TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  689
SUBJECT: GRB 000418: Detection of the Host Galaxy
DATE:    00/06/07 01:09:22 GMT
FROM:    Josh Bloom at CIT  <jsb@astro.caltech.edu>

GRB 000418: Detection of the Host Galaxy

J. S. Bloom, A. Diercks, T. J. Galama, A. Mahabal, S. R. Kulkarni, F. A.
Harrison, P. Mao (Caltech) and D. Helfand (Columbia), on behalf of the
larger Caltech-NRAO-CARA GRB collaboration, report:

``We have detected two components of the putative host galaxy of GRB
000418 (Hurley et al. GCN #642; Klose et al. GCN #645): an optically
bright component at the position of the transient and an extended red
component.

Our optical observations were conducted on 2 May 2000 UT with the
Echellete Spectrograph Imager (ESI) on Keck II and on 29 May 2000 UT with
COSMIC on the Palomar 200-inch Telescope.  The light curve at the position
of the optical transient has appeared to level off in R-band.  Fitting the
light curve with a power-law + constant flux, we find this component (at
the position of the OT) has R = 24.0 +/- 0.3 mag (1-sigma) and the decay
constant is alpha=-1.3 +/- 0.3 (1-sigma). This is consistent with the
detection of strong emission lines at the position of the OT (Bloom et al.
GCN #661).

In the infrared, we obtained 92 minutes of Ks-band imaging on 13 May 2000
of the field of GRB 000418 with NIRC on the Keck I 10-m Telescope.  In
~0.5 arcsec seeing (FWHM), we detect both the IR transient and a faint
galaxy extended (3--4 arcsec) to the southeast from the transient.  The
transient appears to lie on the edge of the extended K-band emission.

Together, the imaging and spectroscopic data suggest a possible
association of the GRB with a bright star-forming region in an otherwise
red galaxy."

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