Infrared/optical-X-ray simultaneous observations of X-ray flares in GRB 071112C and GRB 080506

Uehara Takeshi

Uemura Makoto

Kawabata Koji S

Fukazawa Yasushi

Yamazaki Ryo

Arai Akira

Sasada Mahito

Ohsugi Takashi

Mizuno Tsunefumi

Takahashi Hiromitsu

Katagiri Hideaki

Yamashita Takuya

Ohno Masanori

Sato Goro

Sato Shuji

Kino Masaru

Astronomy & Astrophysics

Aims. We investigate the origin of short X-ray flares which are occasionally observed in early stages of afterglows of gamma-ray bursts (GRBs).

Methods. We observed two Swift events, GRB 071112C and GRB 080506, before the start of X-ray flares in the optical and near-infrared (NIR) bands with the 1.5-m Kanata telescope. In conjunction with published X-ray and optical data, we analyzed densely sampled light curves of the early afterglows and spectral energy distributions (SEDs) in the NIR-X-ray ranges.

Results. We found that the SEDs had a break between the optical and X-ray bands in the normal decay phases of both GRBs regardless of the model for the correction of the interstellar extinction in host galaxies of GRBs. In the X-ray flares, X-ray flux increased by 3 and 15 times in the case of GRB 071112C and 080506, respectively, and the X-ray spectra became harder than those in the normal decay phases. No significant variation in the optical-NIR range was detected together with the X-ray flares.

Conclusions. These results suggest that the X-ray flares were associated with either late internal shocks or external shocks from two-component jets.

gamma-ray burst

individual

GRB 071112C – gamma-ray burst

individual

GRB 080506

Astronomy. Space sciences [ 440 ]

eng

EDP Sciences S A

Copyright (c) 2010 The European Southern Observatory

[ISSN] 0004-6361

[DOI] 10.1051/0004-6361/201014272

[NCID] AA00553195

[DOI] http://dx.doi.org/10.1051/0004-6361/201014272