[vsnet-grb-info 16214] GRB 150222A: GROND optical afterglow candidate

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  17495
SUBJECT: GRB 150222A: GROND optical afterglow candidate
DATE:    15/02/23 07:15:01 GMT
FROM:    Ana Nicuesa at TLS Tautenburg  <ana at tls-tautenburg.de>

A. Nicuesa Guelbenzu (TLS Tautenburg), P. Wiseman (MPE Garching), and J.
Greiner (MPE Garching) report:

We observed the field of GRB 150222A (Swift trigger 632180; Bernardini et
al., GCN 17486) simultaneously in g'r'i'z'JHK with GROND (Greiner et al.
2008, PASP 120, 405) mounted at the 2.2m MPG telescope at ESO La Silla
Observatory (Chile).

Observations started at 03:39:15 UT on February 23, about 10 hours after
the GRB trigger. Inside the enhanced X-ray error circle (Beardmore et al.,
GCN 17494) we detect a faint source at coordinates RA, DEC (J2000) =
13:15:08.75, -12:09:06.2 with an error of 0".5.

At a mean time of February 23, at 04:39:07 UT, we measure the following
preliminary AB magnitude:


g' = 24.8 +/- 0.2.
r' = 24.6 +/- 0.3.

At present we cannot decide if this is the afterglow. Observations are
ongoing.

Magnitudes are calibrated against GROND zeropoints (g'r'i'z')
and are not corrected for the Galactic extinction
in the direction of the burst.