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Title: GRB 020813: Polarization in the case of a smooth optical decay
Authors: Gorosabel, J.
Castro-Tirado, A. J.
Gorosabel, J.
Cerón, J. M. C.
Fruchter, A. S.
Rhoads, J.
Rol, E.
Kaper, L.
Van Den Heuvel E
Wijers, R. A. M. J.
Covino, S.
Ghisellini, G.
Saracco, P.
Tagliaferri, G.
Zerbi, F. M.
Lazzati, D.
Hjorth, J.
Malesani, D.
Della Valle M
Di Serego Alighieri S
Fiore, F.
Israel, G. L.
Stella, L.
Fynbo, J. P. U.
Goldoni, P.
Le Floc'h E
Mirabel, F.
Greiner, J.
Kawai, N.
Klose, S.
Kouveliotou, C.
Masetti, N.
Palazzi, E.
Møller, P.
Ortolani, S.
Pian, E.
Ricker, G.
Tanvir, N.
Vietri, M.
Vreeswijk, P. M.
First Published: Jul-2004
Publisher: EDP Sciences for European Southern Observatory (ESO)
Citation: Astronomy & Astrophysics, 2004, 422 (1), pp. 113-119
Abstract: We present the results of a VLT polarimetric monitoring campaign of the GRB 020813 optical afterglow carried out in three nights, from 0.88 to 4.20 days after the gamma-ray event. The mean values of the degree of linear polarization ( P) and its position angle ( $\theta$) resulting from our campaign are $\langle P\rangle=1.18 \pm 0.10 \%$ and $\langle \theta\rangle = 148.7^{\circ} \pm 2.3^{\circ}$ , after correcting for Galactic interstellar polarization. Our VLT data set is most naturally described by a constant degree of linear polarization and position angle, nonetheless a slow $\theta$ evolution cannot be entirely ruled out by our data. The VLT monitoring campaign did not reveal either a significant $\theta$ rotation respect to the Keck spectropolarimetric observations performed ~0.25 days after the GRB (Barth et al. 2003). However, $\langle P\rangle $ is a factor of two lower than the polarization degree measured from Keck. Additionally, the VLT polarization data allowed us to construct an accurate V-band light curve. The V-band photometric data revealed a smooth light curve with a break located between the last Keck and our first VLT polarimetric measurement, $0.33 < t_{{\rm break}, V} < 0.88$ days after the GRB. The typical magnitude fluctuations of the VLT V-band lightcurve are 0.003 mag, 0.010 mag and 0.016 mag for our three observing nights, respectively. We speculate that the stability of $\theta$ might be related to the smoothness of the light curve.
DOI Link: 10.1051/0004-6361:20034409
ISSN: 0004-6361
Version: Publisher Version
Status: Peer-reviewed
Type: Journal Article
Rights: Copyright © 2004 ESO. Reproduced with permission from Astronomy & Astrophysics, © ESO.
Appears in Collections:Published Articles, Dept. of Physics and Astronomy

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