Optical behavior of GRB 061121 around its X-Ray shallow decay phase
Abstract
Aims: We report on a detailed study of the optical afterglow of GRB 061121 with our original time-series photometric data. Along with our optical observations and public X-ray data, we discuss the origin of its optical and X-ray afterglows.
Methods: We observed the optical afterglow of Swift burst GRB 061121 with the Kanata 1.5-m telescope at Higashi-Hiroshima Observatory. Our observation covers a period just after an X-ray plateau phase. We also performed deep imaging with the Subaru telescope in 2010 in order to estimate the contamination by the host galaxy.
Results: In the light curve, we find that the optical afterglow also exhibited a break as in the X-ray afterglow. However, our observation suggests a possible hump structure or a flattening period before the optical break in the light curve. There is no sign of such a hump in the X-ray light curve.
Conclusions: This implies that the optical emitting region was distinct from the X-ray one. The hump in the optical light curve was possibly caused by a passage with the typical frequency of synchrotron emission from another forward shock distinct from the early afterglow. The observed decay and spectral indices are inconsistent with the standard synchrotron-shock model. As a results, the observation requires a change in microphysical parameters in the shock region or prior activity by the central engine. Alternatively, the emission during the shallow decay phase may be a composition of two forward shock emissions, as indicated by the hump structure in the light curve.
- Publication:
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Astronomy and Astrophysics
- Pub Date:
- February 2011
- DOI:
- 10.1051/0004-6361/201015911
- arXiv:
- arXiv:1011.2616
- Bibcode:
- 2011A&A...526A..92U
- Keywords:
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- gamma-ray burst: general;
- Astrophysics - Cosmology and Nongalactic Astrophysics
- E-Print:
- 8 pages, including 4 figures and 2 tables. Accepted to A&