TITLE:   GCN CIRCULAR
NUMBER:  19356
SUBJECT: GRB 160425A: Skynet PROMPT-CTIO observations of the optical afterglow
DATE:    16/04/27 18:54:26 GMT
FROM:    Adam S. Trotter at UNC-Chapel Hill/PROMPT/Skynet  <atrotter@physics.unc.edu>

A. Trotter, D. Reichart, J. Haislip, J. Moore, N. Frank, M. Maples, E. Johnson, R. Joyner, J. Martin, C. Salemi, J. A. Crain, K. Ivarsen, A. LaCluyze, and M. Nysewander report:

Skynet observed the Swift BAT/XRT localization of the unusual GRB 160425A (Krimm et al., GCN 19343, Swift trigger=684098) with with two 16" telescopes (P5, P6), and twp 24" telescopes (P1, P8) of the PROMPT array at CTIO, Chile. Starting at 2016-04-25 01:34 UT and continuing until 10:14 UT (t=2.1-10.8h post-trigger), Skynet took a total of 849 160s exposures in the I band (P1, P5), V band (P6) and B band (P8).  

We detect a fading optical afterglow in I-band images at the UVOT position reported by Krimm et al. (GCN 19343), with I~17 at t=2.2h and I~20 at t=7.3h. 

A preliminary light curve is at:
http://www.skynet.unc.edu/grb/grb160425a.png

Preliminary magnitudes are in the Vega System, calibrated to 8 APASS DR9 stars in the field.  Magnitudes have not been corrected for line-of-sight Milky Way dust extinction, with expected E(B-V)=0.05 (Schlafly & Finkbeiner 2011).

No further Skynet observations are scheduled.