[vsnet-grb-info 13326] GRB 130427A: Skynet detections of a possible supernova

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  14662
SUBJECT: GRB 130427A: Skynet detections of a possible supernova
DATE:    13/05/15 17:02:50 GMT
FROM:    Adam S. Trotter at UNC-Chapel Hill/PROMPT/Skynet  <atrotter at physics.unc.edu>

A. Trotter, D. Reichart, J. Haislip, A. LaCluyze, K. McLin, L. Cominsky, 
A. Smith, D. Caton, L. Hawkins, B. Holmes, T. Linder, 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 has 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); the 14" 
GLAST Optical Robotic Telescope (GORT) at the Hume Observatory in 
California (RcIc bands); the 14" Deep Sky Observatory (DSO-14) telescope 
at Pisgah National Forest, NC; and the 30" telescope at the Astronomical 
Research Observatory (ARO-30) in Westfield, IL. Our observations now 
span 18 nights, from t=0.65 to 17.6 days post-trigger. Skynet has taken 
3420 160-second exposures on the 4 PROMPT telescopes, 420 160-second 
exposures on GORT, 91 160s exposures on DSO-14 and 133 60-160s exposures 
on ARO-30, or a total of over 178 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 18.

In Trotter et al. (GCN 14608) we reported a flattening of the light 
curve at t~10 days.  That flattening has continued, with possible 
chromatic bumps in V, R and I bands at ~14d, 11d and 10d, respectively.  
Our most recent observations, at t=17.8d, show a rebrightening in V, R 
and I bands; we speculate that this may be the onset of the classical 
supernova, which was detected spectroscopically by de Ugarte Postigo et 
al. (GCN 14646) at t=16.7 days.

A preliminary light curve including all Skynet observations through 
t=17.8 days is at:
http://skynet.unc.edu/grb/grb130427a_17.png

Further observations are scheduled.