Distribution of Gamma-ray Burst Ejecta Energy with Lorentz Factor

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The early X-ray afterglow for a significant number of gamma-ray bursts detected by the Swift satellite is observed to have a phase of very slow flux decline with time (F{sub {nu}} {proportional_to} t{sup -{alpha}} with 0.2 {approx}< {alpha} {approx}< 0.8) for 10{sup 2.5} s{approx}< t {approx}< 10{sup 4} s, while the subsequent decline is the usual 1 {approx}< {alpha}{sub 3} {approx}< 1.5 behavior, that was seen in the pre-Swift era. We show that this behavior is a natural consequence of a small spread in the Lorentz factor of the ejecta, by a factor of {approx} 2-4, where the slower ejecta ... continued below

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9 pages

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Granot, Jonathan & Kumar, Pawan October 7, 2005.

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The early X-ray afterglow for a significant number of gamma-ray bursts detected by the Swift satellite is observed to have a phase of very slow flux decline with time (F{sub {nu}} {proportional_to} t{sup -{alpha}} with 0.2 {approx}< {alpha} {approx}< 0.8) for 10{sup 2.5} s{approx}< t {approx}< 10{sup 4} s, while the subsequent decline is the usual 1 {approx}< {alpha}{sub 3} {approx}< 1.5 behavior, that was seen in the pre-Swift era. We show that this behavior is a natural consequence of a small spread in the Lorentz factor of the ejecta, by a factor of {approx} 2-4, where the slower ejecta gradually catch-up with the shocked external medium, thus increasing the energy of forward shock and delaying its deceleration. The end of the ''shallow'' flux decay stage marks the beginning of the Blandford-McKee self similar external shock evolution. This suggests that most of the energy in the relativistic outflow is in material with a Lorentz factor of {approx} 30-50.

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9 pages

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  • Journal Name: Monthly Notices of the Royal Astronomical Society; Journal Volume: 366; Journal Issue: 9

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  • Report No.: SLAC-PUB-11515
  • Grant Number: AC02-76SF00515
  • Office of Scientific & Technical Information Report Number: 878085
  • Archival Resource Key: ark:/67531/metadc876998

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  • October 7, 2005

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  • Sept. 21, 2016, 2:29 a.m.

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  • Dec. 5, 2016, 2:25 p.m.

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Granot, Jonathan & Kumar, Pawan. Distribution of Gamma-ray Burst Ejecta Energy with Lorentz Factor, article, October 7, 2005; [Menlo Park, California]. (digital.library.unt.edu/ark:/67531/metadc876998/: accessed August 20, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.