[vsnet-grb-info 3305] GRB 060512: TAROT optical observation

[GCN Circulars]

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  5140
SUBJECT: GRB 060512: TAROT optical observation
DATE:    06/05/15 15:07:31 GMT
FROM:    Alain Klotz at CESR-CNRS  <Alain.Klotz at free.fr>

 Klotz, A. (CESR-OMP), Boer M. (OHP), Atteia J.L. (LATT-OMP) report:

We imaged the field of GRB 060512 detected by SWIFT
(trigger 209755) with the TAROT robotic telescope (D=25cm)
located at the Calern observatory, France.

First image was acquired 796.8s after the GRB trigger
(5s after the notice). The field elevation decreased from
65 degrees above horizon and weather conditions
were good but the full moon was at 68 deg from the
GRB position.

We detected the OT source mentioned by Cummings et al
(GCNC 5117). We co-added series of unfiltered
exposures to increase signal to noise ratio:

t-t_trig (min)
begin -   end   CRmag     1*sigma(mag.)
  13.3   34.7   17.64     0.28
  34.8  228.3   19.03     0.60
t_trig = 2006-05-12T23:13:20.640 (Date of trigger)

CR means Clear filter calibrated by R magnitude.
Magnitudes were estimated by PSF fit with the
two following nearby USNO-B1 stars:

1311-0234453 R=16.63 (I=14.94)
1311-0234485 R=17.09 (I=15.87)

We combined R optical observations
(Mundell et al. GCNC 5119,
Malesani et al. GCNC 5122 assuming R=18.65 at t-t_trig=1.2h,
Cenko et al. GCNC 5125,
Milne et al. GCNC 5127)
with those of TAROT.
All these data are compatible with a
decay index alpha 0.85 +/- 0.08 (assuming a
flux decay F(t) = K*t^-alpha).
Complementary data are available on:
http://www.cesr.fr/~klotz/grb060512/

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