employing analytic solutions to the relativistic equations of motion in the combined magnetic and radiation fields, excluding effects related to the particle-particle interactio… ▽ More Cyclotron autoresonance acceleration has been recently advanced as a potential mechanism for accelerating nuclei to ZeV energies (1 ZeV = $10^{21}$ eV). All results have been based on single- and many-particle calculations employing analytic solutions to the relativistic equations of motion in the combined magnetic and radiation fields, excluding effects related to the particle-particle interactions. Here, results from many-particle calculations and Particle-In-Cell (PIC) simulations, are presented which lend support to the single-particle investigations. Each single-particle result is found to lie well within one standard deviation about the ensemble average obtained from the corresponding many-particle calculation. The PIC simulations show that, even for number densities far exceeding those employed in the non-interacting case, the energy gain drops markedly due to the particle-particle interactions, over the first $\sim 8~ mm$ of the acceleration length. Together with the substantial attenuation, this finding supports the conclusion that the particle-particle interaction effects can be negligibly small over acceleration lengths of typically many kilometers. △ Less

Submitted 17 November, 2022; v1 submitted 10 June, 2021; originally announced June 2021.

Optical and Ultraviolet Monitoring of the Black Hole X-ray Binary MAXI J1820+070/ASASSN-18ey for 18 Months

Authors: Hanna Sai, Xiaofeng Wang, Jianfeng Wu, Jie Lin, Hua Feng, Tianmeng Zhang, Wenxiong Li, Jujia Zhang, Jun Mo, Tianrui Sun, Shuhrat A. Ehgamberdiev, Davron Mirzaqulov, Liming Rui, Weili Lin, Xulin Zhao, Han Lin, Jicheng Zhang, Xinghan Zhang, Yong Zhao, Xue Li, Danfeng Xiang, Lingzhi Wang, Chengyuan Wu

Abstract: MAXI J1820+070 is a low-mass black hole X-ray binary system with high luminosity in both optical and X-ray bands during the outburst periods. We present extensive photometry in X-ray, ultraviolet, and optical bands, as well as densely-cadenced optical spectra, covering the phase from the beginning of optical outburst to $\sim$550 days. During the rebrightening process, the optical emission precede… ▽ More MAXI J1820+070 is a low-mass black hole X-ray binary system with high luminosity in both optical and X-ray bands during the outburst periods. We present extensive photometry in X-ray, ultraviolet, and optical bands, as well as densely-cadenced optical spectra, covering the phase from the beginning of optical outburst to $\sim$550 days. During the rebrightening process, the optical emission preceded the X-ray by 20.80 $\pm$ 2.85 days. The spectra are characterized by blue continua and emission features of Balmer series, He I, He II lines and broad Bowen blend. The pseudo equivalent width (pEW) of emission lines are found to show anticorrelations with the X-ray flux measured at comparable phases, which is due to the increased suppression by the optical continuum. At around the X-ray peak, the full width at half maximums (FWHMs) of H$_β$ and He II $λ$4686 tend to stabilize at 19.4 Angstrom and 21.8 Angstrom, which corresponds to the line forming region at a radius of 1.7 and 1.3 R_sun within the disk. We further analyzed the absolute fluxes of the lines and found that the fluxes of H$_β$ and He II $λ$4686 show positive correlations with the X-ray flux, favoring that the irradiation model is responsible for the optical emission. However, the fact that X-ray emission experiences a dramatic flux drop at t$\sim$200 days after the outburst, while the optical flux only shows little variations suggests that additional energy such as viscous energy may contribute to the optical radiation in addition to the X-ray irradiation. △ Less

Submitted 21 April, 2021; originally announced April 2021.

