[vsnet-grb-info 4509] GRB 070412: further NOT observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  6281
SUBJECT: GRB 070412: further NOT observations
DATE:    07/04/12 09:01:56 GMT
FROM:    Daniele Malesani at Niels Bohr Inst,Dark Cosmology Center  <malesani at astro.ku.dk>

Daniele Malesani (DARK/NBI) and Helene Uthas (NOT) report on behalf of a
larger collaboration:

We observed again the field of GRB 070412 (Romano et al., GCN 6273) with
the NOT. Observations were carried out at two epochs, ~0.9 and ~3.5 hr
after the GRB. R- and I-band images were secured at each epoch.

Inside the XRT error circle, we do not detect the sources reported by
Jelinek et al. (GCN 6279) and Berger (GCN 6280). The 3-sigma limiting
magnitudes are:

t-t0     I limit   R limit
--------------------------
0.9 hr   22.9      24.0
3.5 hr   23.1      24.2

These numbers were computed assuming R = 17.38 and I = 17.17 for the USNO
star at RA = 12:06:02.17, Dec = +40:09:01.4. We note that the magnitude
reported by Berger (GCN 6280) is fainter than our limits. Our early
measurement implies a decay shallower than ~t^-0.7.

The object reported by Malesani & Uthas (GCN 6276) is detected only in the
first R-band image, thus leaving open the possibility that this source was
fading. However, we caution about the low significance of this detection.