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GCN Circular 9169

Subject
GRB 090419: GROND detection of afterglow candidate
Date
2009-04-20T08:28:04Z (15 years ago)
From
Jochen Greiner at MPI <jcg@mpe.mpg.de>
P. Afonso (MPE Garching), S. Klose (Tautenburg) T. Kruehler and J.Greiner 
(both MPE Garching) report on behalf of the GROND team:

We observed the field of GRB 090419 (Swift trigger 349592, G. Stratta et 
al.,GCN #9161) 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 
19 Apr. 2009 at 23:12 UT, 9.5 h after the burst.

Inside the enhanced XRT error circle (J.P. Osborne et al., GCN #9164) we 
detect a single faint source in the z' and J band at:

RA  (J2000.0) =  13:07:43.13
DEC (J2000.0) = -75:36:22.4

with an uncertainty of 0.5" in each coordinate.

Preliminary photometry yields the following AB magnitudes and upper limits 
in stacked images:

Filter  T_mid[h]  Exp[s]  AB Mag  MagErr
----------------------------------------
g       11.5792   12x369  >24.6
r       11.5792   12x369  >25.1
i       11.5792   12x369  24.9    0.5
z       11.5792   12x369  24.2    0.1
J       11.5859   360x10  23.0    0.2
H       11.5859   360x10  >22.1
K       11.5859   360x10  >21.2


The quoted error is statistical only. There is an additional systematic 
error in the absolute calibration using the GROND zeropoints and 2MASS 
field stars which is expected to be in the 0.2 mag range. Quoted magnitudes 
are not corrected for the significant Galactic foreground extinction 
corresponding to a reddening of E_(B-V)=0.30.

Given the lack of information about variability and the rather high density 
of foreground stars we cannot definitely associate this source with GRB 
090419 at this point. Because of the high Galactic foreground extinction, 
the upper limits in g'r' as well as the i'-z' color are not constraining, and 
the redshift is only constrained to below about 5.
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