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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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Structure and Inclination Angle of the Spiral Galaxy M31

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Chinese Physics Letters 2001年第10期18卷 1420-1422页

作者： MA Jun National Astronomical Observatories Chinese Academy of SciencesBeijing 100012 joint laboratory of optical astronomy Chinese Academy of SciencesBeijing 100012

The mathematical form, the symmetry of the spiral structure, and the projection of the galactic disc on the image of the spiral galaxy M31 have been directly studied. It is found that M31 has two symmetric arms, i.e. the pitch angles of the two arms are nearly equal;these are 7.7° and 8.0°, respectively. Using the method proposed in this letter, the inclination angle of the galactic disc ofM31 is also obtained, which is 77.5° and is in good agreement with previously published results.

关键词： M31 galactic galaxy

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Metallicity and star formation activities of the interacting system Arp 86 from observations with MOS on the Xinglong 2.16m telescope

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Research in astronomy and Astrophysics 2014年第11期14卷 1393-1405页

作者： Zhi-Min Zhou Hong Wu Lei Huang Hong-Bin Li Zhi-Zhong Zhou Jun-Jun Jia Man-I Lam Yi-Nan Zhu Key laboratory of optical astronomy National Astronomical ObservatoriesChinese Academy of Sciences Key laboratory of optical astronomy National Astronomical Observatories Chinese Academy of Sciences

We present an analysis of the metallicity and star formation activities of H II regions in the interacting system Arp 86, based on the first scientific observations using mulri-object spectroscopy with the 2.16 m telescope at the Xinglong Observing Station. We find that the oxygen abundance gradient in Arp 86 is flatter than that in normal disk galaxies, which confirms that gas inflows caused by tidal forces during encounters can flatten the metallicity distributions in galaxies. The companion galaxy NGC 7752 is currently experiencing a galaxy-wide starburst with a higher star for- marion rate surface density than the main galaxy NGC 7753, which can be explained in that the companion galaxy is more susceptible to the effects of interaction than the primary. We also find that the galaxy 2MASX J23470758＋2926531 has similar abun- dance and star formation properties to NGC 7753, and may be a part of the Arp 86 system.

关键词： galaxies abundances -- galaxies evolution -- galaxies interactions --(ISM:) H II regions -- techniques spectroscopic

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Recent study of emission line star 3G71

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Chinese Science Bulletin 1998年第6期43卷 470-473页

作者： HANG Hengrong 1,2 and XIA Jianping+1 1. Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008, China 2. joint laboratory for optical astronomy, Chinese Academy of Sciences, Nanjing 210008, China Purple Mountain Observatory Chinese Academy of Sciences Nanjing China joint laboratory for optical astronomy Chinese Academy of Sciences Nanjing China

New spectral observations of 3G71 are presented. The main features of optical spectra which exhibit a lot of forbidden lines and unusual strong H-Balmer emission lines are discussed. Our data, together with its large IRAS infrared color excess and other characteristics, show evidence that the star may be a Herbig Ae/Be star rather than the optical counterpart of Be/X-ray source of 1H2214+589.

关键词： Be/X-ray binary emission line IRAS identification Herbig Ae/Be star.

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The SAGE photometric survey: technical description

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Research in astronomy and Astrophysics 2018年第12期18卷 29-42页

作者： Jie Zheng Gang Zhao Wei Wang Zhou Fan Ke-Feng Tan Chun Li Fang Zuo Key laboratory of optical astronomy National Astronomical Observatories Chinese Academy of Sciences School of astronomy and Space Science University of Chinese Academy of Sciences Chinese Academy of Sciences South America Center for astronomy China-Chile Joint Center for AstronomyNational Astronomical Observatories Chinese Academy of Sciences

To investigate a huge sample of data related to the Stellar Abundance and Galactic Evolution(SAGE) survey in more detail, we are performing a northern sky photometric survey named SAGES with the SAGE photometric *** system consists of eight filters: Str?mgren-u, SAGE-v, SDSS g, r, i, DDO-51, Hαwideand Hαnarrow, including three Sloan broadband filters, three intermediateband filters, two narrow-band filters and one newly-designed narrow-band *** covers～12 000 square degrees of the northern sky with δ >-5°, excluding the Galactic disk(|b| < 10°) and the sky area 12 h

关键词： methods:observational techniques:photometric surveys astrometry catalogs

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Test area of the SAGE survey

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Research in astronomy and Astrophysics 2019年第1期19卷 29-34页

作者： Jie Zheng Gang Zhao Wei Wang Zhou Fan Ke-Feng Tan Chun Li Fang Zuo Key laboratory of optical astronomy National Astronomical ObservatoriesChinese Academy of Sciences School of astronomy and Space Science University of Chinese Academy of Sciences Chinese Academy of Sciences South America Center for astronomy China-Chile Joint Center for AstronomyNational Astronomical ObservatoriesChinese Academy of Sciences

Sky surveys represent one of the most important efforts to improve developments in astrophysics,especially when using new photometric bands. We are performing the Stellar Abundance and Galactic Evolution(SAGE) survey with a self-designed SAGE photometric system, which is composed of eight photometric bands. The project mainly aims to study the stellar atmospheric parameters of ～0.5 billion stars in ～12 000 deg2 of the northern sky, which mainly focuses on Galactic astronomy, as well as some aspects of extragalactic astronomy. This work introduces the detailed data reduction process of the test field NGC 6791, including the data reduction of single-exposure images and stacked multi-exposure images, and properties of the final catalog.

