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Einstein Probe discovery of EP240408a: A peculiar X-ray transient with an intermediate timescale

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Science China(Physics,Mechanics & Astronomy) 2025年第1期Mechanics & Astronomy) .卷 222-240页

作者： Wenda Zhang Weimin Yuan Zhixing Ling Yong Chen Nanda Rea Arne Rau Zhiming Cai Huaqing Cheng Francesco Coti Zelati Lixin Dai Jingwei Hu Shumei Jia Chichuan Jin Dongyue Li Paul O’Brien Rongfeng Shen Xinwen Shu Shengli Sun Xiaojin Sun Xiaofeng Wang Lei Yang Bing Zhang Chen Zhang Shuang-Nan Zhang Yonghe Zhang Jie An David Buckley Alexis Coleiro Bertrand Cordier Liming Dou Rob Eyles-Ferris Zhou Fan Hua Feng Shaoyu Fu Johan P.U.Fynbo Lluis Galbany Saurabh W.Jha Shuaiqing Jiang Albert Kong Erik Kuulkers Weihua Lei Wenxiong Li Bifang Liu Mingjun Liu Xing Liu Yuan Liu Zhu Liu Chandreyee Maitra Alessio Marino Itumeleng Monageng Kirpal Nandra Jeremy Sanders Roberto Soria Lian Tao Junfeng Wang Song Wang Tinggui Wang Zhongxiang Wang Qingwen Wu Xuefeng Wu Dong Xu Yanjun Xu Suijian Xue Yongquan Xue Zijian Zhang Zipei Zhu Hu Zou Congying Bao Fansheng Chen Houlei Chen Tianxiang Chen Wei Chen Yehai Chen Yifan Chen Chenzhou Cui Weiwei Cui Yanfeng Dai Dongwei Fan Ju Guan Dawei Han Dongjie Hou Haibo Hu Maohai Huang Jia Huo Zhenqing Jia Bowen Jiang Ge Jin Chengkui Li Junfei Li Longhui Li Maoshun Li Wei Li Zhengda Li Tianying Lian Congzhan Liu Heyang Liu Huaqiu Liu Fangjun Lu Laidan Luo Jia Ma Xuan Mao Haiwu Pan Xin Pan Liming Song Hui Sun Yunyin Tan Qingjun Tang Yihan Tao Hao Wang Juan Wang Lei Wang Wenxin Wang Yilong Wang Yusa Wang Qinyu Wu Haitao Xu Jingjing Xu Xinpeng Xu Yunfei Xu Zhao Xu Changbin Xue Yulong Xue Ailiang Yan Haonan Yang Xiongtao Yang Yanji Yang Juan Zhang Mo Zhang Wenjie Zhang Zhen Zhang Zhen Zhang Ziliang Zhang Donghua Zhao Haisheng Zhao Xiaofan Zhao Zijian Zhao Hongyan Zhou Yilin Zhou Yuxuan Zhu Zhencai Zhu National Astronomical Observatories Chinese Academy of Sciences School of Astronomy and Space Sciences university of Chinese Academy of Sciences Key Laboratory of Particle Astrophysics institute of High Energy Physics Chinese Academy of Sciences institute of Space Sciences (ICE) CSIC Institut d’Estudis Espacials de Catalunya (IEEC) Max Planck institute for Extraterrestrial Physics Innovation Academy for Microsatellites Chinese Academy of Sciences Department of Physics university of Hong Kong School of Physics and Astronomy university of Leicester School of Physics and Astronomy Sun Yat-sen university Department of Physics Anhui Normal university Shanghai institute of Technical Physics Chinese Academy of Sciences Physics Department Tsinghua university Nevada Center for Astrophysics university of Nevada Las Vegas Department of Physics and Astronomy university of Nevada Las Vegas South African Astronomical observatory Department of Astronomy university of Cape Town Department of Physics university of the Free State Université Paris Cité CNRS Astroparticule et Cosmologie Université Paris Cité CEA Paris-Saclay IRFU/DAp-AIM Department of Astronomy Guangzhou university Cosmic Dawn Center (DAWN) Niels Bohr institute university of Copenhagen Department of Physics and Astronomy Rutgers the State university of New Jersey institute for Cosmic Ray Research The university of Tokyo ESA/ESTEC Department of Astronomy School of Physics Huazhong university of Science and Technology INAF-Osservatorio Astrofisico di Torino Sydney institute for Astronomy School of Physics The university of Sydney Department of Astronomy Xiamen university institute for Frontiers in Astronomy and Astrophysics Beijing Normal university Department of Astronomy university of Science and Technology School of Astronomy and Space Sciences university of Science and Technology of China institute of Deep Space Sciences Deep Space Exploration Laboratory Department of Astronomy School of Physics and Astronomy Yunnan university Shanghai Astronomical observatory Chi

