[vsnet-grb-info 3878] GRB 061007 - FTS early brightening and power law decay

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  5709
SUBJECT: GRB 061007 - FTS early brightening and power law decay
DATE:    06/10/07 14:45:18 GMT
FROM:    David Bersier at Liverpool John Moores U  <dfb at astro.livjm.ac.uk>

D. Bersier , C.G. Mundell (Liverpool JMU), C. Guidorzi (Univ Bicocca &
INAF-OAB), A. Gomboc (U. Ljubljana), A. Melandri, C.J. Mottram,
I.A. Steele, R.J. Smith, A. Monfardini, D. Carter, S. Kobayashi,
(Liverpool JMU), E. Rol, P. O'Brien, N. Bannister (Leicester) report:

We observed the optical counterpart of GRB 061007 (GCN 5706, 5707, 5708)
with the 2m Faulkes Telescope South (Siding Spring).  At 142 sec after
trigger time, we measure a magnitude of mR=10.15 +/- 0.04 (calibration based
on USNOB1 R2 mag, which may introduce a 0.3 mag systematic uncertainty).
When compared to the magnitude measured by ROTSE (m=13.6, GCN 5706),
this implies a subtantial brightening in the first 2.5 minutes (more
than a factor of 10 between 26 and 142 seconds).

>From 142s on, the OT is seen to decay. For the next three hours,
the decay followed a power law with an index of about -1.55 +/- 0.05.

The position of the afterglow is 03:05:19.56, -50:30:2.7 +/- 1.2"

Observations and analysis are continuing.