[vsnet-grb-info 8605] GRB 090926a, SMARTS optical/IR afterglow observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  10113
SUBJECT: GRB 090926a, SMARTS optical/IR afterglow observations
DATE:    09/10/30 07:27:25 GMT
FROM:    Bethany Cobb at UC Berkeley  <bcobb at astro.berkeley.edu>

B. E. Cobb (UC Berkeley) reports:

Using the ANDICAM instrument on the 1.3m telescope at CTIO, we
obtained optical/IR imaging of the error region of GRB 090926a
(GCN 9933, Bissaldi et al.) over several epochs.  For each epoch,
total summed exposure times amounted to 36 minutes in I and
30 minutes in J.

The afterglow of GRB 090926a (e.g. GCN 9937, Haislip et al.;
GCN 9938, Gronwall et al.) is detected in our images with
the following magnitudes (calibrated using Landolt standard stars
in the optical and 2MASS stars in the IR):

time
post-burst      I mag           J mag
20.60 hrs       18.17+/-0.06    17.28+/-0.07
71.74 hrs       19.53+/-0.07    18.35+/-0.09
119.18 hrs      20.33+/-0.10    19.16+/-0.13

Between ~21 and 119 hours post-burst, the afterglow fades
with a rate of alpha ~ -1.1+/-0.1 (where afterglow flux is
proportional to t^alpha).