We present the spectroscopic discovery of a broad-lined Type Ic supernova ( SN 2010bh ) associated with the nearby long-duration gamma-ray burst ( GRB ) 100316D .
At z = 0.0593 , this is the third-nearest GRB-SN .
Nightly optical spectra obtained with the Magellan telescopes during the first week after explosion reveal the gradual emergence of very broad spectral features superposed on a blue continuum .
The supernova features are typical of broad-lined SNe Ic and are generally consistent with previous supernovae associated with low-redshift GRBs .
However , the inferred velocities of SN 2010bh at 21 days after explosion are a factor of \sim 2 times larger than those of the prototypical SN 1998bw at similar epochs , with v \approx 26,000 km s ^ { -1 } , indicating a larger explosion energy or a different ejecta structure .
A near-infrared spectrum taken 13.8 days after explosion shows no strong evidence for He i at 1.083 µm , implying that the progenitor was largely stripped of its helium envelope .
The host galaxy is of low luminosity ( M _ { R } \approx - 18.5 mag ) and low metallicity ( Z \lesssim 0.4 Z _ { \odot } ) , similar to the hosts of other low-redshift GRB-SNe .