Early multiwavelength observations offer crucial insights into the nature of the relativistic jets responsible for gamma-ray bursts and their interaction with the surrounding medium.We present data of GRB 240825A from...Early multiwavelength observations offer crucial insights into the nature of the relativistic jets responsible for gamma-ray bursts and their interaction with the surrounding medium.We present data of GRB 240825A from 17 space-and ground-based telescopes/instruments,covering wavelengths from NIR/optical to X-ray and GeV,and spanning from the prompt emission to the afterglow phase triggered by Swift and Fermi.The early afterglow observations were carried out by SVOM/C-GFT,and spectroscopic observations of the afterglow by GTC,VLT,and TNG determined the redshift of the burst(z=0.659)later.A comprehensive analysis of the prompt emission spectrum observed by Swift-BAT and Fermi-GBM/LAT reveals a rare and significant high-energy cutoff at 76 MeV.Assuming this cutoff is due toγγabsorption allows us to place an upper limit on the initial Lorentz factor,Γ_(0)<245.The optical/NIR and GeV afterglow light curves can be described by the standard external shock model,with early-time emission dominated by a reverse shock(RS)and a subsequent transition to forward shock(FS)emission.Our afterglow modeling yields a consistent estimate of the initial Lorentz factor(Γ_(0)∼234).Furthermore,the RS-to-FS magnetic field ratio(R 302B)indicates that the RS region is significantly more magnetized than the FS region.An isotropic-equivalent kinetic energy of E_(k,iso)=5.25×10^(54) erg is derived,and the correspondingγ-ray radiation efficiency is estimated to beη_(γ)=3.1%.On the other hand,the standard afterglow model cannot reproduce the X-ray light curve of GRB 240825A,calling for improved models to characterize all multiwavelength data.展开更多
The discovery of ubiquitous habitable extrasolar planets,combined with revolutionary advances in instrumentation and observational capabilities,has ushered in a renaissance in the search for extraterrestrial intellige...The discovery of ubiquitous habitable extrasolar planets,combined with revolutionary advances in instrumentation and observational capabilities,has ushered in a renaissance in the search for extraterrestrial intelligence(SETI).Large scale SETI activities are now underway at numerous international facilities.The Five-hundred-meter Aperture Spherical radio Telescope(FAST)is the largest single-aperture radio telescope in the world,and is well positioned to conduct sensitive searches for radio emission indicative of exo-intelligence.SETI is one of the five key science goals specified in the original FAST project plan.A collaboration with the Breakthrough Listen Initiative was initiated in 2016 with a joint statement signed both by Dr.Jun Yan,the then director of National Astronomical Observatories,Chinese Academy of Sciences(NAOC),and Dr.Peter Worden,Chairman of the Breakthrough Prize Foundation.In this paper,we highlight some of the unique features of FAST that will allow for novel SETI observations.We identify and describe three different signal types indicative of a technological source,namely,narrow band,wide-band artificially dispersed and modulated signals.Here,we propose observations with FAST to achieve sensitivities never before explored.For nearby exoplanets,such as TESS targets,FAST will be sensitive to an EIRP of 1.9×1011 W,well within the reach of current human technology.For the Andromeda Galaxy,FAST will be able to detect any Kardashev type II or more advanced civilization there.展开更多
Submillimeter interferometry has the potential to image supermassive black holes on event horizon scales,providing tests of the theory of general relativity and increasing our understanding of black hole accretion pro...Submillimeter interferometry has the potential to image supermassive black holes on event horizon scales,providing tests of the theory of general relativity and increasing our understanding of black hole accretion processes.The Event Horizon Telescope(EHT) performs these observations from the ground,and its main imaging targets are Sagittarius A~* in the Galactic Center and the black hole at the center of the M87 galaxy.However,the EHT is fundamentally limited in its performance by atmospheric effects and sparse terrestrial(u,v)-coverage(Fourier sampling of the image).The scientific interest in quantitative studies of the horizon size and shape of these black holes has motivated studies into using space interferometry which is free of these limitations.Angular resolution considerations and interstellar scattering effects push the desired observing frequency to bands above 500 GHz.This paper presents the requirements for meeting these science goals,describes the concept of interferometry from Polar or Equatorial Medium Earth Orbits(PECMEO) which we dub the Event