GCN Circular 6410

D. Malesani, C.C. Thoene (DARK), A. Williams (Perth Obs.), J.P.U. Fynbo
(DARK), A.O. Jaunsen (Univ. Oslo) and P.M. Vreeswijk (ESO) report on
behalf of a larger collaboration:

We observed the field of GRB 070509 (Vetere et al., GCN 6394
Not found
 
 
) with the ESO
VLT UT2 equipped with the FORS1 instrument. Short BVRI observations were
carried out between 2007 May 9.144 and 9.155 UT (starting 0.65 hr after
the GRB). We detect three objects close to the XRT position, at the
following coordinates (J2000, 0.5" error):

A:  RA = 15:51:49.29   Dec = -78:39:01.7   R = 23.48 +- 0.24
B:  RA = 15:51:50.37   Dec = -78:39:06.4   R = 23.52 +- 0.25
C:  RA = 15:51:50.91   Dec = -78:39:10.2   R = 22.71 +- 0.16

Objects A and B are inside the XRT error circle as reported by Vetere et
al. (GCN 6400
Not found
 
 
), while objects B and C are inside the XRT error circle as
provided in Nat Butler's web page (revision 1.2,
http://astro.berkeley.edu/~nat/swift/xrt_pos.html). Objects A and C are
extended. Magnitudes are computed at the mean time 9.149 UT (0.78 hr after
the GRB) and are calibrated against the USNO-B1 catalog. The 3-sigma limit
is R = 23.8. A finding chart of the field can be seen here:

http://www.astro.ku.dk/~malesani/GRB/070509/finder_VLT.jpg

Further R-band observations were carried out with the 1.54m Danish
telescope located in La Silla (Chile) and equipped with DFOSC on 2007 May
9.141 (4500 s) and May 13.134 UT (3000 s). Object C is marginally detected
in both images, while objects A and B are below the detection limit.

At this stage, we cannot claim association between the GRB and any of the
above mentioned objects.

We acknowledge excellent support from the observing staff in Paranal, in
particular Alain Smette and Gael James. CT acknowledges Pisco and Bacardi
support from the GROND staff at La Silla.