GCN Circular 11025
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.