[vsnet-grb-info 16309] GRB 150314A: Early RAPTOR Detection

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  17590
SUBJECT: GRB 150314A: Early RAPTOR Detection
DATE:    15/03/17 00:43:21 GMT
FROM:    James Wren at LANL  <jwren at lanl.gov>

J. Wren, W.T. Vestrand, P. Wozniak, and H. Davis,
of Los Alamos National Laboratory report:

The RAPTOR network of robotic optical telescopes made observations of Swift
trigger 634795 (Hagen, et al., GCN 17573).  Our narrow-field instruments
located in Los Alamos, NM, USA, arrived on target at 04:55:20.83 UT, T+27.98
seconds after the BAT trigger time.  Our initial 5s exposure shows the
counterpart (Zheng, et al., GCN 17574) at an unfiltered magnitude of
13.11 +- 0.02.  The source fades steadily, reaching magnitude 15.87 +- 0.09
at T+180.38 s, in agreement with the KAIT lightcurve (Zheng, et al., GCN
17585).  We derive a power-law decay slope of -1.50 using 04:54:52.86 as
the BAT T0.  Our unfiltered magnitudes were calibrated to the USNO-B1 R-band
catalog.

The optical counterpart is not detected in any of our persistent wide-field
monitors during the gamma-ray emitting interval.  Typical 3-sigma unfiltered
limiting magnitudes during this period were V~9.8 based on comparison to the
Tycho-2 V-band catalog.