[vsnet-grb-info 491] XRF 020903: flattening of the optical light curve.

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

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  1631
SUBJECT: XRF 020903: flattening of the optical light curve.
DATE:    02/10/13 09:51:48 GMT
FROM:    Javier Gorosabel at LAEFF-INTA, Madrid  <jgu@laeff.esa.es>

J. Gorosabel (IAA-CSIC), J. Hjorth, H. Pedersen, 
B.L. Jensen (Univ of Copenhagen), J.P.U. Fynbo (Univ. of Aarhus),
M. Andersen (AIP Potsdam), J.M. Castro Cerón (ROA, San Fernando), 
A.J. Castro-Tirado (IAA-CSIC) report:

We have imaged the transient source present in the field of XRF 020903
(GCN 1530, GCN 1554) with the 1.54-m Danish Telescope around Oct 10.2
UT, yielding the following preliminary BVR-band magnitudes:

    B = 21.89 +/- 0.15
    V = 21.07 +/- 0.12
    R = 20.54 +/- 0.12

The observations we carried out with a mean seeing of 1". The 
zeropoint is based on the calibration given in GCN 1571. These
magnitudes agree with the ones measured on Oct 1.9 UT for the
transient source (GCN 1563). 

The source seems slightly elongated in the North-East direction
at can be seen in at:

http://www.dsri.dk/~jgu/grb020903/FCs/grb020903.R1.gif
http://www.dsri.dk/~jgu/grb020903/FCs/grb020903.R2.gif

Thus, our measurements are consistent with i) a flattening of the 
light curve due to an underlying host or ii) with a transitory plateau
phase spanning at least 8.3 days (from Oct 1.9 to Oct 10.2 UT).

The elongated appearance of the object supports the first hypothesis (i).
A combination of both effects could be also possible.

Further observations are planned.

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