[vsnet-grb-info 265] GRB 020531, simultaneous optical observations

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

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  1430
SUBJECT: GRB 020531, simultaneous optical observations
DATE:    02/06/14 00:21:53 GMT
FROM:    Alberto Castro-Tirado at LAEFF-INTA  <ajct@laeff.esa.es>

A. J. Castro-Tirado (IAA-CSIC and LAEFF-INTA), J. M. Castro Cerón (ROA),
A. de Ugarte Postigo (UCM), R. Hudec, M. Jélinek (ASU),
M. Bernas, P. Páta (CVUT) and J. Á. Berná (Univ. de Alicante)
on behalf of the BOOTES team,

report:

"We have obtained about 120 unfiltred exposures (120-s each) under
poor metereological conditions covering the possible short/hard GRB
020531 error box (HETE trigger 7688 at To = 00:26:18 UT, GCN 1399)
during the period  20:15 UT 30 May 2002 - 02:15 UT 31 May 2002
(i.e. between 4.19-hours before the trigger and 1.82-hours after
the trigger) with the wide-field camera of BOOTES-1
(http://www.laeff.esa.es/BOOTES).

After a visual inspection of the IPN error box (GCN 1407) in all frames,
we do not find evidence of optical emission, in particular simultaneously
to the burst itself. We derive the following upper limits :

   Date of mid-exposure         Limiting magnitude    Sky conditions
-----------------------------   ------------------    --------------
May 30, 22:18 UT  (To - 2 hr)        10.5                thin cirrus
May 31, 00:26 UT     (To)             8.0                thick cirrus
May 31, 00:56 UT (T0 + 0.5 hr)        8.0                thick cirrus


The fact that no optical afterglow has been found for this GRB
(cf. GCN 1403, 1404, 1405, 1406, 1408, 1416, 1421, 1427) supports
the idea that most short GRBs might occur in a low density medium.
This would be also implied by the BOOTES detection of an optical
transient (OT) following the short/hard GRB 000313, if both, the OT
and the GRB are related (Castro-Tirado et al. 2002, submitted to A&A,
astro-ph/0206201)."

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