Daniele Malesani (DARK/NBI), Andrew J. Levan (Univ. Warwick), Johan P.
U. Fynbo (DARK/NBI), report on behalf of the X-shooter GRB collaboration:
We observed the field of the short GRB 100702A (Siegel et al., GCN
10916) with the ESO VLT equipped with X-shooter.
In the R-band acquisition image, taken starting on 2010 July 2 at 2:05
UT (1 hr after the GRB), we detect two pointlike sources within the XRT
error circle (Siegel et al., GCN 10916):
A: RA = 16:22:47.05, Dec = -56:31:53.3, R = 15.49
B: RA = 16:22:47.27, Dec = -56:31:55.4, R = 17.20
A third object is located just above the XRT circle:
C: RA = 16:22:47.30, Dec = -56:31:50.6, R = 17.25
Photometry was computed against USNO-B1. Sources A and C are clearly
visible in the DSS, while source B can be barely spotted, blended with
source A. A finding chart is visible at the following URL:
A second R-band image was taken 48 minutes after, and none of the above
mentioned sources vary by more than 0.05 mag during this time span. For
an afterglow decay proportional to t^-1, a variation of ~0.6 mag would
It is thus likely that none of the above sources is related to the GRB.
This is not surprising given the moderately crowded field (at Galactic
latitude b = -5 deg). We note that the glare from the above mentioned
bright objects makes it difficult to identify faint sources within the
XRT error circle.
We acknowledge excellent and prompt support from the observing staff at
Paranal, in particular Christophe Martayan, Andrew Fox, Vincenzo
Mainieri, Manuel Olivares, Thomas Szeifert, and the visitor observer,