TITLE:   GCN CIRCULAR
NUMBER:  13766
SUBJECT: GRB 120913B: TAROT La Silla observatory optical photometry
DATE:    12/09/14 01:16:07 GMT
FROM:    Alain Klotz at CESR-CNRS  <Alain.Klotz@free.fr>

Klotz A. (IRAP-CNRS-OMP), Gendre B. (ASDC/INAF-OAR),
Boer M. (UNS-CNRS-OCA), Atteia J.L. (IRAP-CNRS-OMP) report:

We continue to observe the afterglow of GRB 120913B
(LaCluyze et al. GCNC 13764). A rapid photometric
analysis gives the following magnitudes:

t0+Mid(s)  Rmag
    159     16.5
    200     16.3
    281     15.8
    351     15.9
    451     16.2
    652     16.6
   1054     17.0

We measure an optical decay alpha=-1 from
observations after 300s, i.e. after the
optical peak.

Considering the optical decay, optical
predicted magnitudes are:

2012-09-14T00:56 UT R=18.4 (t0+1h)
2012-09-14T01:56 UT R=19.1 (t0+2h)
2012-09-14T02:56 UT R=19.6 (t0+3h)
2012-09-14T03:56 UT R=20.0 (t0+4h)
2012-09-15T00:56 UT R=21.0 (t0+1day)

These predictions can help spectrometry
observations.