Horizon Imager(EHI),and utilizes suitable space technology heritage.In this concept,two or three satellites orbit at slightly different orbital radii,resulting in a dense and uniform spiral-shaped(u,v)-coverage over time.The local oscillator signals are shared via an inter-satellite link,and the data streams are correlated on-board before final processing on the ground.Inter-satellite metrology and satellite positioning are extensively employed to facilitate the knowledge of the instrument position vector,and its time derivative.The European space heritage usable for both the front ends and the antenna technology of such an instrument is investigated.Current and future sensors for the required inter-satellite metrology are listed.Intended performance estimates and simulation results are given.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
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
基金supported by the National Key R&D Program of China(grant No.2024YFA1611600)the SVOM project(a mission under the Strategic Priority Program on Space Science of the Chinese Academy of Sciences)+23 种基金the Strategic Priority Research Program of the Chinese Academy of Sciences(grant No.XDB0550401)the National Natural Science Foundation of China(NSFC,grant No.12494573)partly supported by Natural Science Foundation of Xinjiang Uygur Autonomous Region(grant No.2024D01D32)Tianshan Talent Training Program(grant No.2023TSYCLJ0053)Tianshan Innovation Team Program(grant No.2024D14015)supported by the Jiangsu Funding Program for Excellent Postdoctoral Talent(grant No.2024ZB110)the Postdoctoral Fellowship Program(grant No.GZC20241916)the General Fund(grant No.2024M763531)of the China Postdoctoral Science Foundationsupported by a Royal Society Dorothy Hodgkin Fellowship(grant Nos.DHF-R1-221175 and DHF-ERE-221005)support by a postdoctoral fellowship from the CNESsupported by the National Key R&D Program of China(grant No.2024YFA1611702)the Strategic Priority Research Program of the Chinese Academy of Sciences(grant No.XDB0550101)the support of the French Agence Nationale de la Recherche(ANR),under grant ANR-23-CE31-0011(project PEGaSUS)financial support from the GRAWITA Large Program Grant(PI P.D’Avanzo)financial support from the Italian Space Agency,contract ASI/INAF No.I/004/11/6support from the INAF project Premiale Supporto Arizona&Italiasupported by the National Natural Science Foundation of China(NSFC,grant No.12133003)supported by the National Natural Science Foundation of China(NSFC,grant No.12373042)the Bagui Scholars Program(No.GXR-6BG2424001)funded by the European Union(ERC,HEAVYMETAL,101071865,Views and opinions expressed are,however,those of the authors only and do not necessarily reflect those of the European Union or the European Research Council Neither the European Union nor the granting authority can be held responsible for them)the Cosmic Dawn Center(DAWN)is funded by the Danish National Research Foundation under grant No.DNRF140supported by the National Natural Science Foundation of China(NSFC,grant Nos.12225305 and 12321003)supported by the National Natural Science Foundation of China(NSFC,grant No.12473049)supported by the General Fund(grant No.2024M763530)of the China Postdoctoral Science Foundation。
文摘Early multiwavelength observations offer crucial insights into the nature of the relativistic jets responsible for gamma-ray bursts and their interaction with the surrounding medium.We present data of GRB 240825A from 17 space-and ground-based telescopes/instruments,covering wavelengths from NIR/optical to X-ray and GeV,and spanning from the prompt emission to the afterglow phase triggered by Swift and Fermi.The early afterglow observations were carried out by SVOM/C-GFT,and spectroscopic observations of the afterglow by GTC,VLT,and TNG determined the redshift of the burst(z=0.659)later.A comprehensive analysis of the prompt emission spectrum observed by Swift-BAT and Fermi-GBM/LAT reveals a rare and significant high-energy cutoff at 76 MeV.Assuming this cutoff is due toγγabsorption allows us to place an upper limit on the initial Lorentz factor,Γ_(0)<245.The optical/NIR and GeV afterglow light curves can be described by the standard external shock model,with early-time emission dominated by a reverse shock(RS)and a subsequent transition to forward shock(FS)emission.Our afterglow modeling yields a consistent estimate of the initial Lorentz factor(Γ_(0)∼234).Furthermore,the RS-to-FS magnetic field ratio(R 302B)indicates that the RS region is significantly more magnetized than the FS region.An isotropic-equivalent kinetic energy of E_(k,iso)=5.25×10^(54) erg is derived,and the correspondingγ-ray radiation efficiency is estimated to beη_(γ)=3.1%.On the other hand,the standard afterglow model cannot reproduce the X-ray light curve of GRB 240825A,calling for improved models to characterize all multiwavelength data.
