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GCN Circular 9026

Subject
GRB 090323: GROND Detection of the Afterglow and Photo-z
Date
2009-03-24T05:06:41Z (15 years ago)
From
Adria C. Updike at Clemson U <aupdike@clemson.edu>
Adria C. Updike (Clemson University), Robert Filgas (Tautenburg Obs.),
Thomas Kruehler, Jochen Greiner (MPE Garching), and Sheila McBreen
(University College Dublin) report on behalf of the GROND team:

We observed the field of GRB 090323 (Fermi trigger 259459364 / 090323002;
Ohno et al., GCN #9021) 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 02:50 UT on March 24, 26 hours and 48 minutes time
after the GRB trigger, and are continuing. They were performed at an
average seeing of 1.3" and at an average airmass of 1.8.

We found a single point source within the 2.7" Swift-XRT error circle
reported by Kennea et al. (GCN #9024) at

RA (J2000.0) = 12h 42m 50.29s

DEC (J2000.0) = +17d 03' 11.6"

with an uncertainty of 0.5".

Based on the first 8 min of total exposures in g'r'i'z' J H Ks, we
estimate preliminary magnitudes (all in AB system) of

g' = 21.64 +/- 0.07 mag,

r' = 20.03 +/- 0.03 mag,

i' = 19.64 +/- 0.02 mag,

z' = 19.39 +/- 0.02 mag,

J = 19.24 +/- 0.02 mag,

H = 18.86 +/- 0.02 mag, and

K = 18.58 +/- 0.03 mag

Given magnitudes are calibrated against GROND zeropoints as well
as 2MASS field stars 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).

Based on the given magnitudes, we find a photometric redshift of z = 4.0
+/- 0.3.
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