We present the spectroscopic and photometric evolution of the nearby ( z = 0.059 ) spectroscopically confirmed type Ic supernova , SN 2010bh , associated with the soft , long-duration gamma-ray burst ( X-ray flash ) GRB 100316D .
Intensive follow-up observations of SN 2010bh were performed at the ESO Very Large Telescope ( VLT ) using the X-shooter and FORS2 instruments .
Owing to the detailed temporal coverage and the extended wavelength range ( 3000–24800 Ã ) , we obtained an unprecedentedly rich spectral sequence among the hypernovae , making SN 2010bh one of the best studied representatives of this SN class .
We find that SN 2010bh has a more rapid rise to maximum brightness ( 8.0 \pm 1.0 rest-frame days ) and a fainter absolute peak luminosity ( L _ { bol } \approx 3 \times 10 ^ { 42 } erg s ^ { -1 } ) than previously observed SN events associated with GRBs .
Our estimate of the ejected ^ { 56 } Ni mass is 0.12 \pm 0.02 M _ { \odot } .
From the broad spectral features we measure expansion velocities up to 47,000 km s ^ { -1 } , higher than those of SNe 1998bw ( GRB 980425 ) and 2006aj ( GRB 060218 ) .
Helium absorption lines He I \lambda 5876 and He I 1.083 \mu m , blueshifted by \sim 20,000–30,000 km s ^ { -1 } and \sim 28,000–38,000 km s ^ { -1 } , respectively , may be present in the optical spectra .
However , the lack of coverage of the He I 2.058 \mu m line prevents us from confirming such identifications .
The nebular spectrum , taken at \sim 186 days after the explosion , shows a broad but faint [ O I ] emission at 6340Ã .
The light-curve shape and photospheric expansion velocities of SN 2010bh suggest that we witnessed a highly energetic explosion with a small ejected mass ( E _ { k } \approx 10 ^ { 52 } erg and M _ { ej } \approx 3 Â M _ { \odot } ) .
The observed properties of SN 2010bh further extend the heterogeneity of the class of GRB supernovae .