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

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 ${\bm~{Einstein~~Probe}}$

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Analysis of interval constants in calendars affiliated with the Shoushili

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Research in astronomy and Astrophysics 2014年第4期14卷 485-496页

作者： Byeong-Hee Mihn Ki-Won Lee Young Sook Ahn advanced astronomy and space science division Korea Astronomy and Space Science Institute Department of astronomy and space science Chungbuk National University Institute of Liberal Education Catholic University of Daegu

We study interval constants that are related to motions of the Sun and Moon, i.e., the Qi, Intercalation, Revolution and Crossing interval, in calendars affiliated with the Shoushi calendar （Shoushili）, such as Datongli and Chiljeongsannaepyeon. It is known that these interval constants were newly introduced in the Shoushili calendar and revised afterward, except for the Qi interval constant, and the revised values were adopted in later calendars affiliated with the Shoushili. We first investigate the accu- racy of these interval constants and then the accuracy of calendars affiliated with the Shoushili in terms of these constants by comparing times for the new moon and the maximum solar eclipse calculated by each calendar with modem methods of calcula- tion. During our study, we found that the Qi and Intercalation interval constants used in the early Shoushili were well determined, whereas the Revolution and Crossing interval constants were relatively poorly measured. We also found that the interval constants used by the early Shoushili were better than those of the later one, and hence better than those of Datongli and Chiljeongsannaepyeon. On the other hand, we found that the early Shoushili is, in general, a worse calendar than Datongli for use in China but a better one than Chiljeongsannaepyeon for use in Korea in terms of times for the new moon and when a solar eclipse occurs, at least for the period 1281 - 1644. Finally, we verified that the times for sunrise and sunset in the Shoushili-Li-Cheng and Mingshi are those at Beijing and Nanjing, respectively.

关键词： history and philosophy of astronomy: general -- celestial mechanics --ephemerides

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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

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Disruption of Charged Dust Grains in Cometary Plasma Environments

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Chinese Physics Letters 1998年第2期15卷 155-156页

作者： SHI Zhi-dong LI Zhong-yuan CHEN Yao Department of Earth and space science University of Science and Technology of ChinaHefei 230026 advanced Center for Earth science and astronomy Third World Academy of Science

The equilibrium potential and dust fragmentation criterion of fluffy dust grains in plasma are calculated for comet P/*** is found that the dust grain acquires its largest negative potential and disruptive probability... 详细信息

关键词： change. comet criterion

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Contribution from normal and starburst galaxies to the extragalactic gamma-ray background (EGRB)

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Chinese Journal of astronomy and Astrophysics 2009年第5期9卷 509-519页

作者： Debbijoy Bhattacharya Parameswaran Sreekumar Department of Physics Indian Institute of Science space astronomy & Instrumentation division ISRO Satellite Centre

The extragalactic diffuse emission at γ-ray energies has interesting cosmological implications since these photons suffer little or no attenuation during their propagation from the site of origin. The emission could originate from either truly diffuse processes or from unresolved point sources such as AGNs, normal galaxies and starburst galaxies. Here, we examine the unresolved point source origin of the extragalactic γ-ray background emission from normal galaxies and starburst galaxies. γ-ray emission from normal galaxies is primarily coming from cosmic-ray interactions with interstellar matter and radiation （-90%） along with a small contribution from discrete point sources （-10%）. Starburst galaxies are expected to have enhanced supernovae activity which leads to higher cosmic-ray densities, making starburst galaxies sufficiently luminous atγ-ray energies to be detected by the current γ-ray mission （Fermi Gamma-ray space Telescope）.

关键词： galaxy general -- galaxies luminosity function -- galaxies starburst -- gamma-rays observations

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Photometric study of eclipsing binaries in the Large Magellanic Cloud--I.W UMa type binaries in the Large Magellanic Cloud

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Research in astronomy and Astrophysics 2011年第2期11卷 175-180页

作者： Devarapalli Shanti Priya Kandulapati Sriram Pasagada Vivekananda Rao Department of astronomy Osmania University Korea astronomy and space science Institute

Eclipsing binaries are among the most important sources of information on stellar parameters like radii,masses,luminosities,*** present the analysis of six W UMa systems discovered in the Large Magellanic Cloud using ... 详细信息

关键词： binaries: eclipsing -- binaries: close

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CCD photometry of W UMa-type contact binaries in the old open cluster Berkeley 39

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Research in astronomy and Astrophysics 2011年第12期11卷 1469-1481页

