TITLE:   GCN CIRCULAR
NUMBER:  6434
SUBJECT: GRB 070521: TAROT La Silla observatory optical observations
DATE:    07/05/21 07:47:14 GMT
FROM:    Alain Klotz at CESR-CNRS  <Alain.Klotz@free.fr>

Klotz, A. (CESR-OMP), Boer M. (OHP), Atteia J.L. (LATT-OMP) report:

We imaged the field of GRB 070521 detected by SWIFT
(trigger 279935) with the TAROT robotic telescope (D=25cm)
located at the European Southern Observatory,
La Silla observatory, Chile.

The observations started 23.8s after the GRB trigger
(8.5s after the notice). The elevation of the field decreased from
from 24 degrees above horizon and weather conditions
were highly variable (cloudy).

The date of trigger : t0 = 2007-05-21T06:51:10.656

The first image is trailed with a duration of 60.0s
from t0+23.8s to t0+83.8s
(see the description in Klotz et al., 2006, A&A 451, L39).
The limiting magnitude is R ~ 17.1.
We do not detect any OT at the XRT position mentioned
by Guidorzi et al. (GCNC 6431) but we have a faint
patch at coordinates 16h10m37.5s (+/-0.5s) +30d14'58"
(+/-5") J2000.0 near the limiting magnitude.

The second image is 30.0s exposure in tracking mode,
no OT is detected:
t0+89.4s to t0+119.4s : R > 17.5

We co-added a series of exposures:
t0+89.4s to t0+570.3s : R > 19.0

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

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