S. Covino, D. Malesani, G. Ghisellini, P. Saracco, G. Tagliaferri, F. Zerbi
(Observ. of Brera, Milan, Italy); S. Di Serego, A. Cimatti, M. Della Valle
(Observ. of Arcetri, Florence, Italy); F. Fiore, G.L. Israel, L. Stella
(Observ. of Monte Porzio, Rome, Italy); M. Vietri (Univ. Rome 3, Italy); N.
Kawai (Tokyo Tech, Japan); D. Lazzati (IoA, Cambridge, UK); S. Ortolani
(Univ. of Padua, Italy); L. Pasquini (ESO, Germany); G. Ricker (MIT, USA);
E. Le Floch, P. Goldoni, F. Mirabel (CEA, France) report:
In GCN 1498 we claimed that the polarization measurements performed by Barth
et al. (GCN 1477) and our group on the GRB 020813 afterglow allow to single
out "the most significant and larger degree of variability ever detected in
the polarization level of a GRB optical afterglow".
However, according to the result of Bersier et al. (astro-ph/0206465) a large
amount of variability in the polarization level could have been present in
GRB 020405 if compared to the polarization level measured again by our own
group (Covino et al., GCN 1431).
In this case, the measurements performed for GRB 020813 are only a
confirmation for the large variability in a short time scale (~24 hours) in
the polarization level of a GRB optical afterglow.
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