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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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First PPMXL photometric analysis of open cluster Ruprecht 15

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Research in astronomy and Astrophysics 2012年第2期12卷 158-166页

作者： Ashraf Latif Tadross National Research institute of astronomy & geophysics

We present the first in a series studying the astrophysical parameters of open clusters using the PPMXL＊ database whose data are applied to study Ruprecht 15. The astrophysical parameters of Ruprecht 15 have been est... 详细信息

关键词： open clusters and associations (individual: Ruprecht 15) -- astrometry-- stars -- astronomical databases: catalogs

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Spectral Behavior and Flaring Activity ofⅡPeg in the Ultraviolet

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Research in astronomy and Astrophysics 2022年第8期22卷 191-197页

作者： M.R.Sanad astronomy Department National Research Institute of Astronomy and GeophysicsHelwanCairoEgypt

We have studied the spectral behavior of theⅡPeg binary system in the ultraviolet band by using International Ultraviolet Explorer(IUE)observations over the period *** ultraviolet observations reveal indication of flare activity in both chromosphere and transition region with their enhanced emission *** and after the flare activity the ultraviolet emission lines show low,intermediate and high *** spectral behavior is compared with previous *** detect prominent flare activity in 1989,1990 and *** and after this period there is a gradual clear decrease in the level of *** reddening ofⅡPeg was determined from a 2200?absorption feature to be E(B-V)=0.10±*** ascertained the average mass loss rate to be≈1×10^(-8)M_(☉)yr^(-1),and an average ultraviolet luminosity to be≈6×10^(29)erg s^(-1).We attributed the spectral variations to a cyclic behavior of the underlying magnetic dynamo and the prominent activity can be interpreted by the model of a two-ribbon flare.

关键词： line:profiles magnetic fields stars:activity stars:flare ultraviolet:stars

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Inter-Calibration Between Plasma Instruments Onboard DEMETER

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Plasma Science and Technology 2008年第5期10卷 539-545页

作者： Maha S.QUASSIM National Research institute of astronomy and geophysics Helwan 11421CairoEgypt

The in-situ measurements of the ionospheric plasma that we use come from two instruments of the scientific payload of the satellite DEMETER; the plasma analyser IAP （Instrument d＇analyse du plasma） and the Langmuir probe ISL （Instrument Sonde de Langmuir）. DEMETER is a micro-satellite realized by the CNES（Centre National d＇Etudes Spatiales, France） with a principal objective to seek a possible influence of the seismic activity on the electromagnetic waves in the ionosphere and on the ionospheric plasma. The satellite was placed on June 29, 2004, in a circular and quasi helio-synchronous orbit at -710 km altitude. The experiments function primarily at mid-latitudes （from ＋60° to -60°）. The IAP data were analysed to deduce the ion population （densities of the dominant ions, i.e. generally O^＋, H^＋ and He^＋） therefore the total ion density. The use of data IAP thus requires some precaution to make sure that the electric equilibrium conditions of the satellite, such as the satellite potential （Фsat）, are obtained during the treatment of routine, does not induce an error of measurement. When this potential is negative, the minority light ions H^＋ and He^＋ can be measured in a reliable way when their proportion is above 3% to 5% of that of O^＋. The critical limitation is： under certain conditions, the satellite potential becomes positive and reach a value about -0.5 V so that it becomes impossible to measure H^＋ ions. This is likely to involve a significant error on the composition and the density of the plasma. Therefore we carried out a calibration to estimate the missing density. The ISL experiment （Langmuir probe） provided the collected current/polarized tension characteristics of a cylindrical probe from which both electron density Ne and temperature Te were obtained. In some situations it is necessary to examine the accuracy of the electron density using another technique, for instance the high frequency （HF） spectrogram, provided by ICE （instrument champ electrique

关键词： plasma analyser satellite plasma observation ion density measuring

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A New Analysis in the Field of the Open Cluster Collinder 223

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Chinese Journal of astronomy and Astrophysics 2004年第1期4卷 67-74页

作者： A.L.Tadross National Research institute of astronomy and geophysics 11421-Helwan Cairo Egypt

The present study of the open cluster Collinder 223 (Cr 223) depended greatlyon the photoelectric data of Claria and Lapasset. We use the data in conjunction with the AAO/DSS^1image of the cluster in a re-investigation to improve the main parameters of Cr 223, including thestellar density, the position of the cluster's center, the cluster's diameter. Its luminosityfunction, mass function, and total mass are also estimated.

