[vsnet-grb-info 8551] GRB 091020: Additional Lick observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  10060
SUBJECT: GRB 091020: Additional Lick observations
DATE:    09/10/22 14:22:00 GMT
FROM:    Daniel Perley at U.C. Berkeley  <dperley at astro.berkeley.edu>

D. A. Perley (UC Berkeley) reports:

Further to observations the previous night (GCN 10058), I re-observed 
the afterglow of GRB 091020 between UT 2009-10-22 12:23 and 13:25 using 
the Nickel 40-inch telescope at Lick Observatory in a series of 
seventeen 180 second exposures (51 minutes total integration) in R-band.

The afterglow is detected in in the combined stack of all frames. 
Calibrating relative to the same SDSS standard stars as in GCN 10058, 
the estimated magnitude of the afterglow at this time is:

R = 21.81 +/- 0.23 mag  (t_mid = 39.29 hr)

The implied average decay index over the 24 hours since the previous 
observation is alpha=0.87.