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Title: Physics of the GRB 030328 afterglow and its environment
Authors: Maiorano, E.
Masetti, N.
Palazzi, E.
Pian, E.
Amati, L.
Frontera, F.
Nicastro, L.
Maiorano, E.
Pian, E.
Maiorano, E.
Savaglio, S.
Rol, E.
Vreeswijk, P. M.
Price, P. A.
Price, P. A.
Peterson, B. A.
Jelínek, M.
Castro-Tirado, A. J.
De Ugarte Postigo A
Gorosabel, J.
Pandey, S. B.
Andersen, M. I.
Cerón, J. M. C.
Fynbo, J. P. U.
Hjorth, J.
Jensen, B. L.
Frontera, F.
Fruchter, A. S.
Rhoads, J.
Henden, A. A.
Klose, S.
Kouveliotou, C.
Masi, G.
Møller, P.
Ofek, E. O.
Pandey, S. B.
Tanvir, N. R.
Wijers, R. A. M. J.
Van Den Heuvel E. P. J.
First Published: Aug-2006
Publisher: EDP Sciences for European Southern Observatory (ESO)
Citation: Astronomy & Astrophysics, 2006, 455 (2), pp. 423-431
Abstract: Aims.To investigate the physical nature of the afterglow emission. We report on the photometric, spectroscopic and polarimetric observations of the optical afterglow of Gamma-Ray Burst (GRB) 030328 detected by HETE-2. Methods.Photometric, spectroscopic and polarimetric monitoring of the optical afterglow. Results.Photometry, collected at 7 different telescopes, shows that a smoothly broken powerlaw decay, with indices $\alpha_1 = 0.76$ $\pm$ 0.03, $\alpha_2 = 1.50$ $\pm$ 0.07 and a break at $t_{\rm b}$ = 0.48 $\pm$ 0.03 days after the GRB, provides the best fit of the optical afterglow decline. This shape is interpreted as due to collimated emission, for which we determine a jet opening angle $\theta_{\rm jet} \sim$ 3$\fdg$2. An achromatic bump starting around ~0.2 d after the GRB is possibly marginally detected in the optical light curves. Optical spectroscopy shows the presence of two rest-frame ultraviolet metal absorption systems at z = 1.5216 $\pm$ 0.0006 and at z = 1.295 $\pm$ 0.001, the former likely associated with the GRB host galaxy. Analysis of the absorption lines at z = 1.5216 suggests that the host of this GRB may be a Damped Lyman-$\alpha$ Absorber. The optical V-band afterglow appears polarized, with P = (2.4 $\pm$ 0.6)% and $\theta$ = $170^{\circ}$ $\pm$ $7^{\circ}$, suggesting an asymmetric blastwave expansion. An X-ray-to-optical spectral flux distribution of the GRB 030328 afterglow was obtained at 0.78 days after the GRB and fitted using a broken powerlaw, with an optical spectral slope $\beta_{\rm opt} = 0.47$ $\pm$ 0.15, and an X-ray slope $\beta_{\rm X} = 1.0$ $\pm$ 0.2. Conclusions.The discussion of the results in the context of the "fireball model" shows that the preferred scenario for this afterglow is collimated structured jet with fixed opening angle in a homogeneous medium.
DOI Link: 10.1051/0004-6361:20054728
ISSN: 0004-6361
eISSN: 1432-0746
Version: Publisher Version
Status: Peer-reviewed
Type: Journal Article
Rights: Copyright © 2006 ESO. Reproduced with permission from Astronomy & Astrophysics, © ESO.
Appears in Collections:Published Articles, Dept. of Physics and Astronomy

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