286 research outputs found
A Two-Dimensional Hydrostatically Equilibrium Atmosphere of a Neutron Star with Given Differential Rotation
An analytic solution has been found in the Roche approximation for the
axially symmetric structure of a hydrostatically equilibrium atmosphere of a
neutron star produced by collapse. A hydrodynamic (quasione-dimensional) model
for the collapse of a rotating iron core in a massive star gives rise to a
heterogeneous rotating protoneutron star with an extended atmosphere composed
of matter from the outer part of the iron core with differential rotation
(Imshennik and Nadyozhin, 1992). The equation of state of a completely
degenerate iron gas with an arbitrary degree of relativity is taken for the
atmospheric matter. We construct a family of toroidal model atmospheres with
total masses and total angular momenta , which are acceptable for the
outer part of the collapsed iron core, in accordance with the hydrodynamic
model, as a function of constant parameters of the
specified differential rotation law in spherical
coordinates. The assumed rotation law is also qualitatively consistent with the
hydrodynamic model for the collapse of an iron core.Comment: 9 pages, 6 figures, 1 tabl
A hydrodynamic model for asymmetric explosions of rapidly rotating collapsing supernovae with a toroidal atmosphere
We numerically solved the two-dimensional axisymmetric hydrodynamic problem
of the explosion of a low-mass neutron star in a circular orbit. In the initial
conditions, we assumed a nonuniform density distribution in the space
surrounding the collapsed iron core in the form of a stationary toroidal
atmosphere that was previously predicted analytically and computed numerically.
The configuration of the exploded neutron star itself was modeled by a
torus with a circular cross section whose central line almost coincided with
its circular orbit. Using an equation of state for the stellar matter and the
toroidal atmosphere in which the nuclear statistical equilibrium conditions
were satisfied, we performed a series of numerical calculations that showed the
propagation of a strong divergent shock wave with a total energy of 0.2x10^51
erg at initial explosion energy release of 1.0x10^51 erg. In our calculations,
we rigorously took into account the gravitational interaction, including the
attraction from a higher-mass (1.9M_solar) neutron star located at the
coordinate origin, in accordance with the rotational explosion mechanism for
collapsing supernovae.W e compared in detail our results with previous similar
results of asymmetric supernova explosion simulations and concluded that we
found a lower limit for the total explosion energy.Comment: 13 pages, 5 figures, 2 table
Analytic solution for kinetic equilibrium of beta-processes in nucleonic plasma with relativistic pairs
The analytic solution is obtained describing kinetic equilibrium of the
-processes in the nucleonic plasma with relativistic pairs. The nucleons
are supposed to be non-relativistic and non-degenerate, while the
electrons and positrons are ultra-relativistic due to high temperature
K), or high density g/cm), or both, where
is a number of nucleons per one electron. The consideration is simplified
because of the analytic connection of the density with the electron chemical
potential in the ultra-relativistic plasma, and Gauss representation of Fermi
functions. Electron chemical potential and number of nucleons per one initial
electron are calculated as functions of and .Comment: 16 pages, 6 figure
The Possibility of Emersion of the Outer Layers in a Massive Star Simultaneously with Iron-Core Collapse: A Hydrodynamic Model
We analyze the behavior of the outer envelope in a massive star during and
after the collapse of its iron core into a protoneutron star (PNS) in terms of
the equations of one-dimensional spherically symmetric ideal hydrodynamics. The
profiles obtained in the studies of the evolution of massive stars up to the
final stages of their existence, immediately before a supernova explosion
(Boyes et al. 1999), are used as the initial data for the distribution of
thermodynamic quantities in the envelope.We use a complex equation of state for
matter with allowances made for arbitrary electron degeneracy and relativity,
the appearance of electron-positron pairs, the presence of radiation, and the
possibility of iron nuclei dissociating into free nucleons and helium nuclei.
