Observations of GRB 080905A
Mean time: 2008 Sep 5.867 UT. Smoothed image.
Mean time: 2008 Sep 6.112 UT.
D. Malesani (DARK/NBI), A. de Ugarte Postigo (ESO), J. P. U. Fynbo (DARK/NBI), A. J. Levan (Univ. Warwick), E. Rol (Univ. Leicester), N. R. Tanvir (Univ. Leicester), C. C. Thoene (DARK/NBI), J. Telting (NOT), A. Baran (Cracow Univ.), report on behalf of a larger collaboration:
We observed the field of the short GRB 080905A (Pagani et al., GCN 8180) with the NOT and the VLT telescopes equipped with ALFOSC and FORS2, respectively. The NOT observations started on 2008 Sep 5.854 UT (8.51 hr after the GRB) and the total exposure time was 30 min. The VLT observations started on 2008 Sep 6.097 UT (14.3 hr after the GRB) and the total exposure was 40 min. All images were taken with the R filter.
Inside the XRT error circle, we detect a single, faint source with R ~ 24 (against USNO-B1 stars), visible in both the NOT and VLT images. No variability of the source can be robustly determined, hence we cannot assess the relationship of this object with the GRB, especially given the relatively crowded field (Galactic latitude -12.6). Further observations are planned.
The coordinates of this object are:
RA(J2000) = 19:10:41.73
Dec(J2000) = -18:52:47.3
with an error of ~0.6".
We note that in our NOT images (seeing ~1"), the extended objects identified by Tristram et al. (GCN 8181) appear resolved into several pointlike sources.
Finding charts can be found at the following URL:
http://www.astro.ku.dk/~malesani/GRB/080905A
We acknowledge significant support from the observing staff at Paranal, in particular Swetlana Hubrig, Elena Mason and Andres Pino.
VLT Image of Sep 7.0 UT, different cut levels.
A. de Ugarte Postigo (ESO), D. Malesani (DARK/NBI), A. J. Levan (Univ. Warwick), J. Hjorth (DARK/NBI), N. R. Tanvir (Univ. Leicester), report on behalf of a larger collaboration:
We observed again the field of the short GRB 080905A (Pagani et al., GCN 8180) with the ESO VLT equipped with FORS2. R-band observations were carried out starting on 2008 Sep 7.004 UT (1.50 days after the GRB) and the total exposure time was 40 minutes.
The object located inside the XRT error circle visible in our early VLT images (Malesani et al., GCN 8190) has clearly faded between the two observations, and is thus likely the optical afterglow of GRB 080905A. We note that this object is located outside the revised 2.2"-radius (90%) UVOT-enhanced XRT error circle (distance from center 4.6"), as provided at http://www.swift.ac.uk/xrt_positions/index.php (value of Sep 7.4 UT).
In our second epoch image, which is deeper and has a better seeing (~0.9"), we also note the presence of a bright extended object, possibly a spiral galaxy, about 9" S, 3" E of the afterglow (partially covered by foreground stars).
Finding charts can be found at
http://www.astro.ku.dk/~malesani/GRB/080905A/#epoch2
We acknowledge significant support from the ESO observing staff at Paranal, in particular Elena Mason, Anders Pino and Swetlana Hubrig.
Daniele Malesani, 2008 September 7.