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
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.
