[vsnet-grb-info 12562] GRB 121027A: GROND Confirmation of Rebrightening

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  13926
SUBJECT: GRB 121027A: GROND Confirmation of Rebrightening 
DATE:    12/10/29 19:48:09 GMT
FROM:    Alexander Kann at TLS Tautenburg  <kann at tls-tautenburg.de>

V. Sudilovsky (MPE Garching), D. A. Kann (MPE Garching/Universe Cluster),
T. Krühler (DARK, Copenhagen), and J. Greiner (MPE Garching) report on
behalf of the GROND team:

Following two days of bad weather delay, we observed the field of GRB
121027A (Evans et al., GCN 13906) simultaneously in g'r'i'z'JHK with GROND
(Greiner et al. 2008, PASP, 120, 405) mounted on the 2.2 m MPG/ESO
telescope at La Silla Observatory (Chile).

Observations began at 08:10 on October 29th (mid-time ~2.05 days
post-trigger). They were performed at an average seeing of 1.6" (r'-band)
and at an average airmass of 1.2.

We detect the NIR afterglow reported by Starling et al. (GCN 13911) and
Levan et al. (GCN 13920) in all seven bands.

Based on a 460 sec integration in g'r'i'z' and 1200 sec integration in
JHK, we measure preliminary magnitudes (all in AB system) of

g' = 22.1 +/- 0.2 mag
r' = 21.6 +/- 0.1 mag
i' = 21.3 +/- 0.1 mag
z' = 20.9 +/- 0.1 mag
J  = 20.4 +/- 0.1 mag
H  = 19.7 +/- 0.1 mag
K  = 19.0 +/- 0.1 mag

We note an increase of brightness by ~ 1 magnitude relative to the
observations reported by Levan et al. (GCN 13920) at 32 hours after the
GRB.

Our detection in all bands constrains the redshift of this burst to z < 3.5.

Given magnitudes are calibrated against GROND zeropoints in the optical,
and 2MASS field stars in the NIR, and are not corrected for the expected
Galactic foreground extinction corresponding to a reddening of E(B-V) =
0.02 mag in the direction of the burst (Schlegel et al. 1998).