  We report on the spectroscopic detection of supernova SN 2010ma associated
with the long gamma-ray burst GRB 101219B. We observed the optical counterpart
of the GRB on three nights with the X-shooter spectrograph at the VLT. From
weak absorption lines, we measure a redshift of z = 0.55. The first epoch
UV--near-infrared afterglow spectrum, taken 11.6 hr after the burst, is well
fit by a power law consistent with the slope of the X-ray spectrum. The second
and third epoch spectra (obtained 16.4 and 36.7 days after the burst), however,
display clear bumps closely resembling those of the broad-lined type-Ic SN
1998bw if placed at z=0.55. Apart from demonstrating that spectroscopic SN
signatures can be observed for GRBs at these large distances, our discovery
makes a step forward in establishing a general connection between GRBs and SNe.
In fact, unlike most previous unambiguous GRB-associated SNe, GRB 101219B has a
large gamma-ray energy (E_iso = 4.2 x 10^{51} erg), a bright afterglow, and
obeys the "Amati" relation, thus being fully consistent with the cosmological
population of GRBs.
