[vsnet-grb-info 2945] GRB 060218A: ROTSE-III Possible Optical Flare

[GCN Circulars]

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  4782
SUBJECT: GRB 060218A: ROTSE-III Possible Optical Flare
DATE:    06/02/19 02:51:12 GMT
FROM:    Robert Quimby at U of Texas/ROTSE  <quimby at astro.as.utexas.edu>

R. Quimby (U Texas), B. E. Schaefer (Louisiana State), H. Swan (U
Mich), report on behalf of the ROTSE collaboration:

ROTSE-IIIb, located at the McDonald Observatory, Texas, responded to
Swift trigger 191157 (possible GRB 060218A; Cusumano et al. GCN 4775;
Barbier et al. GCN 4780). The first image was taken at 03:36:07.9 UT,
97.0 s after the burst (5.9 s after the GCN notice time). We detect a
source coincident with the refined UVOT position reported by Marshall
et al. (GCN 4779). Intermittent clouds reduced the overall data
quality, and after 80 minutes the clouds rendered the images
unusable. We set the following magnitude limits and detection
calibrated relative to the USNO-B1.0 R2 magnitudes:

  tstart(s)    tend(s)   exp(s)    mag      emag    limmag
--------------------------------------------------------------
     96.98      130.61     25      ---       --      15.68
    217.71      472.78    180      ---       --      17.60
    482.43      681.24    180      ---       --      18.55
    690.49     1027.40    300     18.09     0.11     19.00
   1036.55     1789.28    660      ---       --      18.44
   1868.39     4780.74   1680      ---       --      16.91

These magnitudes show that the optical source was significantly
brighter for a ~5-minute interval starting ~12-minutes after the
burst than either before or after this interval, as is consistent with
the two UVOT V-band magnitudes reported by Marshall et al. (GCN 4779).