We report the discovery of a peculiar X-ray transient,EP240408a,by Einstein Probe （EP） and follow-up studies made with EP,Swift,NICER,GROND,ATCA and other ground-based multiwavelength *** new transient was first detected with Wide-field X-ray Telescope （WXT） on board EP on April 8th,2024,manifested in an intense yet brief X-ray flare lasting for *** flare reached a peak flux of 3.9×10-9erg cm-2s-1in 0.5-4 ke V,～300 times brighter than the underlying X-ray emission detected throughout the *** and more precise follow-up observations by EP/FXT,Swift and NICER confirmed the finding of this new *** X-ray spectrum is non-thermal in 0.5-10 ke V,with a power-law photon index varying *** X-ray light curve shows a plateau lasting for ～4 d,followed by a steep decay till becoming undetectable ～10 d after the initial *** on its temporal property and constraints from previous EP observations,an unusual timescale in the range of 7-23 d is found for EP240408a,which is intermediate between the commonly found fast and long-term *** counterparts have been found in optical and near-infrared,with the earliest observation at 17 h after the initial X-ray detection,suggestive of intrinsically weak emission in these *** demonstrate that the remarkable properties of EP240408a are inconsistent with any of the transient types known so far,by comparison with,in particular,jetted tidal disruption events,gamma-ray bursts,X-ray binaries and fast blue optical *** nature of EP240408a thus remains an *** suggest that EP240408a may represent a new type of transients with intermediate timescales of the order of～10 *** detection and follow-ups of more of such objects are essential for revealing their origin.

关键词： X-ray transients ${\bm~{Einstein~~Probe}}$

Wave effect of gravitational waves intersected with a microlens field Ⅱ:An adaptive hierarchical tree algorithm and population study

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Science China(Physics,Mechanics & Astronomy) 2025年第1期Mechanics & Astronomy) .卷 241-254页

作者： Xikai Shan Guoliang Li Xuechun Chen Wen Zhao Bin Hu Shude Mao Department of Astronomy Tsinghua University Purple Mountain observatory Chinese Academy of Sciences institute for Frontier in Astronomy and Astrophysics Beijing Normal University School of Physics and Astronomy Beijing Normal University School of Astronomy and Space Science University of Science and Technology of China CAS Key Laboratory for Researches in Galaxies and Cosmology Department of Astronomy University of Science and Technology of ChinaChinese Academy of Sciences

The gravitational lensing wave effect generated by a microlensing field embedded in a lens galaxy is an inevitable phenomenon in strong lensed gravitational waves （SLGWs）.This effect presents both challenges and opportunities for the detection and application of ***,investigating this wave effect requires computing a complete diffraction integral over each microlens in the *** is extremely time-consuming due to the large number of microlenses （10～3-10～6）.Therefore,simply adding all the microlenses is ***,the complexity of the time delay surface makes the lens plane resolution a crucial factor in controlling numerical *** this paper,we propose a trapezoid approximation-based adaptive hierarchical tree algorithm to meet the challenges of calculation speed and *** find that this algorithm accelerates the calculation by four orders of magnitude compared to the simple adding method and is one order of magnitude faster than the fixed hierarchical tree algorithm proposed for electromagnetic *** importantly,our algorithm ensures controllable numerical errors,increasing confidence in the *** with our previous work （***.66,239511,2023）,this paper addresses all numerical issues,including integral convergence,precision,and computational time1).Finally,we conducted a population study on the microlensing wave effect of SLGWs using this algorithm and found that the microlensing wave effect cannot be ignored,especially for Type II SLGWs （from saddle position of the time delay surface） due to their intrinsic geometric structures and their typical intersection with a denser microlensing ***,more than 33%（11%） of SLGWs have a mismatch larger than 1%（3%） compared to the unlensed ***,we found that the mismatch between signal pairs in a doubly imaged GW is generally larger than 10-3,and 61%（25%） of signal pairs have a mismatch larger than 1%（3%）.Therefo

关键词： gravitational lensing diffractional integral algorithm gravitational wave

GSC 4560–02157: a new long-period eclipsing cataclysmic variable star

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Research in Astronomy and Astrophysics 2015年第7期15卷 1005-1011页

作者： Anton V.Khruslov Anatoly V.Kusakin Elena A.Barsukova Vitaly P.Goranskij Azamat F.Valeev Nikolay N.Samus institute of Astronomy Russian Academy of Sciences Fesenkov astrophysical institute Special astrophysical observatory Russian Academy of Sciences Sternberg Astronomical institute Lomonosov Moscow State University

