A. Trotter, N. Frank, A. LaCluyze, D. Reichart, K. McLin, L. Cominsky,
T. Berger, J. A. Crain, H. T. Cromartie, R. Egger, A. Foster, J.
Haislip, K. Ivarsen, M. Maples, J. Moore, M. Nysewander, and E.
Skynet observed the Swift/BAT localization of GRB 130420A (Page et al.,
GCN 14406, Swift trigger 553977) with the 14" GLAST Optical Robotic
Telescope (GORT) at the Hume observatory in California, beginning ~100s
after the trigger in RcIc, and continuing until the source set at
t=4.9h. We detect the afterglow reported by Guidorzi et al. (GCN 14405)
at RA 13:04:06.6, Dec +59:25:25.2 (J2000), within the error circle
reported by the Swift XRT (GCN 14406). Photometry was calibrated to six
SDSS stars in the field.
The afterglow exhibits a rising light curve in both Rc and Ic bands at
early times, peaking at t=330s (peak Rc~16, Ic~15.5), after which it
fades with an approximate temporal index alpha~-1. There is some
evidence for flattening of the Ic-band light curve at t>1h, at which
Follow-up observations at GORT have been scheduled.
A preliminary light curve of the first night's data can be found at: