Multiwavelength analysis of the intriguing GRB 061126

The reverse shock scenario and magnetization

A. Gomboc, S. Kobayashi, C. Guidorzi, A. Melandri, V. Mangano, B. Sbarufatti, C. G. Mundell, P. Schady, R. J. Smith, A. C. Updike, D. A. Kann, K. Misra, E. Rol, A. Pozanenko, A. J. Castro-Tirado, G. C. Anupama, D. Bersier, M. F. Bode, D. Carter, P. Curran & 13 others A. Fruchter, J. Graham, D. H. Hartmann, M. Ibrahimov, A. Levan, A. Monfardini, C. J. Mottram, P. T. O'Brien, P. Prema, D. K. Sahu, I. A. Steele, N. R. Tanvir, K. Wiersema

Research output: Contribution to journalArticle

61 Citations (Scopus)

Abstract

We present a detailed study of the prompt and afterglow emission from Swift GRB 061126 using BAT, XRT, UVOT data and multicolor optical imaging from 10 ground-based telescopes. GRB 061126 was a long burst (T90 = 191 s) with four overlapping peaks in its γ-ray light curve. The X-ray afterglow, observed from 26 minutes to 20 days after the burst, shows a simple power-law decay with αX = 1.290 ± 0.008. Optical observations presented here cover the time range from 258 s (Faulkes Telescope North) to 15 days (Gemini North) after the burst; the decay rate of the optical afterglow shows a steep-to-shallow transition (from α1 = 1.48 ± 0:06 to α2 = 0.88 ± 0.03) approximately 13 minutes after the burst. We suggest the early, steep component is due to a reverse shock and show that the magnetic energy density in the ejecta, expressed as a fraction of the equipartition value, is a few 10 times larger than in the forward shock in the early afterglow phase. The ejecta might be endowed with primordial magnetic fields at the central engine. The optical light curve implies a late-time break at about 1.5 days after the burst, while there is no evidence of the simultaneous break in the X-ray light curve. We model the broadband emission and show that some afterglow characteristics (the steeper decay in X-ray and the shallow spectral index from optical to X-ray) are difficult to explain in the framework of the standard fireball model. This might imply that the X-ray afterglow is due to an additional emission process, such as late-time central engine activity rather than blast-wave shock emission. The possible chromatic break at 1.5 days after the burst would give support to the additional emission scenario.

Original languageEnglish
Pages (from-to)443-455
Number of pages13
JournalAstrophysical Journal
Volume687
Issue number1
DOIs
Publication statusPublished - 1 Nov 2008

Fingerprint

afterglows
magnetization
bursts
shock
light curve
ejecta
x rays
engine
engines
telescopes
shock wave
fireballs
decay
blasts
power law
decay rates
analysis
shock waves
magnetic field
flux density

Keywords

  • Cosmology: Observations
  • Gamma rays: Bursts

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Gomboc, A., Kobayashi, S., Guidorzi, C., Melandri, A., Mangano, V., Sbarufatti, B., ... Wiersema, K. (2008). Multiwavelength analysis of the intriguing GRB 061126: The reverse shock scenario and magnetization. Astrophysical Journal, 687(1), 443-455. https://doi.org/10.1086/592062, https://doi.org/10.1086/592062

Multiwavelength analysis of the intriguing GRB 061126 : The reverse shock scenario and magnetization. / Gomboc, A.; Kobayashi, S.; Guidorzi, C.; Melandri, A.; Mangano, V.; Sbarufatti, B.; Mundell, C. G.; Schady, P.; Smith, R. J.; Updike, A. C.; Kann, D. A.; Misra, K.; Rol, E.; Pozanenko, A.; Castro-Tirado, A. J.; Anupama, G. C.; Bersier, D.; Bode, M. F.; Carter, D.; Curran, P.; Fruchter, A.; Graham, J.; Hartmann, D. H.; Ibrahimov, M.; Levan, A.; Monfardini, A.; Mottram, C. J.; O'Brien, P. T.; Prema, P.; Sahu, D. K.; Steele, I. A.; Tanvir, N. R.; Wiersema, K.

In: Astrophysical Journal, Vol. 687, No. 1, 01.11.2008, p. 443-455.

