GCN Circular 11008

K. Ivarsen, J. Haislip, D. Reichart, A. LaCluyze, J. Moore, A. Foster, R.
Egger, A. Oza, M. Schubel, A. Trotter, J. A. Crain, and M. Nysewander
report:

Skynet observed the Swift/BAT localization of GRB 100728A (Swift trigger
#430172) with four of the 16" PROMPT telescopes at CTIO beginning 45
seconds after the trigger in BVRI. We detect the afterglow in all filters.

At 50 seconds after the trigger, its magnitude is I = 14.62 +0.08 -0.07
(calibrated to 10 SDSS stars), R = 15.24 +0.07, -0.06 (calibrated to 7
SDSS stars), V = 15.78, +0.08, -0.07 (calibrated to 8 SDSS stars), B =
16.54 +0.21, -0.17 (calibrated to 2 SDSS stars). SDSS transformations were
applied using Jester et al., 2005, ApJ, 130, 873.

PROMPT's BVRI light curve of the first 4.3 minutes after the trigger,
calibrated to SDSS stars, can be found here:
http://skynet.unc.edu/grb/grb100728a.png. Further observations were
limited by morning twilight at PROMPT.