The nature of the outflow in gamma-ray bursts

P. Kumar, E. McMahon, A. Panaitescu, R. Willingale, P. O'Brien, David Nelson Burrows, J. Cummings, N. Gehrels, S. Holland, S. B. Pandey, D. Vanden Berk, S. Zane

Research output: Contribution to journalLetter

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Abstract

The Swift satellite has enabled us to follow the evolution of gamma-ray burst (GRB) fireballs from the prompt γ-ray emission to the afterglow phase. The early-time X-ray and optical data for GRBs obtained by telescopes aboard the Swift satellite show that the source for prompt γ-ray emission, the emission that heralds these bursts, is short lived, and is distinct from the source for the long-lived afterglow emission that follows the initial burst. Using these data we determine the distance of the γ-ray source from the centre of the explosion. We find this distance to be 1015-1016 cm for most bursts, and show that this is within a factor of about 10 of the radius of the shock heated circumstellar medium (CSM) producing the X-ray photons. Furthermore, using the early γ-ray, X-ray and optical data we show that the prompt gamma-ray emission cannot be produced in internal shocks nor can it be produced in the external shock; in a more general sense γ-ray generation mechanisms based on shock physics have problems explaining the GRB data for ten Swift bursts analyzed in this work. A magnetic field dominated outflow model for GRBs has a number of attractive features, although evidence in its favour is inconclusive. Finally, the X-ray and optical data allow us to provide an upper limit on the density of the CSM of about 10 protons cmr3 at a distance of ~5 × 1016 cm from the centre of explosion.

Original languageEnglish (US)
JournalMonthly Notices of the Royal Astronomical Society: Letters
Volume376
Issue number1
DOIs
StatePublished - Mar 1 2007

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gamma ray bursts
rays
outflow
bursts
shock
afterglows
explosions
explosion
x rays
fireballs
physics
gamma rays
telescopes
magnetic field
radii
protons
photons
magnetic fields

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Kumar, P. ; McMahon, E. ; Panaitescu, A. ; Willingale, R. ; O'Brien, P. ; Burrows, David Nelson ; Cummings, J. ; Gehrels, N. ; Holland, S. ; Pandey, S. B. ; Vanden Berk, D. ; Zane, S. / The nature of the outflow in gamma-ray bursts. In: Monthly Notices of the Royal Astronomical Society: Letters. 2007 ; Vol. 376, No. 1.
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abstract = "The Swift satellite has enabled us to follow the evolution of gamma-ray burst (GRB) fireballs from the prompt γ-ray emission to the afterglow phase. The early-time X-ray and optical data for GRBs obtained by telescopes aboard the Swift satellite show that the source for prompt γ-ray emission, the emission that heralds these bursts, is short lived, and is distinct from the source for the long-lived afterglow emission that follows the initial burst. Using these data we determine the distance of the γ-ray source from the centre of the explosion. We find this distance to be 1015-1016 cm for most bursts, and show that this is within a factor of about 10 of the radius of the shock heated circumstellar medium (CSM) producing the X-ray photons. Furthermore, using the early γ-ray, X-ray and optical data we show that the prompt gamma-ray emission cannot be produced in internal shocks nor can it be produced in the external shock; in a more general sense γ-ray generation mechanisms based on shock physics have problems explaining the GRB data for ten Swift bursts analyzed in this work. A magnetic field dominated outflow model for GRBs has a number of attractive features, although evidence in its favour is inconclusive. Finally, the X-ray and optical data allow us to provide an upper limit on the density of the CSM of about 10 protons cmr3 at a distance of ~5 × 1016 cm from the centre of explosion.",
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Kumar, P, McMahon, E, Panaitescu, A, Willingale, R, O'Brien, P, Burrows, DN, Cummings, J, Gehrels, N, Holland, S, Pandey, SB, Vanden Berk, D & Zane, S 2007, 'The nature of the outflow in gamma-ray bursts', Monthly Notices of the Royal Astronomical Society: Letters, vol. 376, no. 1. https://doi.org/10.1111/j.1365-2966.2007.00286.x

The nature of the outflow in gamma-ray bursts. / Kumar, P.; McMahon, E.; Panaitescu, A.; Willingale, R.; O'Brien, P.; Burrows, David Nelson; Cummings, J.; Gehrels, N.; Holland, S.; Pandey, S. B.; Vanden Berk, D.; Zane, S.

In: Monthly Notices of the Royal Astronomical Society: Letters, Vol. 376, No. 1, 01.03.2007.

Research output: Contribution to journalLetter

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T1 - The nature of the outflow in gamma-ray bursts

AU - Kumar, P.

AU - McMahon, E.

AU - Panaitescu, A.

AU - Willingale, R.

AU - O'Brien, P.

AU - Burrows, David Nelson

AU - Cummings, J.

AU - Gehrels, N.

AU - Holland, S.

AU - Pandey, S. B.

AU - Vanden Berk, D.

AU - Zane, S.

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N2 - The Swift satellite has enabled us to follow the evolution of gamma-ray burst (GRB) fireballs from the prompt γ-ray emission to the afterglow phase. The early-time X-ray and optical data for GRBs obtained by telescopes aboard the Swift satellite show that the source for prompt γ-ray emission, the emission that heralds these bursts, is short lived, and is distinct from the source for the long-lived afterglow emission that follows the initial burst. Using these data we determine the distance of the γ-ray source from the centre of the explosion. We find this distance to be 1015-1016 cm for most bursts, and show that this is within a factor of about 10 of the radius of the shock heated circumstellar medium (CSM) producing the X-ray photons. Furthermore, using the early γ-ray, X-ray and optical data we show that the prompt gamma-ray emission cannot be produced in internal shocks nor can it be produced in the external shock; in a more general sense γ-ray generation mechanisms based on shock physics have problems explaining the GRB data for ten Swift bursts analyzed in this work. A magnetic field dominated outflow model for GRBs has a number of attractive features, although evidence in its favour is inconclusive. Finally, the X-ray and optical data allow us to provide an upper limit on the density of the CSM of about 10 protons cmr3 at a distance of ~5 × 1016 cm from the centre of explosion.

AB - The Swift satellite has enabled us to follow the evolution of gamma-ray burst (GRB) fireballs from the prompt γ-ray emission to the afterglow phase. The early-time X-ray and optical data for GRBs obtained by telescopes aboard the Swift satellite show that the source for prompt γ-ray emission, the emission that heralds these bursts, is short lived, and is distinct from the source for the long-lived afterglow emission that follows the initial burst. Using these data we determine the distance of the γ-ray source from the centre of the explosion. We find this distance to be 1015-1016 cm for most bursts, and show that this is within a factor of about 10 of the radius of the shock heated circumstellar medium (CSM) producing the X-ray photons. Furthermore, using the early γ-ray, X-ray and optical data we show that the prompt gamma-ray emission cannot be produced in internal shocks nor can it be produced in the external shock; in a more general sense γ-ray generation mechanisms based on shock physics have problems explaining the GRB data for ten Swift bursts analyzed in this work. A magnetic field dominated outflow model for GRBs has a number of attractive features, although evidence in its favour is inconclusive. Finally, the X-ray and optical data allow us to provide an upper limit on the density of the CSM of about 10 protons cmr3 at a distance of ~5 × 1016 cm from the centre of explosion.

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JO - Monthly Notices of the Royal Astronomical Society: Letters

JF - Monthly Notices of the Royal Astronomical Society: Letters

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