[vsnet-grb-info 2080] GRB 050904: SOAR YJ and PROMPT Ic Observations

[GCN Circulars]

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  3919
SUBJECT: GRB 050904: SOAR YJ and PROMPT Ic Observations
DATE:    05/09/05 07:04:32 GMT
FROM:    Daniel E. Reichart at U.North Carolina  <reichart at physics.unc.edu>

J. Haislip, M. Nysewander, D. Reichart, E. Cypriano, D. Maturana, S.
Pizarro, C. MacLeod, J. Kirschbrown, E. Figueredo report on behalf of the
UNC team of the FUN GRB Collaboration.

We continued observations of the afterglow (Haislip et al., GCN 3913) of
GRB 050904 (Cummings et al., GCN 3910) with SOAR and PROMPT at CTIO in YJ
and Ic, respectively, beginning 26.4 hours after the burst.

We detect the afterglow in J and refine the fading rate to be -1.00 +/-
0.12.

We also detect the afterglow in Y, which suggests that the redshift is at
the lower end of the redshift ranges of Haislip et al. (GCN 3914) and
Reichart (GCN 3915).

Furthermore, a redshift of 6 (+/- 1) appears to be consistent with the
relatively faint, unfiltered optical detections of Klotz et al. (GCN 3917)
from only minutes after the burst:  Extrapolation of our J-band light curve
back to this time suggests that the afterglow was probably relatively
bright (J ~ 13 mag) redward of the Ly-alpha forest.  Integration of the
light across a broad optical spectral response curve would then result in
significantly fainter magnitudes for such redshifts.