Zusammenfassung
We present observations by the Fermi Gamma-Ray Space Telescope Gamma-Ray
Burst Monitor (GBM) of the nearby (z=0.55) GRB 101219B. This burst is a long
GRB, with an associated supernova and with a blackbody component detected in
the early afterglow observed by the Swift X-ray Telescope (XRT). Here we show
that the prompt gamma-ray emission has a blackbody spectrum, making this the
second such burst observed by Fermi GBM. The properties of the blackbody,
together with the redshift and our estimate of the radiative efficiency, makes
it possible to calculate the absolute values of the properties of the outflow.
We obtain an initial Lorentz factor Gamma=1388, a photospheric radius
r\_phot=4.41.9 10^11 cm and a launch radius r\_0=2.71.6 \times
10^7 cm. The latter value is close to the event horizon for a stellar-mass
black hole and suggests that the jet has a relatively unobstructed path through
the star. There is no smooth connection between the blackbody components seen
by GBM and XRT, ruling out the scenario that the late emission is due to
high-latitude effects. In the interpretation that the XRT blackbody is prompt
emission due to late central engine activity, the jet either has to be very
wide or have a clumpy structure where the emission originates from a small
patch. Other explanations for this component, such as emission from a cocoon
surrounding the jet, are also possible.
Nutzer