[vsnet-grb-info 5837] GRB 080320: Gemini-N optical afterglow

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  7488
SUBJECT: GRB 080320: Gemini-N optical afterglow
DATE:    08/03/20 17:00:48 GMT
FROM:    Nial Tanvir at IofA U.Cambridge  <nrt at ast.cam.ac.uk>

N. R. Tanvir, E. Rol (U. Leicester), A. Stephens (Gemini), report
on behalf of a larger collaboration:

We obtained griz observations of the field of GRB 080320 starting
approximately 80 mins post-burst with Gemini-N/GMOS.  Conditions were
rather poor, with some cirrus, which reduced the depth of the images.
A 2nd epoch of i-band imaging was obtained 9 hours post-burst.

A fading point source is seen in both i-band images, somewhat outside
the enhanced XRT error circle (GCN 7479).  The position (J2000) of
this counterpart, with respect to nearby SDSS stars, is (to 0.25
arcsec in each coordinate):

 RA =  11 50 56.427
 dec= +57 09 23.90

The SDSS galaxy noted in GCN 7480 is about 3 arcsec away from the
counterpart, and therefore probably unrelated to it.

Preliminary photometry (again relative to SDSS field stars) gives
i'=22.9, and fading between the epochs of 0.37+/-0.03 mag. This
relatively slow rate of fading could indicate a contribution from a
host galaxy.  The counterpart is seen in the z-band, but is absent (or
very faint) in the r-band image with a limit of about r~24.  This red
r-i colour could be explained by a Lyman-alpha break if the redshift
is z~4.5 to 5.

Further analysis is ongoing.