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 telescopes.The new transient was fi...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 telescopes.The 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 12 s.The flare reached a peak flux of 3:9×10^(−9) erg cm^(−2) s^(−1) in 0.5-4 keV,∼300 times brighter than the underlying X-ray emission detected throughout the observation.Rapid and more precise follow-up observations by EP/FXT,Swift and NICER confirmed the finding of this new transient.Its X-ray spectrum is non-thermal in 0.5-10 keV,with a power-law photon index varying within 1.8-2.5.The X-ray light curve shows a plateau lasting for∼4 d,followed by a steep decay till becoming undetectable∼10 d after the initial detection.Based 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 transients.No 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 bands.We 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 transients.The nature of EP240408a thus remains an enigma.We suggest that EP240408a may represent a new type of transients with intermediate timescales of the order of∼10 d.The detection and follow-ups of more of such objects are essential for revealing their origin.展开更多
In this White Paper we present the potential of the enhanced X-ray Timing and Polarimetry(eXTP) mission for studies related to Observatory Science targets. These include flaring stars, supernova remnants, accreting wh...In this White Paper we present the potential of the enhanced X-ray Timing and Polarimetry(eXTP) mission for studies related to Observatory Science targets. These include flaring stars, supernova remnants, accreting white dwarfs, low and high mass X-ray binaries, radio quiet and radio loud active galactic nuclei, tidal disruption events, and gamma-ray bursts. eXTP will be excellently suited to study one common aspect of these objects: their often transient nature. Developed by an international Consortium led by the Institute of High Energy Physics of the Chinese Academy of Science, the eXTP mission is expected to be launched in the mid 2020s.展开更多
In this paper we describe the potential of the enhanced X-ray Timing and Polarimetry(eXTP) mission for studies related to accretion flows in the strong field gravity regime around both stellar-mass and supermassive bl...In this paper we describe the potential of the enhanced X-ray Timing and Polarimetry(eXTP) mission for studies related to accretion flows in the strong field gravity regime around both stellar-mass and supermassive black-holes. eXTP has the unique capability of using advanced "spectral-timing-polarimetry" techniques to analyze the rapid variations with three orthogonal diagnostics of the flow and its geometry, yielding unprecedented insight into the inner accreting regions, the effects of strong field gravity on the material within them and the powerful outflows which are driven by the accretion process.展开更多
The Einstein Probe(EP)is an interdisciplinary mission of time-domain and X-ray astronomy.Equipped with a wide-field lobstereye X-ray focusing imager,EP will discover cosmic X-ray transients and monitor the X-ray varia...The Einstein Probe(EP)is an interdisciplinary mission of time-domain and X-ray astronomy.Equipped with a wide-field lobstereye X-ray focusing imager,EP will discover cosmic X-ray transients and monitor the X-ray variability of known sources in 0.5-4 keV,at a combination of detecting sensitivity and cadence that is not accessible to the previous and current wide-field monitoring missions.EP can perform quick characterisation of transients or outbursts with a Wolter-I X-ray telescope onboard.In this paper,the science objectives of the EP mission are presented.EP is expected to enlarge the sample of previously known or predicted but rare types of transients with a wide range of timescales.Among them,fast extragalactic transients will be surveyed systematically in soft X-rays,which includeγ-ray bursts and their variants,supernova shock breakouts,and the predicted X-ray transients associated with binary neutron star mergers.EP will detect X-ray tidal disruption events and outbursts from active galactic nuclei,possibly at an early phase of the flares for some.EP will monitor the variability and outbursts of X-rays from white dwarfs,neutron stars and black holes in our and neighbouring galaxies at flux levels fainter than those detectable by the current instruments,and is expected to discover new objects.A large sample of stellar X-ray flares will also be detected and characterised.In the era of multi-messenger astronomy,EP has the potential of detecting the possible X-ray counterparts of gravitational wave events,neutrino sources,and ultra-high energyγ-ray and cosmic ray sources.EP is expected to help advance the studies of extreme objects and phenomena revealed in the dynamic X-ray universe,and their underlying physical processes.Besides EP's strength in time-domain science,its follow-up telescope,with excellent performance,will also enable advances in many areas of X-ray astronomy.展开更多
基金based on data obtained with Einstein Probe,a space mission supported by Strategic Priority Program on Space Science of Chinese Academy of Sciences,in collaboration with ESA,MPE and CNES(Grant No.XDA15310000)the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDB0550200)+5 种基金the National Key R&D Program of China(Grant No.2022YFF0711500)the support by the National Natural Science Foundation of China(Grant Nos.12333004,12321003,12103065,12373040,12021003,12025303,12393814,and 12203071)the China Manned Space Project(Grant Nos.CMS-CSST-2021-A13,and CMS-CSST-2021-B11)the Youth Innovation Promotion Association of the Chinese Academy of Sciencessupported by a Ramón y Cajal fellowship(Grant No.RYC2021-030888-I)financial support from AGAUR,CSIC,MCIN and AEI 10.13039/501100011033(Grant Nos.PID2023-151307NB-I00,PIE 20215AT016,CEX2020-001058-M,and 2021-SGR-01270)。
文摘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 telescopes.The 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 12 s.The flare reached a peak flux of 3:9×10^(−9) erg cm^(−2) s^(−1) in 0.5-4 keV,∼300 times brighter than the underlying X-ray emission detected throughout the observation.Rapid and more precise follow-up observations by EP/FXT,Swift and NICER confirmed the finding of this new transient.Its X-ray spectrum is non-thermal in 0.5-10 keV,with a power-law photon index varying within 1.8-2.5.The X-ray light curve shows a plateau lasting for∼4 d,followed by a steep decay till becoming undetectable∼10 d after the initial detection.Based 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 transients.No 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 bands.We 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 transients.The nature of EP240408a thus remains an enigma.We suggest that EP240408a may represent a new type of transients with intermediate timescales of the order of∼10 d.The detection and follow-ups of more of such objects are essential for revealing their origin.
