[vsnet-grb-info 15939] GRB 141221A: TAROT La Silla observatory optical observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  17227
SUBJECT: GRB 141221A: TAROT La Silla observatory optical observations
DATE:    14/12/24 14:38:04 GMT
FROM:    Alain Klotz at IRAP-CNRS-OMP  <Alain.Klotz at free.fr>

Klotz A., Turpin D. (IRAP-CNRS-OMP),
Boer M., Gendre B., Siellez K., Dereli H., Bardho O. (UNS-CNRS-OCA),
Atteia J.L. (IRAP-CNRS-OMP) report:

We imaged the field of GRB 141221A detected by SWIFT
(trigger 622006) with the TAROT robotic telescope (D=25cm)
located at the European Southern Observatory,
La Silla observatory, Chile.

The observations started 31.2s after the GRB trigger
(14.2s after the notice). The elevation of the field increased from
23 degrees above horizon and weather conditions
were good but the dawn interrupted the observations
after 41 minutes.

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 the optical counterpart between 31s
and 68s at a limiting magnitude Rlim = 16.6. Then
the end of the trail shows a sudden appearance of the
optical counterpart (cf. Sonbas et al. GCNC 17206).
Measures are:

  start    end  magnitude
  (sec)  (sec)
   31.2   68.5  Rlim = 16.6
   68.5   74.5  R = 16.0 +/- 0.2
   74.5   80.5  R = 15.7 +/- 0.2
   80.5   86.5  R = 15.5 +/- 0.2
   86.5   92.5  R = 15.6 +/- 0.3

Next images (in tracking mode) show the optical transcient:

  start    end  magnitude
  (sec)  (sec)  R    +/-
  104.6  134.6 15.47 0.03
  145.1  175.1 15.36 0.03
  185.7  215.7 15.40 0.03
  226.0  256.0 15.42 0.03
  266.3  296.3 15.39 0.03
  306.7  396.7 15.60 0.09
  401.3  491.3 16.17 0.02
  715.6  805.6 16.63 0.02
  816.2  906.2 16.68 0.08
1029.4 1119.4 16.95 0.08
1130   1525   17.22 0.08
1536   2486   17.82 0.08

The early afterglow observed by TAROT is compatible
with that observed by PROMPT (Trotter et al. GCNC
17210 and GCNC 17221).

Magnitudes were estimated with the nearby star
NOMAD-1 0982-0272573 R=12.23 and are not corrected
for galactic dust extinction.