GRB radiative efficiencies derived from the swift data: GRBs versus XRFs, long versus short

Bing Zhang, Enwei Liang, Kim L. Page, Dirk Grupe, Bin Bin Zhang, Scott D. Barthelmy, David Nelson Burrows, Sergio Campana, Guido Chincarini, Neil Gehrels, Shiho Kobayashi, Peter Istvan Meszaros, Alberto Moretti, John Andrew Nousek, Paul T. O'Brien, Julian P. Osborne, Peter W.A. Roming, Takanori Sakamoto, Patricia Schady, Richard Willingale

Research output: Contribution to journalArticle

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Abstract

We systematically analyze the prompt emission and the early afterglow data of a sample of 31 GRBs detected by Swift before 2005 September and estimate the GRB radiative efficiency. B AT'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 efficiencies previously derived from the late-time X-ray data were not reliable. We calculate two radiative efficiencies using the afterglow kinetic energy EK derived at the putative deceleration time (tdec) and at the break time (tb), 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 tdec, 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 εe = 0.1, we find ηγ(tb) usually <10% and ηγ(tdec) varying from a few percent 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 εB and/or a very low ambient density n.

Original languageEnglish (US)
Pages (from-to)989-1001
Number of pages13
JournalAstrophysical Journal
Volume655
Issue number2 I
DOIs
StatePublished - Feb 1 2007

Fingerprint

afterglows
X-ray fluorescence
cooling
x rays
injection
kinetic energy
hardness
energy
deceleration
estimates
narrowband
bursts
shock
decay
parameter

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Zhang, B., Liang, E., Page, K. L., Grupe, D., Zhang, B. B., Barthelmy, S. D., ... Willingale, R. (2007). GRB radiative efficiencies derived from the swift data: GRBs versus XRFs, long versus short. Astrophysical Journal, 655(2 I), 989-1001. https://doi.org/10.1086/510110
Zhang, Bing ; Liang, Enwei ; Page, Kim L. ; Grupe, Dirk ; Zhang, Bin Bin ; Barthelmy, Scott D. ; Burrows, David Nelson ; Campana, Sergio ; Chincarini, Guido ; Gehrels, Neil ; Kobayashi, Shiho ; Meszaros, Peter Istvan ; Moretti, Alberto ; Nousek, John Andrew ; O'Brien, Paul T. ; Osborne, Julian P. ; Roming, Peter W.A. ; Sakamoto, Takanori ; Schady, Patricia ; Willingale, Richard. / GRB radiative efficiencies derived from the swift data : GRBs versus XRFs, long versus short. In: Astrophysical Journal. 2007 ; Vol. 655, No. 2 I. pp. 989-1001.
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Zhang, B, Liang, E, Page, KL, Grupe, D, Zhang, BB, Barthelmy, SD, Burrows, DN, Campana, S, Chincarini, G, Gehrels, N, Kobayashi, S, Meszaros, PI, Moretti, A, Nousek, JA, O'Brien, PT, Osborne, JP, Roming, PWA, Sakamoto, T, Schady, P & Willingale, R 2007, 'GRB radiative efficiencies derived from the swift data: GRBs versus XRFs, long versus short', Astrophysical Journal, vol. 655, no. 2 I, pp. 989-1001. https://doi.org/10.1086/510110

GRB radiative efficiencies derived from the swift data : GRBs versus XRFs, long versus short. / Zhang, Bing; Liang, Enwei; Page, Kim L.; Grupe, Dirk; Zhang, Bin Bin; Barthelmy, Scott D.; Burrows, David Nelson; Campana, Sergio; Chincarini, Guido; Gehrels, Neil; Kobayashi, Shiho; Meszaros, Peter Istvan; Moretti, Alberto; Nousek, John Andrew; O'Brien, Paul T.; Osborne, Julian P.; Roming, Peter W.A.; Sakamoto, Takanori; Schady, Patricia; Willingale, Richard.

In: Astrophysical Journal, Vol. 655, No. 2 I, 01.02.2007, p. 989-1001.

Research output: Contribution to journalArticle

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AU - Zhang, Bing

AU - Liang, Enwei

AU - Page, Kim L.

AU - Grupe, Dirk

AU - Zhang, Bin Bin

AU - Barthelmy, Scott D.

AU - Burrows, David Nelson

AU - Campana, Sergio

AU - Chincarini, Guido

AU - Gehrels, Neil

AU - Kobayashi, Shiho

AU - Meszaros, Peter Istvan

AU - Moretti, Alberto

AU - Nousek, John Andrew

AU - O'Brien, Paul T.

AU - Osborne, Julian P.

AU - Roming, Peter W.A.

AU - Sakamoto, Takanori

AU - Schady, Patricia

AU - Willingale, Richard

PY - 2007/2/1

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N2 - We systematically analyze the prompt emission and the early afterglow data of a sample of 31 GRBs detected by Swift before 2005 September and estimate the GRB radiative efficiency. B AT'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 efficiencies previously derived from the late-time X-ray data were not reliable. We calculate two radiative efficiencies using the afterglow kinetic energy EK derived at the putative deceleration time (tdec) and at the break time (tb), 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 tdec, 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 εe = 0.1, we find ηγ(tb) usually <10% and ηγ(tdec) varying from a few percent 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 εB and/or a very low ambient density n.

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Zhang B, Liang E, Page KL, Grupe D, Zhang BB, Barthelmy SD et al. GRB radiative efficiencies derived from the swift data: GRBs versus XRFs, long versus short. Astrophysical Journal. 2007 Feb 1;655(2 I):989-1001. https://doi.org/10.1086/510110