[vsnet-grb-info 7112] GRB 081222: GROND Detection of the Optical/NIR Afterglow

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  8693
SUBJECT: GRB 081222: GROND Detection of the Optical/NIR Afterglow
DATE:    08/12/22 08:42:04 GMT
FROM:    Adria C. Updike at Clemson U  <aupdike at clemson.edu>

A. Updike (Clemson University), P. Afonso, C. Clemens, and J. Greiner (all
MPE Garching) report on behalf of the GROND team:

We observed the field of GRB 081222 (Swift trigger 337914, Grupe et al.,
GCN #8691) simultaneously in g'r'i'z'JHK with GROND (Greiner et al. 2008,
PASP 120, 405) mounted at the 2.2 m ESO/MPI telescope at La Silla
Observatory (Chile).

Observations started at 05:26 UT on Dec 22, 2008, 32 min after the GRB
trigger. They were performed at an average seeing of 1.0" and at high
airmass.

We detect the source within the Swift-XRT error circle reported by
Grupe et al. (GCN #8691) and Covino et al. (GCN #8692) at

RA (J2000.0) = 01h 30m 57.56s
DEC (J2000.0) = -34d 05' 41.5''

with an uncertainty of 0.5".

We obtained 8 min of total exposures in g'r'i'z'JHK.  Preliminary
magnitudes (calibrated against field stars in the USNO B1.0 and 2MASS
catalogs), exposure length (in seconds, NIR bands co-added), and midtimes
are as follows.

BAND     MAGNITUDE        EXP   MIDTIME (UT)
--------------------------------------------
g'      19.08 +/- 0.01    115    05:27:13
i'      18.04 +/- 0.01    115    05:27:13
z'      18.24 +/- 0.01    115    05:27:13
J       16.12 +/- 0.03    480    05:29:18
H       15.45 +/- 0.02    480    05:29:18
K       14.92 +/- 0.03    480    05:29:18


Tracking problems made data reduction difficult, especially in the r'
band, in which we detect the object but could not properly calibrate the
field.  The object is seen in g' band, implying a redshift smaller than
3.5.  No correction has been made for galactic extinction.