Evidence for a canonical gamma-ray burst afterglow light curve in the Swift XRT data

A. Nousek, C. Kouveliotou, D. Grupe, K. L. Page, J. Granot, E. Ramirez-Ruiz, S. K. Patel, D. N. Burrows, V. Mangano, S. Barthelmy, A. P. Beardmore, S. Campana, M. Capalbi, G. Chincarini, G. Cusumano, A. D. Falcone, N. Gehrels, P. Giommi, M. R. Goad, O. GodetC. P. Hurkett, J. A. Kennea, A. Moretti, P. T. O'Brien, J. P. Osborne, P. Romand, G. Tagliaferri, A. A. Wells

Research output: Contribution to journalArticle

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Abstract

We present new observations of the early X-ray afterglows of the first 27 gamma-ray bursts (GRBs) well observed by the Swift X-Ray Telescope (XRT). The early X-ray afterglows show a canonical behavior, where the light curve broadly consists of three distinct power-law segments: (1) an initial very steep decay (∝t-α with 3 ≲ α1 ≲ 5), followed by (2) a very shallow decay (0.5 ≲ α2 ≲ 1.0), and finally (3) a somewhat steeper decay (1 ≲ α3 ≲ 1.5). These power-law segments are separated by two corresponding break times, tbreak,1 ≲ 500 s and 103 s ≲ t break,2 ≲ 104 s. On top of this canonical behavior, many events have superimposed X-ray flares, which are most likely caused by internal shocks due to long-lasting sporadic activity of the central engine, up to several hours after the GRB. We find that the initial steep decay is consistent with it being the tail of the prompt emission, from photons that are radiated at large angles relative to our line of sight. The first break in the light curve (tbreak,1) takes place when the forward shock emission becomes dominant, with the intermediate shallow flux decay (α 2) likely caused by the continuous energy injection into the external shock. When this energy injection stops, a second break is then observed in the light curve (tbreak,2). This energy injection increases the energy of the afterglow shock by at least a factor of f ≳ 4 and augments the already severe requirements for the efficiency of the prompt gamma-ray emission.

Original languageEnglish (US)
Pages (from-to)389-400
Number of pages12
JournalAstrophysical Journal
Volume642
Issue number1 I
DOIs
StatePublished - May 1 2006

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afterglows
gamma ray bursts
light curve
telescopes
shock
decay
energy
injection
power law
x rays
engine
line of sight
flares
engines
gamma rays
requirements
photons

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Nousek, A., Kouveliotou, C., Grupe, D., Page, K. L., Granot, J., Ramirez-Ruiz, E., ... Wells, A. A. (2006). Evidence for a canonical gamma-ray burst afterglow light curve in the Swift XRT data. Astrophysical Journal, 642(1 I), 389-400. https://doi.org/10.1086/500724
Nousek, A. ; Kouveliotou, C. ; Grupe, D. ; Page, K. L. ; Granot, J. ; Ramirez-Ruiz, E. ; Patel, S. K. ; Burrows, D. N. ; Mangano, V. ; Barthelmy, S. ; Beardmore, A. P. ; Campana, S. ; Capalbi, M. ; Chincarini, G. ; Cusumano, G. ; Falcone, A. D. ; Gehrels, N. ; Giommi, P. ; Goad, M. R. ; Godet, O. ; Hurkett, C. P. ; Kennea, J. A. ; Moretti, A. ; O'Brien, P. T. ; Osborne, J. P. ; Romand, P. ; Tagliaferri, G. ; Wells, A. A. / Evidence for a canonical gamma-ray burst afterglow light curve in the Swift XRT data. In: Astrophysical Journal. 2006 ; Vol. 642, No. 1 I. pp. 389-400.
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Nousek, A, Kouveliotou, C, Grupe, D, Page, KL, Granot, J, Ramirez-Ruiz, E, Patel, SK, Burrows, DN, Mangano, V, Barthelmy, S, Beardmore, AP, Campana, S, Capalbi, M, Chincarini, G, Cusumano, G, Falcone, AD, Gehrels, N, Giommi, P, Goad, MR, Godet, O, Hurkett, CP, Kennea, JA, Moretti, A, O'Brien, PT, Osborne, JP, Romand, P, Tagliaferri, G & Wells, AA 2006, 'Evidence for a canonical gamma-ray burst afterglow light curve in the Swift XRT data', Astrophysical Journal, vol. 642, no. 1 I, pp. 389-400. https://doi.org/10.1086/500724

Evidence for a canonical gamma-ray burst afterglow light curve in the Swift XRT data. / Nousek, A.; Kouveliotou, C.; Grupe, D.; Page, K. L.; Granot, J.; Ramirez-Ruiz, E.; Patel, S. K.; Burrows, D. N.; Mangano, V.; Barthelmy, S.; Beardmore, A. P.; Campana, S.; Capalbi, M.; Chincarini, G.; Cusumano, G.; Falcone, A. D.; Gehrels, N.; Giommi, P.; Goad, M. R.; Godet, O.; Hurkett, C. P.; Kennea, J. A.; Moretti, A.; O'Brien, P. T.; Osborne, J. P.; Romand, P.; Tagliaferri, G.; Wells, A. A.

