TITLE:   GCN CIRCULAR
NUMBER:  10058
SUBJECT: GRB 091020: Lick observations
DATE:    09/10/21 14:24:31 GMT
FROM:    Daniel Perley at U.C. Berkeley  <dperley@astro.berkeley.edu>

D. A. Perley (UC Berkeley) reports:

I observed the location of GRB 091020 (Racusin et al, GCN 10048) 
starting at UT 2009-10-21 12:30 using the Nickel 40-inch telescope at 
Lick Observatory.   A series of nine exposures in R-band were acquired, 
followed by five exposures in I-band and an additional sequence in 
R-band during morning twilight.  All exposures except for the first were 
of 180 seconds duration.

The afterglow is marginally detected in individual frames and 
well-detected in a combined stack.  Calibrating relative to five nearby 
SDSS standard stars transformed to R-band using the transformation 
equation of Lupton (2005), the estimated magnitude of the afterglow in 
the first R-band stack is:

R = 20.91 +/- 0.13 mag  (t_mid = 15.17 hr)

Additional follow-up is planned if weather permits.