GCN Circular 7779
Subject
GRB 080523: afterglow confirmation and redshift constraints
Date
2008-05-29T18:22:30Z (16 years ago)
From
Daniele Malesani at Niels Bohr Inst,Dark Cosmology Center <malesani@astro.ku.dk>
D. Malesani, J. P. U. Fynbo (DARK/NBI), A. de Ugarte Postigo (ESO), P.
Jakobsson (Univ. Hertfordshire), J. Hjorth, B. Milvang-Jensen
(DARK/NBI), report on behalf of a larger collaboration:
We observed again the field of GRB 080523 (Stroh et al., GCN 7767) with
the ESO VLT equipped with the FORS2 camera. Observations were carried
out on 2008 May 28, at mean time 9:35 UT (4.5 days after the GRB) in the
R band.
The optical source identified by Fynbo et al. (GCN 7770) has clearly
faded since our previous observation by at least 1.5 mag. This confirms
that the object is the afterglow of GRB 080523. The refined coordinates
(J2000, against USNO-B1.0) are
RA = 01:23:11.56
Dec = -64:01:51.59
Residual, marginally significant emission is still detected close to the
afterglow position. It is unclear whether this is related to the GRB.
A finding chart showing the field in the two epochs is posted at
http://www.astro.ku.dk/~malesani/GRB/080523/080523_finder.jpg
Close inspection of our spectra (Fynbo et al., GCN 7770) fails to reveal
any convincing absorption or emission feature. The object has a blue
continuum, and flux is detected down to ~4070 AA. A conservative limit
to the redshift is set by the absence of Lyman-alpha forest redward of
~4900 AA, which implies z < 3. This limit rules out a high redshift as
suggested by the burst gamma-ray properties (Palmer et al., GCN 7772).
We acknowledge significant support from the ESO staff at Paranal,
particularly Linda Schmidtobreick.