作者： Yellapragada Ravi Kiron Kandulapati Sriram Pasagada Vivekananda Rao Department of astronomy Osmania University Korea astronomy and space science Institute

We present the combined BVI multicolor photometric solutions of seven EW variables in the old open cluster Berkeley 39. The observations were carried out in the B and V passbands from the 2 m telescope at the IUCAA-Girawali Observatory in India. The analysis is done using the 2003 version of the Wilson-Devinney code and the fitted light curves are presented. The light curves appear to be symmetric in all the passbands. The photometric solutions suggest that the variables are W-type systems. The new ephemeris indicates that the orbital periods of the studied variables have not changed during the timespan of observations. Revised orbital period, absolute mass, radius and luminosity of the respective variables are presented. The absolute physical parameters of the variables follow the trend of field EW stars. Comparing the results obtained with the other theoretical works, we suggest that there is an excess loss of mass and angular momentum in these systems which may be due to their short period and relatively young age, possibly due to the presence of a third component or the initial detached period being less than 2 d.

关键词： binaries -- eclipsing: contact: W UMa stars

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Photometric study of an eclipsing binary in Praesepe

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Research in astronomy and Astrophysics 2013年第4期13卷 465-470页

作者： Devarapalli Shanti Priya Kandulapati Sriram Pasagada Vivekananda Rao Department of astronomy Osmania University Korea astronomy and space science Institute

We present CCD photometric observations of an eclipsing binary in the direction of the open cluster Praesepe using the 2 m telescope at IUCAA Girawali Observatory, India. Though the system was classified as an eclipsing binary by Pepper et al., detailed investigations have been lacking. The photometric solutions using the Wilson-Devinney code suggest that it is a W-type W UMa system and, interestingly, the system parameters are similar to another contact binary system SW Lac.

关键词： binaries: eclipsing - binaries: close -open clusters: Praesepe

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The physical properties of galaxies with unusually high gas-phase metallicity

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Research in astronomy and Astrophysics 2020年第2期20卷 53-66页

作者： Yong-Yun Chen Qiu-Sheng Gu Xue Ge School of astronomy and space science Nanjing University

We use 1221 galaxies with unusually high gas-phase metallicity to study their physical *** scope of redshift is 0.02 < z < 0.25 for these galaxies with unusually high gas-phase *** goal is to understand the physical origins of the high gas-phase *** address this study,we select a control sample matching similar redshift and stellar *** main results are as follows.(i) Compared with the control sample,the high-metallicity sample shows lower ionization parameter,higher electron density and more dust content.(ii) We also find that the high-metallicity sample has older stellar age and higher [Mgb/] ratio,which indicates that the high-metallicity sample has shorter timescale of star formation.(iii) According to the plane of Hδ_A vs.D_n4000,we can see that the control sample has higher HδAand lower D_n4000 than the high-metallicity sample,which may imply that the control sample experiences recent star formation.(iv) There is a significant difference in gas distribution between the highmetallicity and control *** high-metallicity sample has lower gas fraction than control sample,which indicates that galaxies have high gas-phase metallicity probably due to their low HI gas fraction.(v) There is no significant difference between the high-metallicity and control samples in environment,which may suggest that the environment has no effect on gas-phase metallicity.

关键词： galaxies:evolution galaxies:formation galaxies:abundance galaxies:ISM galaxies:star formation

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The symmetry energy and incompressibility constrained by the observations of glitching pulsars

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Research in astronomy and Astrophysics 2019年第5期19卷 101-112页

作者： Yan Yan School of astronomy and space science Nanjing University

We investigate the masses of glitching pulsars in order to constrain their equation of state(EOS). The observations of glitches(sudden jumps in rotational frequency) may provide information on the interior physics of neutron stars. With the assumption that glitches are triggered by superfluid neutrons, the masses of glitching neutron stars can be estimated using observations of maximum *** with the observations of thermal emission from glitching pulsars Vela and J1709–4429, the slope of symmetry energy and incompressibility of nuclear matter at saturation density can be *** slope of symmetry energy L should be larger than 67 MeV while the lower limit of incompressibility for symmetric nuclear matter K_0 is 215 MeV. We also obtain a relationship between L and K_0:6.173 MeV + 0.283 K_0≤ L ≤ 7.729 MeV + 0.291 K_0. The restricted EOSs are consistent with the observations of 2-solar-mass neutron stars and gravitational waves from a binary neutron star inspiral.

关键词： neutron stars:glitch neutron stars:cooling neutron stars:tidal deformability nuclear physics:symmetry energy

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