TITLE:   GCN CIRCULAR
NUMBER:  9778
SUBJECT: GRB 090812: RAPTOR detections during the burst
DATE:    09/08/12 17:15:03 GMT
FROM:    James Wren at LANL  <jwren@nis.lanl.gov>

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

The RAPTOR telescope system responded to Swift trigger
359711 (Stamatikos et al., GCN 9768) under good observing conditions.
Our narrow-field instruments began observing the location at
06:02:32.9 UTC, 24.0 s after the Swift trigger (7.0 s after
receipt of GCN message).  We obtained simultaneous observations
during the gamma-ray emitting interval in Cousins V, R, and I
bands as well as unfiltered data.  We detect the optical
counterpart in all color bands.  Initial analysis of our unfiltered
data calibrated to the USNO-B1 R-band revals the counterpart
brightening until ~T=70s after the trigger and then beginning a
steady decline.  The following table gives selected observations,
not corrected for extinction, from this event.  Further analysis
of the multi-color data is underway.

t-mid(s)    exp(s)     mag     mag-err
--------------------------------------------
26.48        5.0      15.98    0.18
46.08        5.0      15.39    0.11
73.55        5.0      14.84    0.07
91.71        5.0      15.13    0.09
101.21       5.0      15.25    0.10
141.62      10.0      15.63    0.10