GCN Circular 1502

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
Not found
 
 
 we claimed that the polarization measurements performed by Barth 
et al. (GCN 1477
Not found
 
 
) 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
Not found
 
 
).


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.




This message may be cited.