In: Astrophysical Journal, Vol. 642, No. 1 I, 01.05.2006, p. 389-400.

Research output: Contribution to journalArticle

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T1 - Evidence for a canonical gamma-ray burst afterglow light curve in the Swift XRT data

AU - Nousek, A.

AU - Kouveliotou, C.

AU - Grupe, D.

AU - Page, K. L.

AU - Granot, J.

AU - Ramirez-Ruiz, E.

AU - Patel, S. K.

AU - Burrows, D. N.

AU - Mangano, V.

AU - Barthelmy, S.

AU - Beardmore, A. P.

AU - Campana, S.

AU - Capalbi, M.

AU - Chincarini, G.

AU - Cusumano, G.

AU - Falcone, A. D.

AU - Gehrels, N.

AU - Giommi, P.

AU - Goad, M. R.

AU - Godet, O.

AU - Hurkett, C. P.

AU - Kennea, J. A.

AU - Moretti, A.

AU - O'Brien, P. T.

AU - Osborne, J. P.

AU - Romand, P.

AU - Tagliaferri, G.

AU - Wells, A. A.

PY - 2006/5/1

Y1 - 2006/5/1

N2 - We present new observations of the early X-ray afterglows of the first 27 gamma-ray bursts (GRBs) well observed by the Swift X-Ray Telescope (XRT). The early X-ray afterglows show a canonical behavior, where the light curve broadly consists of three distinct power-law segments: (1) an initial very steep decay (∝t-α with 3 ≲ α1 ≲ 5), followed by (2) a very shallow decay (0.5 ≲ α2 ≲ 1.0), and finally (3) a somewhat steeper decay (1 ≲ α3 ≲ 1.5). These power-law segments are separated by two corresponding break times, tbreak,1 ≲ 500 s and 103 s ≲ t break,2 ≲ 104 s. On top of this canonical behavior, many events have superimposed X-ray flares, which are most likely caused by internal shocks due to long-lasting sporadic activity of the central engine, up to several hours after the GRB. We find that the initial steep decay is consistent with it being the tail of the prompt emission, from photons that are radiated at large angles relative to our line of sight. The first break in the light curve (tbreak,1) takes place when the forward shock emission becomes dominant, with the intermediate shallow flux decay (α 2) likely caused by the continuous energy injection into the external shock. When this energy injection stops, a second break is then observed in the light curve (tbreak,2). This energy injection increases the energy of the afterglow shock by at least a factor of f ≳ 4 and augments the already severe requirements for the efficiency of the prompt gamma-ray emission.

AB - We present new observations of the early X-ray afterglows of the first 27 gamma-ray bursts (GRBs) well observed by the Swift X-Ray Telescope (XRT). The early X-ray afterglows show a canonical behavior, where the light curve broadly consists of three distinct power-law segments: (1) an initial very steep decay (∝t-α with 3 ≲ α1 ≲ 5), followed by (2) a very shallow decay (0.5 ≲ α2 ≲ 1.0), and finally (3) a somewhat steeper decay (1 ≲ α3 ≲ 1.5). These power-law segments are separated by two corresponding break times, tbreak,1 ≲ 500 s and 103 s ≲ t break,2 ≲ 104 s. On top of this canonical behavior, many events have superimposed X-ray flares, which are most likely caused by internal shocks due to long-lasting sporadic activity of the central engine, up to several hours after the GRB. We find that the initial steep decay is consistent with it being the tail of the prompt emission, from photons that are radiated at large angles relative to our line of sight. The first break in the light curve (tbreak,1) takes place when the forward shock emission becomes dominant, with the intermediate shallow flux decay (α 2) likely caused by the continuous energy injection into the external shock. When this energy injection stops, a second break is then observed in the light curve (tbreak,2). This energy injection increases the energy of the afterglow shock by at least a factor of f ≳ 4 and augments the already severe requirements for the efficiency of the prompt gamma-ray emission.

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Nousek A, Kouveliotou C, Grupe D, Page KL, Granot J, Ramirez-Ruiz E et al. Evidence for a canonical gamma-ray burst afterglow light curve in the Swift XRT data. Astrophysical Journal. 2006 May 1;642(1 I):389-400. https://doi.org/10.1086/500724