Comments: Accepted for publication in MNRAS

MHD Modeling of Solar Coronal Magnetic Evolution Driven by Photospheric Flow

Authors: Chaowei Jiang, Xinkai Bian, Tingting Sun, Xueshang Feng

Abstract: It is well known that magnetic fields dominate the dynamics in the solar corona, and new generation of numerical modelling of the evolution of coronal magnetic fields, as featured with boundary conditions driven directly by observation data, are being developed. This paper describes a new approach of data-driven magnetohydrodynamic (MHD) simulation of solar active region (AR) magnetic field evolut… ▽ More It is well known that magnetic fields dominate the dynamics in the solar corona, and new generation of numerical modelling of the evolution of coronal magnetic fields, as featured with boundary conditions driven directly by observation data, are being developed. This paper describes a new approach of data-driven magnetohydrodynamic (MHD) simulation of solar active region (AR) magnetic field evolution, which is for the first time that a data-driven full-MHD model utilizes directly the photospheric velocity field from DAVE4VM. We constructed a well-established MHD equilibrium based on a single vector magnetogram by employing an MHD-relaxation approach with sufficiently small kinetic viscosity, and used this MHD equilibrium as the initial conditions for subsequent data-driven evolution. Then we derived the photospheric surface flows from a time series of observed magentograms based on the DAVE4VM method. The surface flows are finally inputted in time sequence to the bottom boundary of the MHD model to self-consistently update the magnetic field at every time step by solving directly the magnetic induction equation at the bottom boundary. We applied this data-driven model to study the magnetic field evolution of AR 12158 with SDO/HMI vector magnetograms. Our model reproduced a quasi-static stress of the field lines through mainly the rotational flow of the AR's leading sunspot, which makes the core field lines to form a coherent S shape consistent with the sigmoid structure as seen in the SDO/AIA images. The total magnetic energy obtained in the simulation matches closely the accumulated magnetic energy as calculated directly from the original vector magnetogram with the DAVE4VM derived flow field. Such a data-driven model will be used to study how the coronal field, as driven by the slow photospheric motions, reaches a unstable state and runs into eruptions. △ Less

Submitted 15 April, 2021; originally announced April 2021.

Comments: 11 pages, 8 figures, accepted by Frontiers in Physics

Strangeness and $Δ$ resonance in compact stars with relativistic-mean-field models

Authors: Ting-Ting Sun, Shi-Sheng Zhang, Qiu-Lan Zhang, Cheng-Jun Xia

Abstract: We explore the effects of strangeness and $Δ$ resonance in baryonic matter and compact stars within the relativistic-mean-field (RMF) models. The covariant density functional PKDD is adopted for $N$-$N$ interaction, parameters fixed based on finite hypernuclei and neutron stars are taken for the hyperon-meson couplings, and the universal baryon-meson coupling scheme is adopted for the $Δ$-meson co… ▽ More We explore the effects of strangeness and $Δ$ resonance in baryonic matter and compact stars within the relativistic-mean-field (RMF) models. The covariant density functional PKDD is adopted for $N$-$N$ interaction, parameters fixed based on finite hypernuclei and neutron stars are taken for the hyperon-meson couplings, and the universal baryon-meson coupling scheme is adopted for the $Δ$-meson couplings. In light of the recent observations of GW170817 with the dimensionless combined tidal deformability $197 \leq \barΛ\leq 720$, we find it is essential to include the $Δ$ resonances in compact stars, and small $Δ$-$ρ$ coupling $g_{ρΔ}$ is favored if the mass $2.27{}_{-0.15}^{+0.17}\ M_\odot$ of PSR J2215+5135 is confirmed. △ Less

Submitted 5 January, 2019; v1 submitted 7 August, 2018; originally announced August 2018.

Journal ref: Phys. Rev. D 99, 023004 (2019)

Follow up of GW170817 and its electromagnetic counterpart by Australian-led observing programs

Authors: I. Andreoni, K. Ackley, J. Cooke, A. Acharyya, J. R. Allison, G. E. Anderson, M. C. B. Ashley, D. Baade, M. Bailes, K. Bannister, A. Beardsley, M. S. Bessell, F. Bian, P. A. Bland, M. Boer, T. Booler, A. Brandeker, I. S. Brown, D. Buckley, S. -W. Chang, D. M. Coward, S. Crawford, H. Crisp, B. Crosse, A. Cucchiara , et al. (100 additional authors not shown)

