Multiwavelength Analysis of the Intriguing GRB 061126: The Reverse Shock Scenario and Magnetization

Multiwavelength Analysis of the Intriguing GRB 061126: The Reverse Shock Scenario and Magnetization

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 ¼ 191 s) with four overlapping peaks in its -ray light curve. The X-ray afterglow, observed...

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Bibliographic Details
Main Authors: Gomboc, A., Kobayashi, S., Guidorzi, C., Melandri, A., Mangano, V., Sbarufatti, B., Mundell, C., Schady, P., Smith, R., Updike, A., Kann, D., Misra, K., Rol, E., Pozanenko, A., Castro-Tirado, A., Anupama, G., Bersier, D., Bode, M., Carter, D., Curran, Peter, Fruchter, A., Graham, J., Hartmann, D., Ibrahimov, M., Levan, A., Monfardini, A., Mottram, C., O’Brien, P., Prema, P., Sahu, D., Steele, I., Tanvir, N., Wiersema, K.
Format: Journal Article
Published: Institute of Physics Publishing, Inc. 2008
Subjects:
cosmology: observations
gamma rays: bursts
Online Access:http://iopscience.iop.org/0004-637X/687/1/443/pdf/74449.web.pdf
http://hdl.handle.net/20.500.11937/39783
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Summary: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 ¼ 191 s) with four overlapping peaks in its -ray light curve. The X-ray afterglow, observed from 26 minutes to20 days after the burst, shows a simple power-law decay with X ¼ 1:290 0:008. Optical observations presentedhere cover the time range from 258 s (Faulkes Telescope North) to 15 days (Gemini North) after the burst; the decayrate of the optical afterglow shows a steep-to-shallow transition (from 1 ¼ 1:48 0:06 to 2 ¼ 0:88 0:03) approximately13 minutes after the burst.We suggest the early, steep component is due to a reverse shock and show thatthe magnetic energy density in the ejecta, expressed as a fraction of the equipartition value, is a few 10 times largerthan in the forward shock in the early afterglow phase. The ejecta might be endowed with primordial magnetic fieldsat the central engine. The optical light curve implies a late-time break at about 1.5 days after the burst, while there is noevidence of the simultaneous break in the X-ray light curve. We model the broadband emission and show that someafterglow characteristics (the steeper decay in X-ray and the shallow spectral index from optical to X-ray) are difficultto explain in the framework of the standard fireball model. This might imply that the X-ray afterglow is due to anadditional emission process, such as late-time central engine activity rather than blast-wave shock emission. Thepossible chromatic break at 1.5 days after the burst would give support to the additional emission scenario.

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