关键词： galaxy: open clusters and associations individual: Cr 223

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Recursive harmonic analysis for computing Hansen coefficients

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Research in astronomy and Astrophysics 2010年第12期10卷 1298-1306页

作者： Mohamed Adel Sharaf Hadia Hassan Selim astronomy Department Faculty of Science King Abdul Aziz University astronomy Department National Research Institute of Astronomy and Geophysics

We report on a simple pure numerical method developed for computing Hansen coefficients by using a recursive harmonic analysis technique. The precision criteria of the computations are very satisfactory and provide materials for computing Hansen＇s and Hansen＇s like expansions, and also to check the accuracy of some existing algorithms.

关键词： celestial mechanics -- methods: numerical

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A Reinvestigation of the Physical Properties of Pismis 3 based on 2MASS Photometry

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Chinese Journal of astronomy and Astrophysics 2008年第3期8卷 362-368页

作者： Tadross A.L. National Research institute of astronomy and geophysics 11421-HelwanCairoEgypt

As a continuation of a series of work, we aim to refine and re-determine the physical parameters of previously rarely or un-studied open star clusters with good quality CMDs using Near-IR JHK photometry. Here we present a morphological analysis of the 2MASS database （the digital ＂Two Micron All Sky Survey＂） for the open cluster Pismis 3. Some of the physical parameters are estimated for the first time, and some others, re-determined.

关键词： techniques photometric -- Galaxy open clusters and associations -- stars luminosity function -- stellar clusters individual Pismis 3

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Stellar Population Analysis of Galaxies based on Genetic Algorithms

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Chinese Journal of astronomy and Astrophysics 2005年第4期5卷 347-355页

作者： Abdel-Fattah Attia H.A.Ismail I.M.Selim A.M.Osman I.A.Isaa M.A.Marie A.A.Shaker National Research institute of astronomy and geophysics(NRIAG) 11421 HelwanCairoEgyptNational Research Institute of Astronomy and Geophysics(NRIAG)11421 HelwanCairoEgypt Cairo University Faculty of ScienceAstronomy DepartmentEgypt

We present a new method for determining the age and relative contribution of different stellar populations in galaxies based on the genetic *** apply this method to the barred spiral galaxy NGC 3384,using CCD images in U,B,V,R and I *** analysis indicates that the galaxy NGC 3384 is mainly inhabited by old stellar population(age〉10^9 yr).Some problems were encountered when numerical simulations are used for determining the contribution of different stellar populations in the integrated color of a *** results show that the proposed genetic algorithm can search efficiently through the very large space of the possible ages.

关键词： methods numerical-galaxies stellar population-galaxies individual(NGC 3384).

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The simplest way to get a cluster's parameters in the Gaia era(Dolidze 41)

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Research in astronomy and Astrophysics 2018年第12期18卷 137-142页

作者： Ashraf Latif Tadross National Research institute of astronomy&geophysics 11421-HelwanCairoEgypt

The astro-photometric parameters of the open star cluster Dolidze 41, which is located in the constellation Cygnus, have been investigated using the Gaia DR2 large survey that is merged with the near infrared Two Micron All Sky Survey(2 MASS) *** radial density distribution(limited,core and tidal radii), color-magnitude diagrams, galactocentric coordinates, distances, color excess and age of Dolidze 41 are *** Gaia DR2 astrometry helped us to define the membership of the cluster stars *** luminosity and mass functions, the entire luminosity and mass, and the relaxation time of the cluster have been estimated as well.

关键词： (Galaxy:) open clusters and associations:individual(Dolidze 41) photometry:Color-Magnitude Diagram astrometry stars:luminosity function mass function astronomical data bases:miscellaneous

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Astrophysical parameters of ten poorly studied open star clusters

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Research in astronomy and Astrophysics 2012年第1期12卷 75-83页

作者： Ashraf Latif Tadross Reda El-Bendary Anas Osman Nader Ismail Abdel Aziz Bakry National Research institute of astronomy & geophysics Faculty of Science Al-Azhar University

We present the fundamental parameters of ten open star clusters, nominated from Kronberger et al. who presented some newly discovered stellar groups on the basis of the Two Micron All Sky Survey photometry and Digitized Sky Survey visual images. Star counts and photometric parameters （radius, membership, distance, color excess, age, luminosity function, mass function, total mass, and dynamical relaxation time） have been determined for these ten clusters for the first time. In order to calibrate our procedures, the main parameters （distance, age, and color excess） have been reestimated for another five clusters, which are also studied by Kronberger et al.

关键词： Galaxy: open clusters and associations: general-- stars: luminosity func-tion mass function -- catalogs surveys -- infrared: stars

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