Abstract: The discovery of the first electromagnetic counterpart to a gravitational wave signal has generated follow-up observations by over 50 facilities world-wide, ushering in the new era of multi-messenger astronomy. In this paper, we present follow-up observations of the gravitational wave event GW170817 and its electromagnetic counterpart SSS17a/DLT17ck (IAU label AT2017gfo) by 14 Australian telescope… ▽ More The discovery of the first electromagnetic counterpart to a gravitational wave signal has generated follow-up observations by over 50 facilities world-wide, ushering in the new era of multi-messenger astronomy. In this paper, we present follow-up observations of the gravitational wave event GW170817 and its electromagnetic counterpart SSS17a/DLT17ck (IAU label AT2017gfo) by 14 Australian telescopes and partner observatories as part of Australian-based and Australian-led research programs. We report early- to late-time multi-wavelength observations, including optical imaging and spectroscopy, mid-infrared imaging, radio imaging, and searches for fast radio bursts. Our optical spectra reveal that the transient source afterglow cooled from approximately 6400K to 2100K over a 7-day period and produced no significant optical emission lines. The spectral profiles, cooling rate, and photometric light curves are consistent with the expected outburst and subsequent processes of a binary neutron star merger. Star formation in the host galaxy probably ceased at least a Gyr ago, although there is evidence for a galaxy merger. Binary pulsars with short (100 Myr) decay times are therefore unlikely progenitors, but pulsars like PSR B1534+12 with its 2.7 Gyr coalescence time could produce such a merger. The displacement (about 2.2 kpc) of the binary star system from the centre of the main galaxy is not unusual for stars in the host galaxy or stars originating in the merging galaxy, and therefore any constraints on the kick velocity imparted to the progenitor are poor. △ Less

Submitted 16 October, 2017; originally announced October 2017.

Comments: 26 pages, 9 figures, 15 tables

Optical Observations of LIGO Source GW 170817 by the Antarctic Survey Telescopes at Dome A, Antarctica

Authors: Lei Hu, Xuefeng Wu, I. Andreoni, Michael C. B. Ashley, J. Cooke, Xiangqun Cui, Fujia Du, Zigao Dai, Bozhong Gu, Yi Hu, Haiping Lu, Xiaoyan Li, Zhengyang Li, Ensi Liang, Liangduan Liu, Bin Ma, Zhaohui Shang, Tianrui Sun, N. B. Suntzeff, Charling Tao, Syed A. Uddin, Lifan Wang, Xiaofeng Wang, Haikun Wen, Di Xiao , et al. (8 additional authors not shown)

Abstract: The LIGO detection of gravitational waves (GW) from merging black holes in 2015 marked the beginning of a new era in observational astronomy. The detection of an electromagnetic signal from a GW source is the critical next step to explore in detail the physics involved. The Antarctic Survey Telescopes (AST3), located at Dome A, Antarctica, is uniquely situated for rapid response time-domain astron… ▽ More The LIGO detection of gravitational waves (GW) from merging black holes in 2015 marked the beginning of a new era in observational astronomy. The detection of an electromagnetic signal from a GW source is the critical next step to explore in detail the physics involved. The Antarctic Survey Telescopes (AST3), located at Dome A, Antarctica, is uniquely situated for rapid response time-domain astronomy with its continuous night-time coverage during the austral winter. We report optical observations of the GW source (GW~170817) in the nearby galaxy NGC 4993 using AST3. The data show a rapidly fading transient at around 1 day after the GW trigger, with the $i$-band magnitude declining from $17.23\pm0.13$ magnitude to $17.72\pm0.09$ magnitude in $\sim 1.8$ hour. The brightness and time evolution of the optical transient associated with GW~170817 are broadly consistent with the predictions of models involving merging binary neutron stars. We infer from our data that the merging process ejected about $\sim 10^{-2}$ solar mass of radioactive material at a speed of up to $30\%$ the speed of light. △ Less

Submitted 17 October, 2017; v1 submitted 16 October, 2017; originally announced October 2017.

