TITLE:   GCN CIRCULAR
NUMBER:  11025
SUBJECT: GRB 100728B: Lick Observations
DATE:    10/07/29 05:59:34 GMT
FROM:    Daniel Perley at U.C. Berkeley  <dperley@astro.berkeley.edu>

D. A. Perley, C. R. Klein, and A. N. Morgan (UC Berkeley) report:

We began observations of the afterglow of GRB 100728B (Morris et al., 
GCN 11009; Perley et al., GCN 11007) with the Nickel 40-inch telescope 
at Lick Observatory starting at 10:38:32 UT, 397 sec after the Swift 
trigger.  A series of frames in R-band (as well as one V-band and one 
U-band exposure) was acquired.  The resulting light curve shows a 
gradual, unbroken power-law decay with a decay index consistent with 
that seen in the KAIT observations (Perley et al., GCN 11024). 
Photometry from our first seven R-band exposures is as follows:

tstart(s) exp(s) filt  mag    unc
397        60    R = 17.38 +/- 0.06
830       300    R = 18.33 +/- 0.05
1162      300    R = 18.53 +/- 0.06
1497      200    R = 18.71 +/- 0.07
1888      160    R = 18.88 +/- 0.09
2062      120    R = 18.80 +/- 0.09
2197      120    R = 18.99 +/- 0.11

Calibration is relative to a single bright star at RA=44.041108, 
dec=+0.242409 (SDSS DR6 magnitudes g=15.61, r=14.52, i=14.57; the 
equivalent Cousins R magnitude is R=14.3 using the average of the two 
SDSS Lupton transformations.)  As this star may be weakly blended with a 
faint neighbor and its USNO magnitude (R2=13.94) differs from this SDSS 
value, caution is advised in interpreting the absolute calibration.