Volume 607, November 2017
|Number of page(s)||5|
|Published online||31 October 2017|
Colour variations in the GRB 120327A afterglow⋆
1 INAF–Osservatorio Astronomico di Brera, via E. Bianchi 36, 23807 Merate (LC), Italy
2 ICRANet-Rio, Centro Brasileiro de Pesquisas Físicas, Rua Dr. Xavier Sigaud 150, Rio de Janeiro, RJ 22290-180, Brazil
3 Max-Planck-Institut für extraterrestrische Physik, Giessenbachstrasse 1, 85748 Garching, Germany
4 Department of Physics, The George Washington University, Washington, DC 20052, USA
5 Instituto de Astrofísica de Andalucía (IAA-CSIC), Glorieta de la Astronomía s/n, 18008 Granada, Spain
6 CEOU/Astronomy Program, Dept. of Physics & Astronomy, Seoul National University, Seoul, 151-742, South Korea
7 Mullard Space Science Laboratory, University College London, Holmbury St Mary, Dorking, Surrey RH5 6NT, UK
8 Okayama Astrophysical Observatory, National Astronomical Observatory of Japan, Asakuchi, Okayama 719-0232, Japan
9 Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, 2100 Copenhagen, Denmark
10 Astrophysics Research Institute, Liverpool JMU, IC2, Liverpool Science Park, 146 Brownlow Hill, Liverpool L3 5RF, UK
11 Department of Physics, University of Bath, Claverton Down, Bath, BA2 7AY, UK
12 Department of Astronomy and Astrophysics, Pennsylvania State University, University Park, PA 16802, USA
13 Dublin Institute for Advanced Studies, 31 Fitzwilliam Place, Dublin 2, Ireland
14 Skynet Robotic Telescope Network, Dep. of Physics and Astronomy, Univ. of North Carolina, Chapel Hill, NC 27599-3255, USA
15 Department of Physics, North Carolina A&T State University, Greensboro, NC 27411, USA
16 Laboratoire Univers et Particules de Montpellier, Université Montpellier, Place Eugène Bataillon, 34095 Montpellier, France
17 INAF–Osservatorio Astronomico di Roma, via Frascati 33, 00078 Monteporzio Catone ( Roma), Italy
18 ASI Science Data Centre, via del Politecnico snc, 00133 Roma, Italy
19 Centre for Astrophysics and Cosmology, University of Nova Gorica, Vipavska 11c, 5270 Ajdovščina, Slovenia
20 Dipartimento di Fisica, Universitá di Ferrara, via Saragat 1, 44100 Ferrara, Italy
21 Ishigakijima Astronomical Observatory, NAO of Japan, 1024-1, Arakawa, Ishigaki, Okinawa 907-0024, Japan
22 University College Dublin, School of Physics UCD, Belfield, Dublin 4, Ireland
23 Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, 1000 Ljubljana, Slovenia
24 Astronomical Institute, Czech Academy of Sciences, (ASU CAS), Ondřejov, Czech Republic
25 INAF–IASF Milano, via E. Bassini 15, 20133 Milano, Italy
26 GEPI,Observatoire de Paris, CNRS, Univ. Paris Diderot, 5 place Jules Janssen, 92190 Meudon, France
27 Korea Astronomy and Space Science Institute, Daejeon 34055, Korea
Received: 11 August 2017
Accepted: 21 September 2017
Aims. We present a comprehensive temporal and spectral analysis of the long Swift GRB 120327A afterglow data to investigate possible causes of the observed early-time colour variations.
Methods. We collected data from various instruments and telescopes in X-ray, ultraviolet, optical, and near-infrared bands, and determined the shapes of the afterglow early-time light curves. We studied the overall temporal behaviour and the spectral energy distributions from early to late times.
Results. The ultraviolet, optical, and near-infrared light curves can be modelled with a single power-law component between 200 and 2 × 104 s after the burst event. The X-ray light curve shows a canonical steep-shallow-steep behaviour that is typical of long gamma-ray bursts. At early times a colour variation is observed in the ultraviolet/optical bands, while at very late times a hint of a re-brightening is visible. The observed early-time colour change can be explained as a variation in the intrinsic optical spectral index, rather than an evolution of the optical extinction.
Key words: gamma-ray burst: individual: GRB 120327A / dust, extinction
Table 2 is only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (188.8.131.52) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/607/A29
© ESO, 2017
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