A. Trotter, D. Reichart, J. Haislip, A. LaCluyze, K. McLin, L. Cominsky,
T. Berger, H. T. Cromartie, R. Egger, A. Foster, N. Frank, K. Ivarsen,
M. Maples, J. Moore, M. Nysewander, E. Speckhard, and J. A. Crain report:
Skynet continued observing the Swift/XRT localization of GRB 130427A
(Maselli et al., GCN 14448, Swift trigger #554620) with four 16"
telescopes of the PROMPT array at CTIO, Chile (BVRI bands), and with the
14" GLAST Optical Robotic Telescope (GORT) at the Hume Observatory in
California (RcIc bands). Our observations span 10 nights, from t=0.65 to
10.8 days post-trigger. Skynet has taken 2684 160-second exposures on
the 4 PROMPT telescopes, and 360 160-second exposures on GORT, or a
total of over 135 hours on source. We performed photometry on each
exposure, calibrated to two SDSS stars in the field. We stacked
exposures to improve sensitivity, in groups ranging from 3 exposures on
night 1, to 60 exposures on night 10.
We detect a fading afterglow in BVRI at the position reported by Elenin
et al. (GCN 14450), which is ~50" south of the initial XRT localization.
From night 2 onwards, the light curves fade with an approximate power
law index alpha=-1 (with no corrections for the known host galaxy flux).
We see some evidence for flattening of the I-band light curve beginning
at t~8 days, and of the R-band curve at t~10 days, though it is not
clear whether this is due to host galaxy contamination or to an
A preliminary light curve including all Skynet observations through
t=10.8 days is at:
See Trotter et al. (GCN 14497, GCN 14510) for descriptions and light
curves of the first and second nights' observations. Further Skynet
observations are ongoing.