GCN Circular 13438
Subject
GRB 120711A: GROND photometric redshift
Event
Date
2012-07-11T11:11:49Z (14 years ago)
From
Sylvio Klose at TLS Tautenburg <klose@tls-tautenburg.de>
J. Elliott (MPE Garching), S. Klose (TLS Tautenburg), and J. Greiner (MPE
Garching) report on behalf of the GROND team:
We observed the field of GRB 120711A (INTEGRAL trigger 6599: Gotz et al.,
GCN 13434; Bozzo et al., GCN 13435; MAXI/GSC detection: Serino et al., GCN
13436; Fermi/GBM trigger 363667496 / 120711115: Gruber & Pelassa, GCN
13427) simultaneously in g'r'i'z'JHK with GROND (Greiner et al. 2008, PASP
120, 405) mounted at the 2.2m MPG/ESO telescope at La Silla Observatory
(Chile).
Observations started on July 11, 08:34 UT, 5.8 hrs after the trigger as
soon the location became visible at La Silla. The afterglow (Lacluyze et
al., GCN 13430, 13433; Zheng, GCN 13432) is clearly detected in all bands.
For an exposure of 8 min in JHK and 7.66 min in g'r'i'z', at an average
airmass of 2.5 and an average seeing of 2".0, we measure the following
preliminary AB magnitudes
g' = 20.9 +/- 0.1
r' = 20.2 +/- 0.1
i' = 19.6 +/- 0.1
z' = 19.4 +/- 0.1
J = 18.6 +/- 0.1
H = 18.2 +/- 0.1
K = 18.0 +/- 0.1
The SED, after correction for Galactic reddening along the line of sight
(E(B-V)=0.09 mag; Schlegel et al. 1998), can be described by a power law
(beta ~ 1.4) with a reduced flux in the g-band, suggesting a photometric
redshift of about 3. We note that also the PROMPT afterglow light curve
(http://skynet.unc.edu/grb/grb120711a.png) supports a drop-out in the blue
bands.
Magnitudes are derived based on GROND zeropoints (g'r'i'z') and 2MASS
stars (JHK).