%0 Journal Article %A Gorosabel, J. %A Castro-Tirado, A. J. %A Cerón, J. M. C. %A Fruchter, A. S. %A Rhoads, J. %A Rol, E. %A Kaper, L. %A Van Den Heuvel E %A Wijers, R. A. M. J. %A Covino, S. %A Ghisellini, G. %A Saracco, P. %A Tagliaferri, G. %A Zerbi, F. M. %A Lazzati, D. %A Hjorth, J. %A Malesani, D. %A M, Della Valle %A Di Serego Alighieri S %A Fiore, F. %A Israel, G. L. %A Stella, L. %A Fynbo, J. P. U. %A Goldoni, P. %A Le Floc'h E %A Mirabel, F. %A Greiner, J. %A Kawai, N. %A Klose, S. %A Kouveliotou, C. %A Masetti, N. %A Palazzi, E. %A Møller, P. %A Ortolani, S. %A Pian, E. %A Ricker, G. %A Tanvir, N. %A Vietri, M. %A Vreeswijk, P. M. %D 2012 %T GRB 020813: Polarization in the case of a smooth optical decay %U https://figshare.le.ac.uk/articles/journal_contribution/GRB_020813_Polarization_in_the_case_of_a_smooth_optical_decay/10118477 %2 https://figshare.le.ac.uk/ndownloader/files/18235373 %K IR content %X 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. %I University of Leicester