Comments: 10 pages, 4 Figures

Autonomous Orbit Determination Using Epoch-Differenced Gravity Gradients and Starlight Refraction

Authors: Pei Chen, Tengda Sun, Xiucong Sun

Abstract: Autonomous orbit determination via integration of epoch-differenced gravity gradients and starlight refraction is proposed in this paper for low-Earth-orbiting satellites operating in GPS-denied environments. The starlight refrac-tion can compensate for the significant along-track position error using solely gravity gradients and benefit from the integration in view of accuracy improvement in radi… ▽ More Autonomous orbit determination via integration of epoch-differenced gravity gradients and starlight refraction is proposed in this paper for low-Earth-orbiting satellites operating in GPS-denied environments. The starlight refrac-tion can compensate for the significant along-track position error using solely gravity gradients and benefit from the integration in view of accuracy improvement in radial and cross-track position estimates. The between-epoch dif-ferencing of gravity gradients is employed to eliminate slowly varying measurement biases and noises near the orbit revolution frequency. The refraction angle is directly used as measurement and its Jacobian matrix is derived from an implicit observation equation. An information fusion filter based on sequential extended Kalman filter is devel-oped for the orbit determination. Truth-model simulations are used to test the performance of the algorithm and the effects of differencing intervals and orbital heights are analyzed. A semi-simulation study using actual gravity gra-dient data from the Gravity field and steady-state Ocean Circulation Explorer (GOCE) combined with simulated starlight refraction measurements is further conducted and a three-dimensional position accuracy of better than 100 m is achieved. △ Less

Submitted 7 February, 2017; originally announced February 2017.

Comments: 24 pages, 7 figures, initially accepted in Chinese Journal of Aeronautics

Energy dissipation processes in solar wind turbulence

Authors: Y. Wang, F. S. Wei, X. S. Feng, X. J. Xu, J. Zhang, T. R. Sun, P. B. Zuo

Abstract: Turbulence is a chaotic flow regime filled by irregular flows. The dissipation of turbulence is a fundamental problem in the realm of physics. Theoretically, dissipation cannot be ultimately achieved without collisions, and so how turbulent kinetic energy is dissipated in the nearly collisionless solar wind is a challenging problem. Wave particle interactions and magnetic reconnection are two poss… ▽ More Turbulence is a chaotic flow regime filled by irregular flows. The dissipation of turbulence is a fundamental problem in the realm of physics. Theoretically, dissipation cannot be ultimately achieved without collisions, and so how turbulent kinetic energy is dissipated in the nearly collisionless solar wind is a challenging problem. Wave particle interactions and magnetic reconnection are two possible dissipation mechanisms, but which mechanism dominates is still a controversial topic. Here we analyze the dissipation region scaling around a solar wind magnetic reconnection region. We find that the magnetic reconnection region shows a unique multifractal scaling in the dissipation range, while the ambient solar wind turbulence reveals a monofractal dissipation process for most of the time. These results provide the first observational evidences for the intermittent multifractal dissipation region scaling around a magnetic reconnection site, and they also have significant implications for the fundamental energy dissipation process. △ Less

Submitted 31 December, 2015; v1 submitted 11 December, 2015; originally announced December 2015.

Comments: 6 pages, 5 figures, published in Astrophysical Journal Supplement Series

Energetic Electrons Associated with Magnetic Reconnection in the Magnetic Cloud Boundary Layer

Authors: Y. Wang, F. S. Wei, X. S. Feng, S. H. Zhang, P. B. Zuo, T. R. Sun

Abstract: Here is reported in situ observation of energetic electrons (~100-500 keV) associated with magnetic reconnection in the solar wind by the ACE and Wind spacecraft. The properties of this magnetic cloud driving reconnection and the associated energetic electron acceleration problem are discussed. Further analyses indicate that the electric field acceleration and Fermi type mechanism are two fundamen… ▽ More Here is reported in situ observation of energetic electrons (~100-500 keV) associated with magnetic reconnection in the solar wind by the ACE and Wind spacecraft. The properties of this magnetic cloud driving reconnection and the associated energetic electron acceleration problem are discussed. Further analyses indicate that the electric field acceleration and Fermi type mechanism are two fundamental elements in the electron acceleration processes and the trapping effect of the specific magnetic field configuration maintains the acceleration status that increases the totally gained energy. △ Less

Submitted 24 June, 2012; originally announced June 2012.

Comments: First observational evidence of energetic electrons associated with magnetic reconnection in the solar wind; Physical Review Letters(2010)