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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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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

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Can FSRQs produce the Ice Cube detected diffuse neutrino emission?

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Science China(Physics,Mechanics & astronomy) 2016年第1期59卷 98-103页

作者： Bin Wang Zhuo Li department of astronomy Peking University kavli institute for astronomy and astrophysics Peking University

IceCube has reported the detection of a diffuse TeV-PeV neutrino emission, for which the flat spectrum radio quasars （FSRQs） have been proposed to be the candidate sources. Here we assume that the neutrino flux from FSRQs is proportional to their gamma-ray ones, and obtain the gamma-ray/neutrino flux ratio by the diffuse gamma-ray flux from Fermi-LAT measurement of FSRQs and the diffuse neutrino flux detected by IceCube. We apply this ratio to individual FSRQs and hence predict their neutrino flux. We find that a large fraction of candidate FSRQs from the northern sky in the IceCube point source search has predicted neutrino flux above the IceCube upper limit; and for the sample of stacking search for neutrinos by IceCube, the predicted stacked flux is even larger than the upper limit of stacked flux by orders of magnitude. Therefore the IceCube limit from stacking searches, combined with the Fermi-LAT observations, already rejects FSRQs as the main sources of IceCube-detected diffuse neutrinos： FSRQs can only account for 〈 10% 〈 4%） of the IceCube-detected diffuse neutrino flux, according to the stacking searches from the whole （northern） sky. The derived small neutrino/gamma-ray flux ratio also implies that the gamma-ray emission from FSRQs cannot be produced by the secondary le^tons and photons from the Non nroduction nrocesses. The caveat in the assumntions is discussed.

关键词： neutrinos gamma rays active and peculiar galaxies and related systems

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Sky location of massive black hole binaries in the foreground of Galactic white dwarf binaries

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Science China(Physics,Mechanics & astronomy) 2025年第1期Mechanics & Astronomy) .卷 97-108页

作者： Pan Guo Hong-Bo Jin Cong-Feng Qiao Yue-Liang Wu The International Centre for Theoretical Physics Asia-Pacific University of Chinese Academy of Sciences The School of Physical Sciences University of Chinese Academy of Sciences institute for Frontiers in astronomy and astrophysics Beijing Normal University National Astronomical Observatories Chinese Academy of Sciences institute of Theoretical Physics Chinese Academy of Sciences

For space-based gravitational wave （GW） detection,the main noise source for massive black hole binaries （MBHBs） is attributed to approximately 10～7double white dwarf binaries in the *** a GW source,the amplitude of the detector response,recorded by a space-based gravitational wave detector,exhibits a modulation effect with a year period when observing the source from various orbital *** the adverse conditions mentioned above,where there is a strong foreground noise and annual modulation in the signals,we employed the wavelet transform and the strong-amplitude relevant orbital position search methods,which allows the weak MBHB sources to achieve higher locating *** detail,for two MBHB sources of lower intensity,the precision of luminosity distance,represented by the ratio ?DL/DLat the 95%confidence level,is enhanced by factors of ～*** angular resolutions,denoted by??s,are enhanced by a factor of ～*** improvements increase the number of detectable GW sources,facilitate multi-messenger follow-up observations and provide constraints on the cosmological constant.

关键词： space-based gravitational wave detection gravitational waves massive black hole binaries

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PeV neutrinos from wind breakouts of type Ⅱ supernovae

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Science China(Physics,Mechanics & astronomy) 2019年第5期62卷 114-120页

作者： Zhuo Li department of astronomy School of Physics Peking University kavli institute for astronomy and astrophysics Peking University

Recently,rapid multiwavelength photometry and flash spectra of supernova(SN)2013fs imply that the progenitor stars of regular type Ⅱ supernovae(SNe Ⅱ)may be commonly surrounded by a confined,dense stellar wind ejected from the progenitor star at a large mass loss rate over few years before the *** on the assumption that the pre-SN progenitor stars of SNe Ⅱ emit wind similar to SN 2013fs,with a mass loss rate■,we investigated neutrino emissions during the wind breakouts of SN *** find that a typical SNe Ⅱ can convert～10^(-3)of their bulk kinetic energy into neutrino emissions,contributing a significant fraction of the IceCube-detected neutrino flux at ■300 ***,■200 TeV IceCube neutrinos can be accounted for by the cosmic rays produced by shocks of all SN remnants,losing energy in their host galaxies,i.e.,the starburst *** future follow-up observations of high energy neutrinos and gamma-rays from nearby individual SNe Ⅱ,days to weeks after the explosions,will test this model.

关键词： neutrinos gamma rays supernovae

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Search for strong gravitational lensing effect in the current GRB data of BATSE

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Science China(Physics,Mechanics & astronomy) 2014年第8期57卷 1592-1599页

作者： LI ChunYu LI LiXin department of astronomy Peking University kavli institute for astronomy and astrophysics Peking University

Because gamma-ray bursts （GRBs） trace the high-z universe, there is an appreciable probability for a GRB to be gravitational lensed by galaxies in the universe. Herein we consider the gravitational lensing effect of GRBs contributed by the dark matter halos in galaxies. Assuming that all halos have the singular isothermal sphere （SIS） mass profile in the mass range 101~h 1Mo 〈 M 〈 2×10^13h^-1M and all GRB samples follow the intrinsic redshift distribution and luminosity function derived from the Swift LGRBs sample, we calculated the gravitational lensing probability in BATSE, Swift/BAT and Fermi/GBM GRBs, re- spectively. With an derived probability result in BATSE GRBs, we searched for lensed GRB pairs in the BATSE5B GRB Spectral catalog. The search did not find any convincing gravitationally lensed events. We discuss our result and future obser- vations for GRB lensing observation.

