[vsnet-grb-info 19954] GRB 171020A: TAROT Calern observatory optical observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  22041
SUBJECT: GRB 171020A: TAROT Calern observatory optical observations
DATE:    17/10/22 13:08:21 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 171020A detected by SWIFT
(trigger 780845) with the TAROT robotic telescope (D=25cm)
located at the Calern observatory, France.

The observations started 68s after the GRB trigger
(13s after the notice). The elevation of the field
increased from 58 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 do not detect any OT with a limiting magnitude of:
t0+68s to t0+128s : Rlim = 17.5

The OT (Malesani et al., GCN 22029) is detected
in the median of three individual frames:
t0+141s to t0+251s : R = 18.7 +/- 0.35

We co-added a series of exposures. The OT is no
longer detected:
t0+262s to t0+533s : Rlim = 18.9

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