We performed calculations with the help of a numerical scheme based on
Godunov's method. These calculations allowed us to ascertain whether the
emersion of the outer envelope in a massive star is possible through the
following two mechanisms: first, the decrease in the gravitational mass of the
central PNS through neutrino-signal emission and, second, the effect of hot
nucleon bubbles, which are most likely formed in the PNS corona, on the
envelope emersion. We show that the second mechanism is highly efficient in the
range of acceptable masses of the nucleon bubbles ()
simulated in our hydrodynamic calculations in a rough, spherically symmetric
approximation.Comment: 14 pages, 11 figure
The Toroidal Iron Atmosphere of a Protoneutron Star: Numerical Solution
A numerical method presented by Imshennik et al. (2002) is used to solve the
two dimensional axisymmetric hydrodynamic problem on the formation of a
toroidal atmosphere during the collapse of an iron stellar core and outer
stellar layers. An evolutionary model from Boyes et al. (1999) with a total
mass of is used as the initial data for the distribution of
thermodynamic quantities in the outer shells of a high-mass star. We analyze in
detail the results of three calculations in which the difference mesh and the
location of the inner boundary of the computational region are varied. In the
initial data, we roughly specify an angular velocity distribution that is
actually justified by the final result - the formation of a hydrostatic
equilibrium toroidal atmosphere with reasonable total mass, , and total angular momentum, , for the two main calculations. We compare the
numerical solution with our previous analytical solution in the form of
toroidal atmospheres (Imshennik and Manukovskii 2000). This comparison
indicates that they are identical if we take into account the more general and
complex equation of state with a nonzero temperature and self-gravitation
effects in the atmosphere. Our numerical calculations, first, prove the
stability of toroidal atmospheres on characteristic hydrodynamic time scales
and, second, show the possibility of sporadic fragmentation of these
atmospheres even after a hydrodynamic equilibrium is established. The
calculations were carried out under the assumption of equatorial symmetry of
the problem and up to relatively long time scales .Comment: 15 pages, 12 figures, 3 table
A Rotating Collapsar and Possible Interpretation of the LSD Neutrino Signal from SN 1987A
We consider an improved rotational mechanism of the explosion of a collapsing
supernova. We show that this mechanism leads to two-stage collapse with a phase
difference of \sim 5 h. Based on this model, we attempt a new interpretation of
the events in underground neutrino detectors on February 23, 1987, related to
the supernova SN 1987A.Comment: 18 pages, 3 figures, 9 table
Flash ionization of the partially ionized wind of the progenitor of SN 1987A
The H II region created by the progenitor of SN 1987A was further heated and
ionized by the supernova flash. Prior to the flash, the temperature of the gas
was 4000 - 5000 K, and helium was neutral, while the post-flash temperature was
only slightly less than 10^5 K, with the gas being ionized to helium-like
ionization stages of C, N and O. We have followed the slow post-flash cooling
and recombination of the gas, as well as its line emission, and find that the
strongest lines are N V 1240 and O VI 1034. Both these lines are good probes
for the density of the gas, and suitable instruments to detect the lines are
STIS on HST and FUSE, respectively. Other lines which may be detectable are N
IV] 1486 and [O III] 5007, though they are expected to be substantially weaker.
The relative strength of the oxygen lines is found to be a good tracer of the
color temperature of the supernova flash. From previous observations, we put
limits on the hydrogen density, n_H, of the H II region. The early N V 1240
flux measured by IUE gives an upper limit which is n_H ~ 180 \eta^{-0.40}
cm^{-3}, where \eta is the filling factor of the gas. The recently reported
emission in [O III] 5007 at 2500 days requires n_H = (160\pm12) \eta^{-0.19}
cm^{-3}, for a supernova burst similar to that in the 500full1 model of Ensman
& Burrows (1992). For the more energetic 500full2 burst the density is n_H =
(215\pm15) \eta^{-0.19} cm^{-3}. These values are much higher than in models of
the X-ray emission from the supernova (n_H ~ 75 cm^{-3}), and it seems
plausible that the observed [O III] emission is produced primarily elsewhere
than in the H II region. We also discuss the type of progenitor consistent with
the H II region. In particular, it seems unlikely that its spectral type was
much earlier than B2 Ia.Comment: LaTeX, 23 pages including 4 figures. To appear in ApJ (Main Journal
Radiation hydrodynamics of SN 1987A: I. Global analysis of the light curve for the first 4 months
The optical/UV light curves of SN 1987A are analyzed with the multi-energy
group radiation hydrodynamics code STELLA. The calculated monochromatic and
bolometric light curves are compared with observations shortly after shock
breakout, during the early plateau, through the broad second maximum, and
during the earliest phase of the radioactive tail. We have concentrated on a
progenitor model calculated by Nomoto & Hashimoto and Saio, Nomoto, & Kato,
which assumes that 14 solar masses of the stellar mass is ejected. Using this
model, we have updated constraints on the explosion energy and the extent of
mixing in the ejecta. In particular, we determine the most likely range of E/M
(explosion energy over ejecta mass) and R_0 (radius of the progenitor). In
general, our best models have energies in the range E = (1.1 +/- 0.3) x 10^{51}
ergs, and the agreement is better than in earlier, flux-limited diffusion
calculations for the same explosion energy. Our modeled B and V fluxes compare
well with observations, while the flux in U undershoots after about 10 days by
a factor of a few, presumably due to NLTE and line transfer effects. We also
compare our results with IUE observations, and a very good quantitative
agreement is found for the first days, and for one IUE band (2500-3000 A) as
long as for 3 months. We point out that the V flux estimated by McNaught &
Zoltowski should probably be revised to a lower value.Comment: 27 pages AASTeX v.4.0 + 35 postscript figures. ApJ, accepte
The neutrino energy and momentum loss through the process in a strong magnetic field
A process of the electron--positron pair production by neutrino propagating
in a strong magnetic field is investigated in the framework of the Standard
Model. The process probability and the mean values of the neutrino energy and
momentum loss are calculated. Possible astrophysical manifestations of the
process considered are briefly analysed.Comment: 8 pages, LATEX, submitted to Physics Letters
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