Research output: Contribution to journalArticle

Gomboc, A, Kobayashi, S, Guidorzi, C, Melandri, A, Mangano, V, Sbarufatti, B, Mundell, CG, Schady, P, Smith, RJ, Updike, AC, Kann, DA, Misra, K, Rol, E, Pozanenko, A, Castro-Tirado, AJ, Anupama, GC, Bersier, D, Bode, MF, Carter, D, Curran, P, Fruchter, A, Graham, J, Hartmann, DH, Ibrahimov, M, Levan, A, Monfardini, A, Mottram, CJ, O'Brien, PT, Prema, P, Sahu, DK, Steele, IA, Tanvir, NR & Wiersema, K 2008, 'Multiwavelength analysis of the intriguing GRB 061126: The reverse shock scenario and magnetization', Astrophysical Journal, vol. 687, no. 1, pp. 443-455. https://doi.org/10.1086/592062, https://doi.org/10.1086/592062
Gomboc, A. ; Kobayashi, S. ; Guidorzi, C. ; Melandri, A. ; Mangano, V. ; Sbarufatti, B. ; Mundell, C. G. ; Schady, P. ; Smith, R. J. ; Updike, A. C. ; Kann, D. A. ; Misra, K. ; Rol, E. ; Pozanenko, A. ; Castro-Tirado, A. J. ; Anupama, G. C. ; Bersier, D. ; Bode, M. F. ; Carter, D. ; Curran, P. ; Fruchter, A. ; Graham, J. ; Hartmann, D. H. ; Ibrahimov, M. ; Levan, A. ; Monfardini, A. ; Mottram, C. J. ; O'Brien, P. T. ; Prema, P. ; Sahu, D. K. ; Steele, I. A. ; Tanvir, N. R. ; Wiersema, K. / Multiwavelength analysis of the intriguing GRB 061126 : The reverse shock scenario and magnetization. In: Astrophysical Journal. 2008 ; Vol. 687, No. 1. pp. 443-455.
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AU - Gomboc, A.

AU - Kobayashi, S.

AU - Guidorzi, C.

AU - Melandri, A.

AU - Mangano, V.

AU - Sbarufatti, B.

AU - Mundell, C. G.

AU - Schady, P.

AU - Smith, R. J.

AU - Updike, A. C.

AU - Kann, D. A.

AU - Misra, K.

AU - Rol, E.

AU - Pozanenko, A.

AU - Castro-Tirado, A. J.

AU - Anupama, G. C.

AU - Bersier, D.

AU - Bode, M. F.

AU - Carter, D.

AU - Curran, P.

AU - Fruchter, A.

AU - Graham, J.

AU - Hartmann, D. H.

AU - Ibrahimov, M.

AU - Levan, A.

AU - Monfardini, A.

AU - Mottram, C. J.

AU - O'Brien, P. T.

AU - Prema, P.

AU - Sahu, D. K.

AU - Steele, I. A.

AU - Tanvir, N. R.

AU - Wiersema, K.

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N2 - We present a detailed study of the prompt and afterglow emission from Swift GRB 061126 using BAT, XRT, UVOT data and multicolor optical imaging from 10 ground-based telescopes. GRB 061126 was a long burst (T90 = 191 s) with four overlapping peaks in its γ-ray light curve. The X-ray afterglow, observed from 26 minutes to 20 days after the burst, shows a simple power-law decay with αX = 1.290 ± 0.008. Optical observations presented here cover the time range from 258 s (Faulkes Telescope North) to 15 days (Gemini North) after the burst; the decay rate of the optical afterglow shows a steep-to-shallow transition (from α1 = 1.48 ± 0:06 to α2 = 0.88 ± 0.03) approximately 13 minutes after the burst. We suggest the early, steep component is due to a reverse shock and show that the magnetic energy density in the ejecta, expressed as a fraction of the equipartition value, is a few 10 times larger than in the forward shock in the early afterglow phase. The ejecta might be endowed with primordial magnetic fields at the central engine. The optical light curve implies a late-time break at about 1.5 days after the burst, while there is no evidence of the simultaneous break in the X-ray light curve. We model the broadband emission and show that some afterglow characteristics (the steeper decay in X-ray and the shallow spectral index from optical to X-ray) are difficult to explain in the framework of the standard fireball model. This might imply that the X-ray afterglow is due to an additional emission process, such as late-time central engine activity rather than blast-wave shock emission. The possible chromatic break at 1.5 days after the burst would give support to the additional emission scenario.

AB - We present a detailed study of the prompt and afterglow emission from Swift GRB 061126 using BAT, XRT, UVOT data and multicolor optical imaging from 10 ground-based telescopes. GRB 061126 was a long burst (T90 = 191 s) with four overlapping peaks in its γ-ray light curve. The X-ray afterglow, observed from 26 minutes to 20 days after the burst, shows a simple power-law decay with αX = 1.290 ± 0.008. Optical observations presented here cover the time range from 258 s (Faulkes Telescope North) to 15 days (Gemini North) after the burst; the decay rate of the optical afterglow shows a steep-to-shallow transition (from α1 = 1.48 ± 0:06 to α2 = 0.88 ± 0.03) approximately 13 minutes after the burst. We suggest the early, steep component is due to a reverse shock and show that the magnetic energy density in the ejecta, expressed as a fraction of the equipartition value, is a few 10 times larger than in the forward shock in the early afterglow phase. The ejecta might be endowed with primordial magnetic fields at the central engine. The optical light curve implies a late-time break at about 1.5 days after the burst, while there is no evidence of the simultaneous break in the X-ray light curve. We model the broadband emission and show that some afterglow characteristics (the steeper decay in X-ray and the shallow spectral index from optical to X-ray) are difficult to explain in the framework of the standard fireball model. This might imply that the X-ray afterglow is due to an additional emission process, such as late-time central engine activity rather than blast-wave shock emission. The possible chromatic break at 1.5 days after the burst would give support to the additional emission scenario.

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KW - Gamma rays: Bursts

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