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GCN Circular 2212

GRB 030329: High-Resolution Spectroscopy of the Host
2003-05-07T08:27:34Z (21 years ago)
Josh Bloom at Harvard/CFA <>
GRB 030329: High-Resolution Spectroscopy of the Host

J. S. Bloom (CfA/Harvard), N. Morrell (Las Campanas Observatory),
S. Mohanty (CfA) report:

"Beginning May 7.01 UT, we observed the position of the optical
transient (Peterson & Price, GCN 1985) of GRB 030329 (Vanderspek et
al., GCN #1997) using the Magellan Inamori Kyocera Echelle (MIKE)
Camera on the Baade 6.5 m at the Las Campanas Observatory.  The
dispersion at 7600 Angstrom (Ang) is 0.053 Ang/pixel. The narrow
emission lines (Martini et al., GCN #2013; Della Ceca et al., GCN
#2015; Greiner et al. #2020; Caldwell et al., GCN #2053; Eracleous et
al., GCN #2117), presumably from the host galaxy, are well detected in
each 1800 sec exposure.  Using a fit to the H-alpha line, we find the
heliocentric systemic redshift of the host galaxy is:

         z = 0.168541 +/- 0.000004

(statistical error). This is most precise emission line redshift of a
GRB host galaxy reported to date. This redshift is consistent with the
host redshift reported previously (Greiner et al., GCN #2020;
Eracleous et al., GCN #2117; Caldwell et al., GCN #2053).

The emission lines are resolved in the dispersion direction with a
FWHM (H-alpha) of 1.44 +/- 0.02 Ang (56.1 km/s). While the core of the
emission lines can be fit by a Gaussian, extended wings of emission
and similar velocity substructure within the profiles are apparent. In
particular, we identify a faint emission structure that is ~66 km/s to
the red of the central core. The host plus OT continuum is discernible
in each echelle order redward of ~7000 Ang.

In ~0.4 arcsecond seeing the emission from the host plus OT is still
unresolved in the spatial direction. The compactness, the relatively
low mass implied by the velocity structure of the emission lines, and
the faintness of the host (Blake & Bloom; GCN #2011) all continue to
support the notion of the host of GRB 030329 as an intrinsically
underluminous galaxy (Eracleous et al., GCN #2117). Despite the low
overall star formation rate of the host (Caldwell et al., GCN #2053),
given the high equivalent widths of the detected lines, the
star-formation rate per unit mass may be appreciable."

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