7,460 research outputs found
Neutrino Emissivity of Dense Stars
The neutrino emissivity of compact stars is investigated in this work. We
consider stars consisting of nuclear as well as quark matter for this purpose.
Different models are used to calculate the composition of nuclear and quark
matter and the neutrino emissivity. Depending on the model under consideration,
the neutrino emissivity of nuclear as well as quark matter varies over a wide
range. We find that for nuclear matter, the direct URCA processes are allowed
for most of the relativistic models without and with strange baryons, whereas
for the nonrelativistic models this shows a strong dependence on the type of
nuclear interaction employed. When the direct URCA processes are allowed, the
neutrino emissivity of hadronic matter is larger than that of the quark matter
by several orders of magnitude. We also find that the neutrino emissivity
departs from behavior when the temperature is larger than the difference
in the Fermi momenta of the particles, participating in the neutrino-producing
reactions.Comment: Latex file. 5 figures available on request. accepted in Int. J. Mod.
Phys.
Characterization of Jets in Relativistic Heavy Ion Collisions
Jet quenching is considered to be one of the signatures of the formation of
quark gluon plasma. In order to investigate the jet quenching, it is necessary
to detect jets produced in relativistic heavy ion collisions, determine their
properties and compare those with the jets one obtains in hadron-hadron or
collisions. In this work, we propose that calculation of flow
parameters may be used to detect and characterize jets in relativistic heavy
ion collisions.Comment: 18 pages, 4 figures, more discussions are added, to be published in
Phys. Rev.
On the Limitations of Neutrino Emissivity Formula of Iwamoto
The neutrino emissivity from two and three flavour quark matter is
numerically calculated and compared with Iwamoto's formula. We find that the
calculated emissivity is smaller than Iwamoto's result by orders of magnitude
when is comparable with the temperature. We
attribute it to the severe restriction imposed by momentum conservation on the
phase space integral. We obtain an alternate formula for the neutrino
emissivity which is valid when the quarks and electrons are degenerate and
is large compared to the temperature.Comment: Latex Version 2.09, 15 pages, 5 postscript figures available upon
request, preprint No. IP/BBSR/93-6
One year of monitoring of the Type IIb supernova SN 2011dh
Optical photometry and low resolution spectroscopy of the type IIb
supernova SN 2011dh in M51 are presented, covering the first year after the
explosion. The light curve and spectral evolution are discussed. The early
phase light curve evolution of SN 2011dh is very similar to SN 1993J and SN
2008ax. In the late phase, however, SN 2011dh declines faster than SN 1993J.
The late phase decline in the -band is steeper than in the and
bands, indicating the possibility of dust formation. With a peak -band
absolute magnitude of mag, SN 2011dh is a marginally
faint type IIb event. The reddening corrected colour curves of SN 2011dh are
found to be redder than other well studied type IIb supernovae. The bolometric
light curve indicates 0.09 M of Ni is synthesized during
the explosion. The HeI lines were detected in the spectra during the rise to
maximum. The nebular spectra of SN 2011dh show a box shaped emission in the red
wing of the [OI] 6300-6363 \AA\ feature, that is attributed to H
emission from a shock excited circumstellar material. The analysis of nebular
spectra indicates that M of oxygen was ejected during the
explosion. Further, the [CaII]/[OI] line ratio in the nebular phase is
0.7, indicating a progenitor with a main sequence mass of 10-15 M.Comment: Accepted for publication in MNRA
Optical observations of the fast declining type Ib supernova iPTF13bvn
We present optical UBVRI photometry and medium resolution spectroscopy of the
type Ib supernova iPTF13bvn, spanning a phase of d to d
with respect to -band maximum. The post maximum decline rates indicate a
fast decline with . Correcting for a galactic
extinction and host galaxy extinction of
, the absolute -band magnitude peaks at
M. The bolometric light curve indicates that M of Ni was synthesized in the explosion. The earliest
spectrum (d) shows the presence of He~{\sc i} 5876 \AA\ feature at a
velocity of 15000 km s, which falls rapidly by the time the SN
approaches the epoch of B-band maximum. The photospheric velocity near maximum
light, as indicated by the Fe~{\sc ii} 5169~\AA\ feature, is km
s. The estimate for the Ni mass, together with the estimates for
the ejected mass () and kinetic energy of the explosion
() indicate that iPTF13bvn is a low luminosity type Ib supernova,
with a lower than average ejected mass and kinetic energy. Our results suggest
that the progenitor of iPTF13bvn is inconsistent with a single Wolf-Rayet star.Comment: Accepted for publication in MNRAS, 11 pages, 12 figure
Detection of Minimum-Ionizing Particles and Nuclear Counter Effect with Pure BGO and BSO Crystals with Photodiode Read-out
Long BGO (Bismuth Germanate) and BSO (Bismuth Silicate) crystals coupled with
silicon photodiodes have been used to detect minimum-ionizing particles(MIP).
With a low noise amplifier customized for this purpose, the crystals can detect
MIPs with an excellent signal-to-noise ratio. The NCE(Nuclear Counter Effect}
is also clearly observed and measured. Effect of full and partial wrapping of a
reflector around the crystal on light collection is also studied.Comment: 18 pages, including 5 figures; LaTeX and EP
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