GCN Circular 21727

Klotz A., Turpin D., Atteia J.L. (CNRS-OMP-IRAP),
Boer, M., Laugier, R. (CNRS-ARTEMIS),
Gendre B. (UVI - Etelman Obs.) report:

We imaged the field of GRB 170823A detected by SWIFT
(trigger 769177) with the TAROT robotic telescope (D=25cm)
located at the Calern observatory, France.

The observations started 28s after the GRB trigger
(18s after the notice). The elevation of the field decreased from
3 degrees above horizon and weather conditions
were very 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 do not detect any OT with a limiting magnitude of:
t0+28s to t0+88s : Rlim = 15.1

The second image is 30.0s exposure in tracking mode:
t0+101s to t0+131s : Rlim = 15.1

We co-added a series of exposures:
t0+101s to t0+395s : Rlim = 16.8

Magnitudes were estimated with the nearby USNO-B1 stars
and are not corrected for galactic dust extinction.