基金supported by the Royal Society,ERC Starting(Grant No.639217)he European Union Horizon 2020 Research and Innovation Programme under the Marie Sklodowska-Curie Global Fellowship(Grant No.703916)+10 种基金the National Natural Science Foundation of China(Grant Nos.11233001,11773014,11633007,11403074,11333005,11503008,and 11590781)the National Basic Research Program of China(Grant No.2015CB857100)NASA(Grant No.NNX13AD28A)an ARC Future Fellowship(Grant No.FT120100363)the National Science Foundation(Grant No.PHY-1430152)the Spanish MINECO(Grant No.AYA2016-76012-C3-1-P)the ICCUB(Unidad de Excelencia’Maria de Maeztu’)(Grant No.MDM-2014-0369)EU’s Horizon Programme through a Marie Sklodowska-Curie Fellowship(Grant No.702638)the Polish National Science Center(Grant Nos.2015/17/B/ST9/03422,2015/18/M/ST9/00541,2013/10/M/ST9/00729,and 2015/18/A/ST9/00746)the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDA15020100)the NWO Veni Fellowship(Grant No.639.041.647)
文摘In this White Paper we present the potential of the enhanced X-ray Timing and Polarimetry(eXTP) mission for studies related to Observatory Science targets. These include flaring stars, supernova remnants, accreting white dwarfs, low and high mass X-ray binaries, radio quiet and radio loud active galactic nuclei, tidal disruption events, and gamma-ray bursts. eXTP will be excellently suited to study one common aspect of these objects: their often transient nature. Developed by an international Consortium led by the Institute of High Energy Physics of the Chinese Academy of Science, the eXTP mission is expected to be launched in the mid 2020s.
基金financial contribution from the agreement ASI-INAF n.2017-14-H.Osupport of the Chinese Academy of Sciences through the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDA15020100)the Polish National Science Centre(Grant No.2013/10/M/ST9/00729)
文摘In this paper we describe the potential of the enhanced X-ray Timing and Polarimetry(eXTP) mission for studies related to accretion flows in the strong field gravity regime around both stellar-mass and supermassive black-holes. eXTP has the unique capability of using advanced "spectral-timing-polarimetry" techniques to analyze the rapid variations with three orthogonal diagnostics of the flow and its geometry, yielding unprecedented insight into the inner accreting regions, the effects of strong field gravity on the material within them and the powerful outflows which are driven by the accretion process.
基金supported by Strategic Priority Program on Space Science of Chinese Academy of Sciences,in collaboration with ESA,MPE and CNES(Grant Nos.XDA15310000,and XDA15052100)supported by the National Natural Science Foundation of China(Grant Nos.61234003,61434004,and 61504141)CAS Interdisciplinary Project(Grant No.KJZD-EW-L11-04)。
文摘The Einstein Probe(EP)is an interdisciplinary mission of time-domain and X-ray astronomy.Equipped with a wide-field lobstereye X-ray focusing imager,EP will discover cosmic X-ray transients and monitor the X-ray variability of known sources in 0.5-4 keV,at a combination of detecting sensitivity and cadence that is not accessible to the previous and current wide-field monitoring missions.EP can perform quick characterisation of transients or outbursts with a Wolter-I X-ray telescope onboard.In this paper,the science objectives of the EP mission are presented.EP is expected to enlarge the sample of previously known or predicted but rare types of transients with a wide range of timescales.Among them,fast extragalactic transients will be surveyed systematically in soft X-rays,which includeγ-ray bursts and their variants,supernova shock breakouts,and the predicted X-ray transients associated with binary neutron star mergers.EP will detect X-ray tidal disruption events and outbursts from active galactic nuclei,possibly at an early phase of the flares for some.EP will monitor the variability and outbursts of X-rays from white dwarfs,neutron stars and black holes in our and neighbouring galaxies at flux levels fainter than those detectable by the current instruments,and is expected to discover new objects.A large sample of stellar X-ray flares will also be detected and characterised.In the era of multi-messenger astronomy,EP has the potential of detecting the possible X-ray counterparts of gravitational wave events,neutrino sources,and ultra-high energyγ-ray and cosmic ray sources.EP is expected to help advance the studies of extreme objects and phenomena revealed in the dynamic X-ray universe,and their underlying physical processes.Besides EP's strength in time-domain science,its follow-up telescope,with excellent performance,will also enable advances in many areas of X-ray astronomy.
