[vsnet-grb-info 19330] Swift Trigger 748858: TAROT La Silla observatory optical observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  21027
SUBJECT: Swift Trigger 748858: TAROT La Silla observatory optical observations
DATE:    17/04/21 00:57:47 GMT
FROM:    Alain Klotz at IRAP-CNRS-OMP  <Alain.Klotz at free.fr>

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 the trigger 748858 detected by SWIFT
with the TAROT robotic telescope (D=25cm)
located at the European Southern Observatory,
La Silla observatory, Chile.

The observations started 91.6s after the GRB trigger
(14.7s after the notice). The elevation of the field decreased from
22 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 in the BAT error box from
Siegel et al. (GCN 21011) and by Sakamoto et al. (GCN 21017)
with a limiting magnitude of:
t0+92s to t0+152s : Rlim = 18.0

The second image is 30.0s exposure in tracking mode:
t0+165s to t0+195s : Rlim = 18.2

We co-added a series of exposures:
t0+165s to t0+455s : Rlim = 19.2
t0+465s to t0+1356s : Rlim = 19.3

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