文摘The discovery of ubiquitous habitable extrasolar planets,combined with revolutionary advances in instrumentation and observational capabilities,has ushered in a renaissance in the search for extraterrestrial intelligence(SETI).Large scale SETI activities are now underway at numerous international facilities.The Five-hundred-meter Aperture Spherical radio Telescope(FAST)is the largest single-aperture radio telescope in the world,and is well positioned to conduct sensitive searches for radio emission indicative of exo-intelligence.SETI is one of the five key science goals specified in the original FAST project plan.A collaboration with the Breakthrough Listen Initiative was initiated in 2016 with a joint statement signed both by Dr.Jun Yan,the then director of National Astronomical Observatories,Chinese Academy of Sciences(NAOC),and Dr.Peter Worden,Chairman of the Breakthrough Prize Foundation.In this paper,we highlight some of the unique features of FAST that will allow for novel SETI observations.We identify and describe three different signal types indicative of a technological source,namely,narrow band,wide-band artificially dispersed and modulated signals.Here,we propose observations with FAST to achieve sensitivities never before explored.For nearby exoplanets,such as TESS targets,FAST will be sensitive to an EIRP of 1.9×1011 W,well within the reach of current human technology.For the Andromeda Galaxy,FAST will be able to detect any Kardashev type II or more advanced civilization there.
基金partly supported by the Project NPI-552 “Space-to-space Interferometer System to Image the Event Horizon of the Super Massive Black Hole in the Center of Our Galaxy” co-funded by the European Space Agency (ESA) and the Radboud University of Nijmegen (ESA contract 4000122812)by the NWO project PIPP “Breakthrough Technologies for Interferometry in Space”。
文摘Submillimeter interferometry has the potential to image supermassive black holes on event horizon scales,providing tests of the theory of general relativity and increasing our understanding of black hole accretion processes.The Event Horizon Telescope(EHT) performs these observations from the ground,and its main imaging targets are Sagittarius A~* in the Galactic Center and the black hole at the center of the M87 galaxy.However,the EHT is fundamentally limited in its performance by atmospheric effects and sparse terrestrial(u,v)-coverage(Fourier sampling of the image).The scientific interest in quantitative studies of the horizon size and shape of these black holes has motivated studies into using space interferometry which is free of these limitations.Angular resolution considerations and interstellar scattering effects push the desired observing frequency to bands above 500 GHz.This paper presents the requirements for meeting these science goals,describes the concept of interferometry from Polar or Equatorial Medium Earth Orbits(PECMEO) which we dub the Event Horizon Imager(EHI),and utilizes suitable space technology heritage.In this concept,two or three satellites orbit at slightly different orbital radii,resulting in a dense and uniform spiral-shaped(u,v)-coverage over time.The local oscillator signals are shared via an inter-satellite link,and the data streams are correlated on-board before final processing on the ground.Inter-satellite metrology and satellite positioning are extensively employed to facilitate the knowledge of the instrument position vector,and its time derivative.The European space heritage usable for both the front ends and the antenna technology of such an instrument is investigated.Current and future sensors for the required inter-satellite metrology are listed.Intended performance estimates and simulation results are given.
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.
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.
