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GCN Circular 9382

2009-05-17T05:00:40Z (15 years ago)
Andrea Rossi at TLS Tautenburg <>
A. Rossi (Tautenburg), P. Afonso and J.Greiner (both MPE Garching)
report on behalf of the GROND team:

We observed the field of GRB 090516 (Swift trigger 352190, B. Rowlinson et
al.,GCN #9374) simultaneously in g'r'i'z'JHK with GROND mounted at the 2.2m
ESO/MPI telescope at La Silla Observatory (Chile). Observations started on
16 May 2009 at 23:04 UT, 14.6 h after the burst.

We detect the afterglow at a position consistent with the enhanced
XRT error circle (A. Beardmore et al., GCN #9376) and NOT (J. Gorosabel et al.,
 GCN #9379) and Faulkes Telescope detections (C. Guidorzi et al., GCN #9375).
With an exposure time of 20min in JHK and 25min in griz, preliminary photometry
 yields the following AB magnitudes:
g =23.60 +-0.1
r =21.44 +-0.1
i =20.38 +-0.1
z =19.95 +-0.1
J =19.6  +-0.1
H =19.2  +-0.1
K =19.1  +-0.2

The quoted error is statistical only. There is an additional systematic
error in the absolute calibration using the GROND zero points and 2MASS
field stars which is expected to be in the 0.2 mag range. Quoted magnitudes
are not corrected for the galactic foreground extinction corresponding to a 
reddening of E_(B-V)=0.05.

Preliminary results fitting the SED with Hyperz give for no reddening a z ~ 4.5
 and for best fitting solution a photometric redshift of 4.1 +- 0.3, with 
 SMC reddening of A_v = 0.4. This SMC photometric redshift is compatible 
 with VLT's spectroscpic redshift of z = 3.9 (A. de Ugarte Postigo et al. 
 GCN #9381).
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