Статья

GRB Radiative Efficiencies Derived from the<i>Swift</i>Data: GRBs versus XRFs, Long versus Short

Bing ZhangDepartment of Physics, University of Nevada, Las Vegas, NVEn‐Wei LiangDepartment of Physics, Guangxi University, Nanning, ChinaK. L. PageDepartment of Physics and Astronomy, University of Leicester, Leicester, UKD. GrupeDepartment of Astronomy and Astrophysics, Pennsylvania State University, University Park, PABin‐Bin ZhangDepartment of Physics, University of Nevada, Las Vegas, NVA. P. BeardmoreNASA/Goddard Space Flight Center, Greenbelt, MDD. N. BurrowsDepartment of Astronomy and Astrophysics, Pennsylvania State University, University Park, PAS. CampanaNASA/Goddard Space Flight Center, Greenbelt, MDG. ChincariniDipartmento di Fisica, Univeritá degli studi Milano-Bicocca, Milan, ItalyN. GehrelsNASA/Goddard Space Flight Center, Greenbelt, MDS. KobayashiAstrophysics Research Institute, Liverpool John Moores University, Birkenhead, UKP. MészárosDepartment of Astronomy and Astrophysics, Pennsylvania State University, University Park, PAA. MorettiINAF-Osservatorio Astronomico di Brera, Merate, ItalyJ. A. NousekDepartment of Astronomy and Astrophysics, Pennsylvania State University, University Park, PAP. T. O’BrienDepartment of Physics and Astronomy, University of Leicester, Leicester, UKJ. P. OsborneDepartment of Physics and Astronomy, University of Leicester, Leicester, UKPeter W. A. RomingDepartment of Astronomy and Astrophysics, Pennsylvania State University, University Park, PAT. SakamotoNASA/Goddard Space Flight Center, Greenbelt, MDP. SchadyDepartment of Astronomy and Astrophysics, Pennsylvania State University, University Park, PAR. WillingaleDepartment of Physics and Astronomy, University of Leicester, Leicester, UK

2007en

ABI

Аннотация

We systematically analyze the prompt emission and the early afterglow data of a sample of 31 GRBs detected by\nSwift before 2005 September and estimate the GRB radiative efficiency. BAT’s narrow band inhibits a precise determination of the GRB spectral parameters, and we have developed a method to estimate these parameters with the\nhardness ratio information. The shallow decay component commonly existing in early X-ray afterglows, if interpreted as continuous energy injection in the external shock, suggests that the GRB efficiencies previously derived\nfrom the late-time X-ray data were not reliable. We calculate two radiative efficiencies using the afterglow kinetic\nenergy EK derived at the putative deceleration time (tdec) and at the break time (tb), when the energy injection phase\nends, respectively. At tb XRFs appear to be less efficient than normal GRBs. However, when we analyze the data at\ntdec, XRFs are found to be as efficient as GRBs. Short GRBs have similar radiative efficiencies to long GRBs despite\nof their different progenitors. Twenty-two bursts in the sample are identified to have the afterglow cooling frequency\nbelow the X-ray band. εe = 0.1, we find ηγ(tb) usually <10% and ηγ(tdec) varying from a few percent to\n>90%. Nine GRBs in the sample have the afterglow cooling frequency above the X-ray band for a very long time.\nThis suggests a very small εB and/or a very low ambient density n.

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Идентификаторы

DOI: 10.1086/510110

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Цитирований: 4Использованных источников: 0

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