TITLE:   GCN CIRCULAR
NUMBER:  9328
SUBJECT: GRB 090509: GROND further analysis and redshift limit
DATE:    09/05/09 12:31:34 GMT
FROM:    Thomas Kruehler at MPE/MPI  <kruehler@mpe.mpg.de>

F. Olivares, T. Kruehler (MPE Garching), S. Klose (Tautenburg), and J. 
Greiner (MPE Garching) report on behalf of the GROND team:

In addition to our previous GCN (Olivares et al., GCN #9326) we report here 
the observed preliminary magnitudes (in the AB system) for the afterglow 
(GCN #9326 and Covino et al., GCN #9327) of GRB 090509 (Grupe et al., GCN 
#9325). Based on 8 min of effective exposure starting at 5:22 UT (12 
minutes after the trigger), we measure

g = 18.12 +/- 0.01
r = 17.75 +/- 0.01
i = 17.48 +/- 0.01
z = 17.22 +/- 0.01
J = 16.87 +/- 0.07
H = 16.57 +/- 0.12
K = 16.31 +/- 0.17

The quoted error is statistical only. There is an additional systematic 
error from the calibration against the GROND zeropoints and 2MASS field 
stars which is expected to be in the 0.1 mag range.

After correcting for a Galactic foreground extinction corresponding to a 
reddening of E_(B-V)=0.206 mag (Schlegel et al.), the g' to K band is well 
described with a single power law. This implies, that Lyman alpha is below 
or very close to the blue edge of the g' band, and constrains the redshift 
to smaller than z < 3.0 (90% confidence limit).