[AAVSO-HEN] GRB080825: Afterglow confirmation and redshift estimate

[grb at aavso.org]

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TITLE:   GCN CIRCULAR
NUMBER:  8137
SUBJECT: GRB080825: Afterglow confirmation and redshift estimate
DATE:    08/08/26 02:43:47 GMT
FROM:    Christina Thoene at Niels Bohr Institute,DARK Cosmo Ctr  <cthoene at astro.ku.dk>

Antonio de Ugarte Postigo (ESO), Christina C. Thoene (DARK/NBI) and Davide
Ricci (Univ. of Liege) report:

We obtained further observations of the candidate optical counterpart
of GRB 080825B (Evangelista et al., GCN 8133) in Bessel-UBVRI bands. The
object is found to be fading in a series of I band images. From 23:18 UT
to 01:41 UT, the candidate afterglow faded from 17.4+/-0.2 to 18.1+/-0.2
mag compared to several USNO-B stars, confirming the reality of the
afterglow proposed by Thoene et al. (GCN 8135). Furthermore the object is
detected in V, R and I band, but not in U and B. We therefore derive a
redshift limit of z>3 if the nondetection is due to Lyman alpha absorption
or z>4.3 if due to the Lyman limit.

Further analysis is ongoing.