We study the newly discovered variable star GSC 4560-02157. CCD photometry was performed in 2013-2014 at the Tien Shan Astronomical observatory,and a spectrum was obtained with the 6-m telescope of the Special astrophysical observatory in June, 2014. GSC 4560-02157 is demonstrated to be an eclipsing variable star（P = 0.265359d）. All its flat-bottom primary minima are approximately at the same brightness level, but the star＇s out-of-eclipse brightness and brightness at secondary minima vary considerably（by up to 0.6m） from cycle to cycle. Moreover,there are short-term（time scale of 0.03-0.04 days） small-amplitude brightness variations out of eclipse. This behavior suggests a cataclysmic nature for the star, which is confirmed with a spectrum taken on 2014 June 5. The spectrum shows numerous emissions of the hydrogen Balmer series, He Ⅰ and He Ⅱ.

关键词： stars: dwarf novae -- binaries: eclipsing -- stars: individual: GSC 4560-02157

Debris disks: seeing dust, thinking of planetesimals and planets

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Research in Astronomy and Astrophysics 2010年第5期10卷 383-414页

作者： Alexander V. Krivov astrophysical institute and university observatory Friedrich Schiller University JenaSchillergchen 2-3 07745 Jena Germany

Debris disks are optically thin, almost gas-free dusty disks observed arounda significant fraction of main-sequence stars older than about 10 Myr. Since the circumstellar dust is short-lived, the very existence of these disks is considered as evi-dence that dust-producing planetesimals are still present in mature systems, in whichplanets have formed – or failed to form – a long time ago. It is inferred that theseplanetesimals orbit their host stars at asteroid to Kuiper-belt distances and continuallysupply fresh dust through mutual collisions. This review outlines observational techniques and results on debris disks, summarizes their essential physics and theoreticalmodels, and then places them into the general context of planetary systems, uncovering interrelations between the disks, dust parent bodies, and planets. It is shownthat debris disks can serve as tracers of planetesimals and planets and shed light onthe planetesimal and planet formation processes that operated in these systems in thepast.

关键词： planetary systems: formation — circumstellar matter

The detection, extraction and parameter estimation of extreme-mass-ratio inspirals with deep learning

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Science China(Physics,Mechanics & Astronomy) 2025年第1期Mechanics & Astronomy) .卷 86-96页

作者： Qianyun Yun Wen-Biao Han Yi-Yang Guo He Wang Minghui Du Hangzhou institute for Advanced Study University of Chinese Academy of Sciences Shanghai Astronomical observatory Chinese Academy of Sciences School of Physics and Astronomy Shanghai Jiao Tong University School of Astronomy and Space Science University of Chinese Academy of Sciences Taiji Laboratory for Gravitational Wave Universe (Beijing/Hangzhou) University of Chinese Academy of Sciences Lanzhou Center for Theoretical Physics Key Laboratory of Theoretical Physics of Gansu Province Key Laboratory of Quantum Theory and Applications of MoE Lanzhou University institute of Theoretical Physics & Research Center of Gravitation Lanzhou University International Centre for Theoretical Physics Asia-Pacific (ICTP-AP) University of Chinese Academy of Sciences (UCAS) Center for Gravitational Wave Experiment National Microgravity Laboratory Institute of Mechanics Chinese Academy of Sciences

One of the primary goals of space-borne gravitational wave detectors is to detect and analyze extreme-mass-ratio inspirals(EMRIs). This task is particularly challenging because EMRI signals are complex, lengthy, and faint. In this work, we introduce a2-layer convolutional neural network(CNN) approach to detect EMRI signals for space-borne detectors, achieving a true positive rate(TPR) of 96.9% at a 1% false positive rate(FPR) for signal-to-noise ratio(SNR) from 50 to 100. Especially, the key intrinsic parameters of EMRIs such as the mass, spin of the supermassive black hole(SMBH) and the initial eccentricity of the orbit can also be inferred directly by employing a neural network. The mass and spin of the SMBH can be determined at 99% and 92% respectively. This will greatly reduce the parameter spaces and computing cost for the following Bayesian parameter *** model also has a low dependency on the accuracy of the waveform model. This study underscores the potential of deep learning methods in EMRI data analysis, enabling the rapid detection of EMRI signals and efficient parameter estimation.

