GRB Radiative Efficiencies Derived from the Swift Data: GRBs vs. XRFs, Long vs. Short

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dc.creatorZhang, Bing
dc.creatorLiang, Enwei
dc.creatorPage, Kim L.
dc.creatorGrupe, Dirk
dc.creatorZhang, Bin-Bin
dc.creatorBarthelmy, Scott D.
dc.creatorBurrows, David N.
dc.creatorCampana, Sergio
dc.creatorChincarini, Guido
dc.creatorGehrels, Neil
dc.creatorKobayashi, Shiho
dc.creatorMeszaros, Peter
dc.creatorMoretti, Alberto
dc.creatorNousek, John A.
dc.creatorO'Brien, Paul T.
dc.creatorOsborne, Julian P.
dc.creatorRoming, Peter W. A.
dc.creatorSakamoto, Takanori
dc.creatorSchady, Patricia
dc.creatorWillingale, Richard
dc.date2006-10-05
dc.date.accessioned2026-07-07T10:40:23Z
dc.date.available2026-07-07T10:40:23Z
dc.descriptionWe systematically analyze the prompt emission and the early afterglow data of a sample of 31 GRBs detected by {\em Swift} before September 2005, 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 hardness 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 efficiency previously derived from the late-time X-ray data were not reliable. We calculate two radiative efficiencies using the afterglow kinetic energy E_K derived at the putative deceleration time t_{dec}) and at the break time (t_b) when the energy injection phase ends, respectively. At t_b XRFs appear to be less efficient than normal GRBs. However, when we analyze the data at t_{dec} XRFs are found to be as efficient as GRBs. Short GRBs have similar radiative efficiencies to long GRBs despite of their different progenitors. Twenty-two bursts in the sample are identified to have the afterglow cooling frequency below the X-ray band. Assuming ε_e = 0.1, we find η_γ(t_b) usually <10% and η_γ(t_{dec}) varying from a few percents to > 90%. Nine GRBs in the sample have the afterglow cooling frequency above the X-ray band for a very long time. This suggests a very small ε_B and/or a very low ambient density n.
dc.description43 pages, 10 figures, ApJ, in press
dc.identifierhttps://arxiv.org/abs/astro-ph/0610177
dc.identifierhttp://arxiv.org/abs/astro-ph/0610177
dc.identifierAstrophys.J.655:989-1001,2007
dc.identifierdoi:10.1086/510110
dc.identifier.urihttp://salesiana.dossiersoluciones.com/handle/123456789/181322
dc.subjectAstrophysics
dc.titleGRB Radiative Efficiencies Derived from the Swift Data: GRBs vs. XRFs, Long vs. Short
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