GCN Circular no. 2515


GRB040106, likely optical afterglow

Nicola Masetti, Eliana Palazzi (IASF/CNR, Bologna), Evert Rol, Elena
Pian (INAF, OA Trieste) and Emanuela Pompei (ESO) on behalf of GRACE,
report:


We have observed the Integral error circle of GRB 040106 (Mereghetti
et al., GCN 2505), on two consecutive nights (6-7 and 7-8 Jan 2004) at
the ESO NTT with EMMI in R band.

Within the error circle of the XMM-Newton counterpart (Ehle et al.,
GCN 2508), we find only one source which shows a clear fading
behaviour, as follows:

  mid obsdate, UT       filter  exptime    magnitude   err(magn)

  07/01/04, 08:33       R       10 min      22.4         0.1
  08/01/04, 08:25       R       20 min      23.7 (*)     0.3

* 2 sigma detection

The magnitudes are calibrated using the USNO-A2.0 star U0375_14656270,
located at coordinates RA = 11:52:18.18, Dec = -46:46:54.3 (J2000),
assuming it has magnitude R = 17.1. The magnitude errors are
statistical only, i.e. they do not include any zero point errors.

All other sources within the XMM-Newton error circle show no sign of
fading, confirming the findings by Fox et al. (GCN 2514). We therefore
identify the fading source as the likely optical afterglow of GRB
040106.

The position of the afterglow is 

  RA  =  11 52 12.27    (J2000)
  Dec = -46 47 15.8     (J2000)

with a 0.5 arcsecond error in both coordinates.

The NTT images can be viewed at
http://www.bo.iasf.cnr.it/~masetti/grb040106.html (source 5 in the
images is the afterglow).

Further observations at all wavelengths are encouraged.

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