关键词： methods:observational techniques:photometric surveys astrometry catalogs

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An empirical L-band scintillation model for a mid-latitude station,Weihai, China during the low solar activity period

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Science China(Technological Sciences) 2019年第7期62卷 1182-1190页

作者： PRIYADARSHI Shishir ZHANG Qing-He WANG Yong Shandong Provincial Key laboratory of optical astronomy and Solar-Terrestrial Environment Institute of Space SciencesShandong University

Mid-latitude ionospheric scintillation has been studied in very poor proportion as compared to the equatorial and high latitude ionospheric scintillation. Mid-latitude ionospheric scintillations are often associated with either day time photo-ionization or due to the storm enhanced density. Using the phase screen model and the wave propagation theory in random media, we have identified the orientation of the ionospheric irregularities over Weihai with the local geomagnetic field. Amplitude and phase scintillation data observed using global positioning system(GPS) scintillation receiver deployed at the mid-latitude observation station Weihai, have been used along with K-index derived from the horizontal magnetic field component of the local magnetometer. The proposed model uses the scintillation indices relationship with the local K-index. We identified the scintillation dependence over local K-index during geomagnetic quiet and disturbed condition. This dependence coefficient is used on the real scintillation data for modeling. The presented scintillation model has been validated by comparing it to the real observations. The co-relation coefficient is more than 90% during the disturbed as well as quiet geomagnetic conditions.

关键词： mid-latitude ionosphere scintillation GPS global navigation satellite systems (GNSS)

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Planet host stars in open clusters

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Science China(Physics,Mechanics & astronomy) 2015年第3期58卷 96-101页

作者： YANG XiaoLing CHEN YuQin ZHAO Gang Key laboratory of optical astronomy National Astronomical Observatories Chinese Academy of Sciences University of Chinese Academy of Sciences

We have compiled a list of all planet host star candidates reported in the literature,which are likely to be cluster members,and we checked their memberships by the spatial location,radial velocity,proper motion and photometric *** found that only six stars,BD-13 2130,HD 28305,Kepler-66,Kepler-67,Pr0201 and Pr0211,are planet orbiting stars in open clusters to *** stars,HD 70573 and HD 89744,belong to moving groups and one star,TYC 8975-2606-1,may not be a planet host star,while three stars,HD 16175,HD 46375 and HD 108874 are not members of open *** note that all these six planetary systems in the stellar cluster environment are younger than^1 Gyr,which might indicate that the planetary system in open cluster can not survive for a long time,and we speculate that close stellar encounters between member stars in open cluster can potentially destroy,or at least strongly affect,the presence of planetary systems.

关键词： extrasolar planets planetary survival open cluster

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Anomalous Variation of Beat Frequency in a Dual Frequency He-Ne Laser

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Chinese Physics Letters 2016年第2期33卷 51-54页

作者：刘维新孙明哲 Shandong Provincial Key laboratory of optical astronomy and Solar-Terrestrial Environment Institute of Space SciencesShandong University

The beat frequency in a dual frequency He-Ne laser varies while the resonant cavity length is tuned. As to the laser with two longitudinal modes, the variation amplitude is commonly less than 500 kHz, proven by experiments and theories. This study reveals an anomalous variation of the beat frequency when a piece of element is put into the cavity and is aligned with the laser axis. Consequently the variation amplitude couM reach 22 MHz, several dozen times larger than that without the intra-cavity element. This cannot be explained only by laser mode pulling and pushing effects. Some influencing factors are investigated experimentally, including the tilted angle of the element and the distance between its surface and cavity mirror. The qualitative analysis is discussed, which agrees with the experimental results.

关键词： of on as it or Anomalous Variation of Beat Frequency in a Dual Frequency He-Ne Laser in is

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Classification of stellar populations in globular clusters

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Research in astronomy and Astrophysics 2017年第5期17卷 107-112页

作者： Yue Wang Gang Zhao Hai-Ning Li Key laboratory of optical astronomy National Astronomical Observatories Chinese Academy of Sciences School of astronomy and Space Science University of Chinese Academy of Sciences

Possessing multiple stellar populations has been accepted as a common feature of globular clusters（GCs）. Different stellar populations manifest themselves with different chemical features,e.g. the well-known O-Na anti-correlation. Generally, the first（primordial） population has O and Na abundances consistent with those of field stars with similar metallicity; while the second（polluted） population is identified by their Na overabundance and O deficiency. The fraction of the populations is an important constraint on the GC formation scenario. Several methods have been proposed for the classification of GC populations. Here we examine a criterion derived based on the distribution of Galactic field stars, which relies on Na abundance as a function of [Fe/H], to distinguish first and second stellar populations in GCs. By comparing the first population fractions of 17 GCs estimated by the field star criterion with those in the literature derived by methods related to individual GCs, we find that the field star criterion tends to overestimate the first population fractions. The population separation methods,which are related to an individual GC sample, are recommended because the diversity of GCs can be taken into consideration. Currently, more caution should be exercised if one wants to regard field stars as a reference for the identification of a GC population. However, further study on the connection between field stars and GCs populations is still needed.

关键词： stellar populations stars criterion distinguish scenario primordial abundance manifest constraint

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