[vsnet-grb-info 14183] GRB 131117A: TAROT La Silla observatory optical observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  15497
SUBJECT: GRB 131117A: TAROT La Silla observatory optical observations
DATE:    13/11/17 16:32:51 GMT
FROM:    Alain Klotz at IRAP-CNRS-OMP  <Alain.Klotz at free.fr>

Klotz A., Turpin D. (IRAP-CNRS-OMP), Gendre B.,
Boer M., Siellez K., Dereli H., Bardho O. (UNS-CNRS-OCA),
Atteia J.L. (IRAP-CNRS-OMP) report:

We imaged the field of GRB 131117 detected by SWIFT
(trigger 577968) with the TAROT robotic telescope (D=25cm)
located at the European Southern Observatory,
La Silla observatory, Chile.

The observations started 40s after the GRB trigger
(14s after the notice). The elevation of the field decreased from
71 degrees above horizon and weather conditions
were good.

The first image is trailed with a duration of 60.0s
(see the description in Klotz et al., 2006, A&A 451, L39).
We detect the OT discovered by Trotter et al. (GCNC 15491)
and confirmed by Tanga et al. (GCNC 15493). The OT is seen
at a constant level considering the 2 sigma error of +/- 0.5
mag.

t0+40s to t0+46s  R=17.0 +/-0.5
t0+46s to t0+52s  R=17.0 +/-0.5
t0+52s to t0+58s  R=17.0 +/-0.5
t0+58s to t0+64s  R=17.0 +/-0.5
t0+64s to t0+70s  R=17.0 +/-0.5
t0+70s to t0+76s  R=17.0 +/-0.5
t0+76s to t0+82s  R=17.0 +/-0.5
t0+82s to t0+88s  R=17.0 +/-0.5
t0+88s to t0+94s  R=17.0 +/-0.5
t0+94s to t0+100s R=17.0 +/-0.5

Then series of image acquired in tracking mode
shows the decay of the OT:

t0+113s to t0+173s   R=17.2  +/-0.1
t0+194s to t0+464s   R=18.8  +/-0.2
t0+630s to t0+1080s  R=19.0  +/-0.2
t0+1472s to t0+2192s R=19.1  +/-0.2
t0+2524s to t0+4324s Rlim=20.0

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