[vsnet-grb-info 20392] GRB 180314A: TAROT La Silla observatory optical observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  22488
SUBJECT: GRB 180314A: TAROT La Silla observatory optical observations
DATE:    18/03/14 17:56:36 GMT
FROM:    Alain Klotz at IRAP-CNRS-OMP  <Alain.Klotz at free.fr>

Klotz A., Noysena K., Atteia J.L. (CNRS-OMP-IRAP),
Boer M., Eymar L. (CNRS-ARTEMIS),
Gendre B. (UVI - Etelman Obs.) report:

We imaged the field of GRB 180314A detected by SWIFT
(trigger 814129) with the TAROT robotic telescope (D=25cm)
located at the European Southern Observatory,
La Silla observatory, Chile.

The observations started 172.7s after the GRB trigger
(83.1s after the notice). The elevation of the field decreased from
77 degrees above horizon and weather conditions were good.

We detected the candidate couterpart mentioned by D'Avanzo et al.
(GCNC 22478), Bolmer (GCNC 22479), Lipunov et al. (GCNC 22481),
Melandri et al. (GCNC 22482) Sbarufatti et al. (GCNC 22484),
Guidorzi et al. (GCNC 22487). TAROT photometry is:

t1(h) t2(h) r(AB) 1sig
0.048 0.056 15.64 0.05
0.059 0.067 16.00 0.05
0.070 0.079 16.34 0.05
0.081 0.090 16.64 0.06
0.093 0.101 16.92 0.07
0.104 0.129 17.26 0.10
0.132 0.182 17.68 0.13
0.227 0.276 18.18 0.19
0.282 0.332 18.32 0.24
0.343 0.443 18.62 0.30

It shows clearly a decay -1.8 until 8 minutes after the trigger
and then a decay -0.92 later. So we suspect a strong reverse shock
during the 8 first minutes.

Magnitudes were estimated with the nearby NOMAD1 stars
and are not corrected for galactic dust extinction.