Volume 462, Number 3, February II 2007
|Page(s)||L57 - L60|
|Published online||18 December 2006|
Letter to the Editor
A likely off-axis event with an intense energy injection
Instituto de Astrofísica de Andalucía (IAA-CSIC), Apartado de Correos 3004, 18080 Granada, Spain e-mail: firstname.lastname@example.org
2 Special Astrophysical Observatory, Nizhnij Arkhyz, Zelenchokskaya, Karachaevo-Cherkesia, 369167 Russia
3 Science Institute, University of Iceland, Dunhaga 3, 107 Reykjavík, Iceland
4 Nikolaev State University, Nikolska 24, 54030, Nikolaev, Ukraine
5 Dpto. de Física (EPS), Universidad de Jaén, 23071 Jaén, Spain
6 Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, 2100 Copenhagen, Denmark
7 Astrophysics Research Inst., Liverpool John Moores Univ., Twelve Quays House, Egerton Wharf, Birkenhead, CH41 1LD, UK
8 The UCL Mullard Space Science Laboratory, Holmbury St. Mary, Dorking, Surrey, RH5 6NT, UK
9 Institut de Radio Astronomie Millimétrique (IRAM), 300 rue de la Piscine, 38406 Saint-Martin d'Hères, France
10 Institute of Astronomy, National Central University, Chung-Li 32054, Taiwan, PR China
11 Institute for Physics and Chemical Research (RIKEN), Wako, Saitama 351-0198, Japan
12 Tokyo Institute of Technology, Ookayama, Meguro, Tokyo 152-8550, Japan
13 Department of Astronomy and Earth Sciences, Tokyo Gakugei University, Koganei, Tokyo 184, Japan
14 Kiso Observatory, Institute of Astronomy, University of Tokyo, Mitake-mura, Kiso-gun, Nagano 397-0101, Japan
15 Japan Aerospace Exploration Agency, Institute of Space and Astronautical Science, Sagamihara, Kanagawa 229-8510, Japan
16 Saitama University, Sakura-ku, Saitama 338-8570, Japan
17 TÜBITAK National Observatory, Akdeniz Üniversitesi, 07058, Antalya, Turkey
18 Akdeniz University, Physics Department, 07058 Antalya, Turkey
19 Middle East Technical University, Physics Department, Inonu Bulvari, Ankara, 06531, Turkey
20 Departments of Astronomy, Kazan State University, Kremlevskaya Str., 18, Kazan, 420008, Russia
21 Academy of Sciences of Tatarstan, Bauman Str., 20, Kazan, 420111, Russia
22 Space Research Institute (IKI), 84/32 Profsoyuznaya, Moscow, 117997, Russia
23 Raman Research Institute, Bangalore 560 080, India
24 National Centre for Radio Astrophysics, Ganeshkhind, Pune, 411007, India
Accepted: 14 December 2006
Aims.Understand the shape and implications of the multiband ligth curve of GRB 050408, an X-ray rich (XRR) burst.
Methods.We present a multiband optical light curve, covering the time from the onset of the γ-ray event to several months after, when we only detect the host galaxy. Together with X-ray, millimetre and radio observations we compile what, to our knowledge, is the most complete multiband coverage of an XRR burst afterglow to date.
Results.The optical and X-ray light curve is characterised by an early flattening and an intense bump peaking around 6 days after the burst onset. We explain the former by an off-axis viewed jet, in agreement with the predictions made for XRR by some models, and the latter with an energy injection equivalent in intensity to the initial shock. The analysis of the spectral flux distribution reveals an extinction compatible with a low chemical enrichment surrounding the burst. Together with the detection of an underlying starburst host galaxy we can strengthen the link between XRR and classical long-duration bursts.
Key words: gamma rays: bursts / techniques: photometric
© ESO, 2007
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