GCN Circular 21052

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 170428A detected by SWIFT
(trigger 750298) with the TAROT robotic telescope (D=25cm)
located at the European Southern Observatory,
La Silla observatory, Chile.

The observations started 25s after the GRB trigger
(15s after the notice). The elevation of the field increased from
18 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 GROND position provided
by Bolmer et al. (GCNC 21050) with a limiting magnitude of:
t0+25s to t0+85s : Rlim = 17.5

The second image is 30.0s exposure in tracking mode:
t0+98s to t0+128s : Rlim = 18.2

We co-added a series of exposures:
t0+98s to t0+388s : Rlim = 19.2

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