2,293 research outputs found
Mechanical Model for Relativistic Blast Waves
Relativistic blast waves can be described by a mechanical model. In this
model, the "blast" -- the compressed gas between the forward and reverse shocks
-- is viewed as one hot body. Equations governing its dynamics are derived from
conservation of mass, energy, and momentum. Simple analytical solutions are
obtained in the two limiting cases of ultra-relativistic and non-relativistic
reverse shock. Equations are derived for the general explosion problem.Comment: 8 pages, accepted to ApJ Letter
Electron Transport Properties of Composite Ferroelectrics
We study electron transport in composite ferroelectrics --- materials
consisting of metallic grains embedded in a ferroelectric matrix. Due to its
complex tunable morphology the thermodynamic properties of these materials can
be essentially different from bulk or thin-film ferroelectrics. We calculate
the conductivity of composite ferroelectrics by taking into account the
interplay between charge localization, multiple grain boundaries, strong
Coulomb repulsion, and ferroelectric order parameter. We show that the
ferroelectricity plays a crucial role on the temperature behavior of the
conductivity in the vicinity of the ferroelectric-paraelectric transition.Comment: 6 pages, 3 figure
Inertia of Heat in Advective Accretion Disks around Kerr Black Holes
In the innermost region of the advective accretion disk orbiting a black hole
of high spin, the inertia of heat stored in the accreting gas is comparable to
that of the gas rest mass itself. Accounting for this effect, we derive
additional terms in the disk structure equations, and show that the heat
inertia plays a significant role in the global energy conservation and dynamics
of accretion in the relativistic advective disks.Comment: 6 pages, Latex, submitted to ApJ
Estimates for Lorentz factors of gamma-ray bursts from early optical afterglow observations
The peak time of optical afterglow may be used as a proxy to constrain the
Lorentz factor Gamma of the gamma-ray burst (GRB) ejecta. We revisit this
method by including bursts with optical observations that started when the
afterglow flux was already decaying; these bursts can provide useful lower
limits on Gamma. Combining all analyzed bursts in our sample, we find that the
previously reported correlation between Gamma and the burst luminosity L_gamma
does not hold. However, the data clearly shows a lower bound Gamma_min which
increases with L_gamma. We suggest an explanation for this feature: explosions
with large jet luminosities and Gamma < Gamma_min suffer strong adiabatic
cooling before their radiation is released at the photosphere; they produce
weak bursts, barely detectable with present instruments. To test this
explanation we examine the effect of adiabatic cooling on the GRB location in
the L_gamma - Gamma plane using a Monte Carlo simulation of the GRB population.
Our results predict detectable on-axis "orphan" afterglows. We also derive
upper limits on the density of the ambient medium that decelerates the
explosion ejecta. We find that the density in many cases is smaller than
expected for stellar winds from normal Wolf-Rayet progenitors. The burst
progenitors may be peculiar massive stars with weaker winds or there might
exist a mechanism that reduces the stellar wind a few years before the
explosion.Comment: 24 pages, 7 figures, 2 tables, accepted for publication in Ap
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