Volume 572, December 2014
|Number of page(s)||7|
|Published online||27 November 2014|
The nature of the late achromatic bump in GRB 120326A
INAF – Osservatorio Astronomico Brera,
via E. Bianchi 46, 23807
Merate ( LC), Italy
2 ARI – Liverpool John Moores University, IC2 Liverpool Science Park, 146 Brownlow Hill, Liverpool, L3 5RF, UK
3 Dipartimento di Fisica e Scienza della Terra, via Saragat 1, 44122 Ferrara, Italy
4 Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, 1000 Ljubljana, Slovenia
5 Črni Vrh Observatory, Predgriže 29A, 5274 Črni Vrh nad Idrijo, Slovenia
6 Taurus Hill Observatory, Härkämäentie 88, 79480 Kangaslampi, Finland
7 Okayama Astrophysical Observatory – NAOJ, 3037-5 Honjo, Kamogata, Asakuchi, 719-0232 Okayama, Japan
8 Department of Astronomy, University of California, Berkeley, CA 94720-3411, USA
9 Osservatorio Astronomico Bassano Bresciano, via San Michele 4, 25020 Bassano Bresciano ( BS), Italy
10 Osservatorio Astronomico di Cima Rest, via Rest, 25080 Magasa ( BS), Italy
11 Ishigakijima Astronomical Observatory – NAOJ, 1024-1, Arakawa, Ishigaki, 907-0024 Okinawa, Japan
12 Department of Physics, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, 152-8551 Tokyo, Japan
Received: 4 June 2014
Accepted: 22 September 2014
The long Swift gamma-ray burst GRB 120326A at redshift z = 1.798 exhibited a multi-band light-curve with a striking feature: a late-time, long-lasting achromatic rebrightening that is rarely seen in such events. Peaking in optical and X-ray bands ~35 ks (~12.5 ks in the GRB rest frame) after the 70 s GRB prompt burst, the feature brightened nearly two orders of magnitude above the underlying optical power-law decay. By modelling the multi-wavelength light-curves, we investigated possible causes of the rebrightening in the context of the standard fireball model. We excluded a range of scenarios for the origin of this feature: reverse-shock flash, late-time forward-shock peak caused by the passage of the brightest synchrotron frequency through the optical band, late central engine optical or X-ray flares, interaction between the expanding blast wave and a density enhancement in the circumburst medium, and gravitational microlensing. Instead we conclude that the achromatic rebrightening may be caused by a refreshed forward shock or a geometrical effect. In addition, we identify an additional component after the end of the prompt emission, which shapes the observed X-ray and optical light-curves differently, and which rules out a single overall emission component to explain the observed early-time emission.
Key words: gamma-ray burst: general / gamma-ray burst: individual: GRB 120326A
© ESO, 2014
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.