[vsnet-grb-info 266] GRB020405: polarimetric observations

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

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  1431
SUBJECT: GRB020405: polarimetric observations
DATE:    02/06/19 10:15:48 GMT
FROM:    Stefano Covino at Brera Astronomical Observatory  <covino@merate.mi.astro.it>

S. Covino, G. Ghisellini, D. Malesani, 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, I); 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, F)  report:


On 2002 April 7.21 and April 8.26 we observed the optical counterpart to

GRB020405. The observations were performed with the ESO VLT-3 (Melipal)
telescope equipped with FORS1 with a Bessel V band filter in the imaging

polarimetry mode. The transient source is clearly detected superposed to
a
bright galaxy. The acquisition images allowed us to derive the magnitude
of
the transient as reported in GCN 1337 and GCN 1345 (Covino et al.).

On April 7.21 (2.1 days after the GRB) we found linear polarization at
the
level of 1.93 +/- 0.33 per cent with position angle 154 +/- 5 degrees
while
on April 8.26 (3.2 days after the GRB) we found linear polarization at
the
level of 1.23 +/- 0.43 per cent with position angle 168 +/- 9 degrees.
Polarization measurements were corrected for any instrumental effect or
measurement bias and the reported polarization degrees and position
angles
are derived from Stokes parameters normalized to the average of the
field
stars.


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