[vsnet-grb-info 12261] GRB 120815A: TAROT La Silla observatory optical observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  13646
SUBJECT: GRB 120815A: TAROT La Silla observatory optical observations
DATE:    12/08/15 03:28:29 GMT
FROM:    Alain Klotz at CESR-CNRS  <Alain.Klotz at free.fr>

Klotz A. (IRAP-CNRS-OMP), Gendre B. (ASDC/INAF-OAR),
Boer M. (UNS-CNRS-OCA), Atteia J.L. (IRAP-CNRS-OMP) report:

We imaged the field of GRB 120815A detected by SWIFT
(trigger 531003) with the TAROT robotic telescope (D=25cm)
located at the European Southern Observatory,
La Silla observatory, Chile.

The observations started 34.7s after the GRB trigger
(15.4s after the notice). The elevation of the field decreased from
65 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+34.7s to t0+94.7s : R > 16.3

The second image is 30.0s exposure in tracking mode:
t0+108.0s to t0+138.0s : R > 18.4

We co-added a series of exposures from t0+108s to t0+1605s.
Due to the annouced slew delay announced by Pagani et
al. (GCNC 13645), we analyze the BAT error box.
We compared the co-added TAROT images with the
NOMAD1 catalog sources. Three non catalogued sources
could be an optical counterpart candidate:

ID ra(J2000)    dec(J2000)  Rmag
T1 18:15:57.33 -52:07:35.6  18.5
T2 18:15:58.58 -52:07:27.5  19.0
T3 18:15:35.22 -52:05:21.4  18.3

These sources does not appear in the R filtered DSS image.
The sources does not show any significant brightness
variation durong 20 min. but they are close to the
limiting magnitude in the individual images.
Few other fainter sources are also present in the
TAROT image.

More informations can be found at the following URL:

http://cador.obs-hp.fr/grb120815a

Magnitudes are not corrected for galactic dust extinction.

N.B. Galactic coordinates are lon=342.0422 lat=-15.9869
and the galactic extinction in R band is about 0.3 magnitudes
estimated from D. Schlegel et al. 1998ApJ...500..525S.

This message may be cited.