TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  1560
SUBJECT: XRF 020903: VRI observations
DATE:    02/09/30 19:52:42 GMT
FROM:    Daniele Malesani at Brera Astro. Obs.  <malesani@merate.mi.astro.it>

M. Stefanon, S. Covino, D. Malesani (INAF, Merate Obs., Milan, I), N.
Masetti (IASF/CNR, Bologna, I.), G. Temporin (Inst. fur Astr. Innsbruck,
A), and S. Desidera (Padova Astr. Obs., I), on behalf of a larger
Italian collaboration, communicate:

We observed the variable source in the field of XRF 020903 (Ricker et
al., GCN 1530; Soderberg et al, GCN 1554) on 29.9 UT, with the 182cm
telescope at Cima Ekar-Asiago, near Padova (Italy). The object was at
high airmass.

We find the following magnitudes with respect to the USNO stars (1) and
(2) reported in the finding chart of Soderberg et al. (see
http://www.astro.caltech.edu/~ams/XrF.html ):

Filter  UT      OT - (1)    OT - (2)
--------------------------------------
V       29.923  4.20+-0.09  2.82+-0.09
R       29.931  2.63+-0.01  1.34+-0.01
I       29.937  4.50+-0.13  5.85+-0.13

In the I-band image (300 s exposure), the object is barely visible.
Using the USNO R-magnitudes for the stars 1 (R = 16.0) and 2 (R = 17.1),
we find

R = 18.55 +- 0.2  @29.931 UT (26.5 days after XRF),

where the error is mainly due to calibration. More accurate photometry
will be distributed when available. Our data suggest further brightening
between 28.3 and 29.9 UT, with respect to the value found in Soderberg
et al. web page.

With present data, we cannot say if the varying source is a rising
supernova or a variable radio-loud AGN, as suggested by Gal-Yam (GCN
1556). Further observations are planned this night.

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