[vsnet-grb-info 350] GRB 020813: addendum to GCN 1498

[GCN Circulars <gcncirc@lheawww.gsfc.nasa.gov>]

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  1502
SUBJECT: GRB 020813: addendum to GCN 1498
DATE:    02/08/17 11:30:50 GMT
FROM:    Stefano Covino at Brera Astronomical Observatory  <covino@merate.mi.astro.it>

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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