关键词： star formation galactic halos gravitational lenses and luminous arcs γ-ray sources γ-ray bursts cosmology

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Constraining fast radio burst progenitors with gravitational lensing

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Science China(Physics,Mechanics & astronomy) 2014年第7期57卷 1390-1394页

作者： LI ChunYu LI LiXin department of astronomy Peking University kavli institute for astronomy and astrophysics Peking University

Fast Radio Bursts(FRBs)are new transient radio sources discovered *** of the angular resolution restriction in radio surveys,no optical counter part has been identified yet so it is hard to determine the progenitor of *** this paper we propose to use radio lensing survey to constrain FRB *** show that,different types of progenitors lead to different probabilities for a FRB to be gravitationally lensed by dark matter halos in foreground galaxies,since different type progenitors result in different redshift distributions of *** example,the redshift distribution of FRBs arising from double stars shifts toward lower redshift than of the FRBs arising from single stars,because double stars and single stars have different evolution *** detailed calculations,we predict that the FRB sample size for producing one lensing event varies significantly for different FRB progenitor *** argue that this fact can be used to distinguish different FRB models and also discuss the practical possibility of using lensing observation in radio surveys to constrain FRB progenitors.

关键词： star formation radio sources gravitational lenses and luminous arcs cosmology

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Extremely metal-poor star candidates in the SDSS

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Research in astronomy and astrophysics 2013年第3期13卷 313-322页

作者： Si-Yao Xu Hua-Wei Zhang Xiao-Wei Liu department of astronomy School of Physics Peking University kavli institute of astronomy and astrophysics Peking University

For a sample of metal-poor stars （-3.3 ≤ [Fe/H] ≤-2.2） that have highresolution spectroscopic abundance determinations, we have measured equivalent widths of the Ca II K, Mg I b and near-infrared Ca II triplet lines using low-resolution spectra from the Sloan Digital Sky Survey （SDSS）, calculated effective temperatures from （g - z）o color, deduced stellar surface gravities by fitting stellar isochrones, and determined metallicities based on the aforementioned quantities. Metallicities thus derived from the Ca II K line are in much better agreement with the results deter- mined from high-resolution spectra than the values given in the SDSS Data Release 7. The metallicities derived from the Mg I b lines have a large dispersion owing to the large measurement errors, whereas those deduced from the Ca II triplet lines are too high due to both non-local thermodynamical equilibrium （NLTE） effects and mea- surement errors. Abundances after correction for the NLTE effect for the Mg I b lines and Ca II triplet lines are also presented. Following this method, we have identified six candidates of ultra-metal-poor stars with [Fe/H] - -4.0 from a sample of 166 metal-poor star candidates. One of them, SDSS J102915＋172927, was recently con- firmed to be an ultra-metal-poor （[Fe/H] 〈 -4.0） star with the lowest metallicity ever measured. Follow-up high-resolution spectroscopy for the other five ultra-metal-poor stars in our sample will therefore be of great interest.

关键词： stars: abundances -- stars: Population -- techniques: spectroscopic

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Recent Developments on the H_(I)Gas of Low-Redshift Galaxies Seen by the 21 cm Emission Lines

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Chinese Physics Letters 2024年第10期41卷 152-165页

作者： Jing Wang Xuchen Lin kavli institute for astronomy and astrophysics Peking UniversityBeijing 100871China department of astronomy School of PhysicsPeking UniversityBeijing 100871China

As a major interstellar medium,the atomic neutral hydrogen(H_(I))plays an important role in the galaxy *** provides the ingredient for star formation,and sensitively traces the internal processes and external perturbations influencing the *** the beginning of many new radio telescopes and surveys,H_(I)may make a more significant contribution to the understanding of galaxies in the near *** review discusses the major development of the 21 cm emission-line H_(I)observations and studies in the past few years,including its scaling relations with other galaxy properties,its kinematics and structures,its role in environmental studies,and its constraints on hydrodynamical *** local-Universe H_(I)scaling relations of stellar-massselected samples extend smoothly to 10^(9)M⊙stellar mass,with a tentative evolution to the redshift of∼*** development of measurement techniques enables better estimations of H_(I)non-circular motion,dispersion,and thickness,and new observations revealed extended or extra-planar H_(I)structures,both helpfully constraining the gas accretion,stellar feedback,and star formation processes of galaxy evolution models.H_(I)is very useful for tracing the satellite evolution in dense environments,the studies of which would benefit from ongoing blind H_(I)*** simulations still cannot fully reproduce H_(I)gas properties,they help to understand the role of possible factors in regulating H_(I)properties.

关键词： evolution. galaxy stellar

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Photon diffusion in a relativistically expanding sphere

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Frontiers of physics 2013年第5期8卷 555-563页

作者： Li-Xin Li kavli institute for astronomy and astrophysics Peking University Beijing 100871 China

A relativistically expanding sphere exists ill many explosive astrophysical systelns, including gamma ray bursts, neutron star mergers, and some supernovae. In this paper we investigate the photon diffusion process in a relativistically expanding sphere, which is important for understanding the energetic and radiative characters of the above inentioned explosive systenls. The following contents are discussed in the frame work of special relativity： random walks of photons by scattering witti electrons, photospheres, photon diffusion, and the energy flux density emerging from the surface of the expanding sphere. Some of the results are also applicable to the Universe since the Universe is also a spherical expanding system.

关键词： special relativity explosive processes gamma-ray bursts supernovae neutron starmergers radiative transfer scattering cosmology

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