关键词： gravitational wave EMRIs deep-learing

Variability of emission lines in the optical spectra of the Herbig Be binary system HD 200775

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Research in Astronomy and Astrophysics 2019年第3期19卷 31-34页

作者： Anastasia P.Bisyarina ANDrey M.Sobolev Stanislav Yu.Gorda Anatoly S.Miroshnichenko Astronomical observatory of the Ural Federal university Department of Physics and Astronomy University of North Carolina at Greensboro Main (Pulkovo) Astronomical observatory of the Russian Academy of Sciences Fesenkov astrophysical institute

In our previous papers we have improved the value of the orbital period of the binary Herbig Be star HD 200775 and showed that the [O I] and Si II 6347 and 6371 ?A emission lines displayed variations which correlate with the orbital period. In this paper we provide evidences that other broad emission lines of metals in the spectra of HD 200775 also exhibit variability, which is probably related to the orbital cycle of the binary. Analysis was performed based on the high-resolution spectral data collected over a time span of 6 years at the Kourovka Astronomical observatory of the Ural Federal university(Russia) and the Three College observatory of the university of North Carolina at Greensboro(USA) as well as archival spectral data compiled since 1994. We report new data points in the radial velocity curve of the He I 5876 ?A line near the extremal values of the radial velocity.

关键词： techniques spectroscopic-stars variables T Tauri,Herbig Ae/Be-stars individual HD 200775

Analysis of X-Ray Emission from OB Stars. IV. About X-Ray Emission from Inhomogeneous Winds of OB Stars

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Research in Astronomy and Astrophysics 2023年第10期23卷 387-405页

作者： Elizaveta Ryspaeva Alexander Kholtygin Crimean astrophysical observatory NauchnyCrimeaRussia Saint-Petersburg State university Saint-PetersburgRussia

We study the origin of X-ray emission from OB stars due to collisions of stellar winds and/or inhomogeneities in the winds. The low-resolution X-ray spectra of a big sample of OB stars were fitted by both the stationary APEC/MEKAL models and by this model with an additional PSHOCK component describing the nonstationary X-ray emission. These spectra were also described by two-temperature PSHOCK models. More than ~50% of considered spectra can be described by the above-mentioned model combinations including the PSHOCK model and the quality of the fits appears to be better for O stars. The plasma temperature of the PSHOCK component is about 1–5 keV with the ionization timescale τ_(u)~ 10^(8)–10^(13)s cm^(-3). The temperature of the PSHOCK component increases with the momentum and kinetic energy of the stellar wind by a power law with an index ~0.12–*** dependencies were not revealed through modeling by the stationary APEC/MEKAL models only. At the same time the X-ray luminosity of OB stars depends on momentum and kinetic energy of their winds similarly either for stationary or for nonstationary models. We conclude that many O stars and some B stars can be sources of the nonstationary X-rays formed in their inhomogeneous stellar wind.

关键词： stars:early-type stars:statistics X-rays:stars

Analysis of the X-ray emission of OB stars II: B stars

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Research in Astronomy and Astrophysics 2019年第8期19卷 143-150页

作者： Elizaveta Ryspaeva Alexander Kholtygin Crimean astrophysical observatory NauchnyCrimeaRussia Saint-Petersburg State university Saint-PetersburgRussia institute of Astronomy Russian Academy of SciencesRussia

This paper is the second part of an investigation into the mechanism for the origin of X-rays in early-type stars. Archival X-ray observations of 25 B stars, obtained by the XMM-Newton satellite, are analysed. We check two hypotheses on the origin of X-ray emission: the Magnetically Confined Wind Shock Model(MCWS) and Pollock’s paradigm. For all studied stars, the mean ratio of the half widths at half maximum to the terminal velocities appears to be R ≈ 0.15-0.20 in contradiction to Pollock’s hypothesis that R ≈ 0.5. We checked three possible consequences of the MCWS model: correlations between the hardness of the X-ray spectra for B stars and terminal wind velocities, mass loss rates and magnetic *** was shown that such correlations are marginal or even absent both for magnetic and non-magnetic B stars.

关键词： stars:early-type stars:spectra:X-ray

Spectral study of V565 Mon: probable FU Ori-like or chemically peculiar star

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Research in Astronomy and Astrophysics 2021年第3期21卷 128-132页

作者： Hasmik Andreasyan Byurakan astrophysical observatory NAS RAByurakanAragatzotn Prov.0213Armenia

We present a detailed spectroscopic study of pre-main sequence star V565 Mon,which is the illuminating star of the Parsamian 17 cometary *** were performed with the 2.6 m telescope in Byurakan astrophysical observatory on 2018 February *** velocities and equivalent widths of the most prominent lines of V565 Mon are *** build the spectral energy distribution and estimate the main parameters of the star,for example the obtained bolometric luminosity of V565 Mon is L_(V565)≈130 L_(⊙).Considering all features of V565 Mon,we come to the conclusion that this young intermediate-mass star belongs to some intermediate class between T Tau and HAeBe *** unusual for a young star is the presence of strong absorption BaⅡlines in the *** explanations on this issue are ***,we think that V565 Mon is a unique example,which can help to understand some open questions involved in the problem of nucleosynthesis in young stars.

关键词： stars:pre-main sequence stars:variables:T Tauri Herbig Ae/Be stars:individual:V565 Mon