6,152 research outputs found
Radiation spectra and polarization in magnetar bursts
We present Monte Carlo simulations of radiative transfer in magnetar
atmospheres. We include the effects of vacuum polarization, electron and proton
scattering, and free-free absorption. Simulations are performed for the
atmosphere model with the magnetic field perpendicular and also tilted with
respect to the neutron star surface, and we show that the average spectrum does
not strongly depend on the orientation of the magnetic field. We investigate
the region of the parameter space where the vacuum absorption-like feature
appears in the spectrum and we analyze the shape of the proton cyclotron line.
Our results indicate that the existence of the vacuum polarization feature
should be a general attribute of soft gamma-ray repeaters burst spectra,
provided that the energy release takes place at the sufficiently dense region,
and the atmosphere scaleheight is large enough. We discuss the existence of
such a feature in recent observational data on these sources.Comment: submitted to Ap
Chandra observations of the old pulsar PSR B1451-68
We present 35 ks Chandra ACIS observations of the 42 Myr old radio pulsar PSR
B1451-68. A point source is detected 0.32" +/- 0.73" from the expected radio
pulsar position. It has ~200 counts in the 0.3-8 keV energy range. We identify
this point source as the X-ray counterpart of the radio pulsar. PSR B1451-68 is
located close to a 2MASS point source, for which we derive 7% as the upper
limit on the flux contribution to the measured pulsar X-ray flux. The pulsar
spectrum can be described by either a power-law model with photon index
Gamma=2.4 (+0.4/-0.3) and a unrealistically high absorbing column density N(H)=
(2.5 (+1.2/-1.3)) * 10^(21) cm^-2, or by a combination of a kT=0.35
(+0.12/-0.07) keV blackbody and a Gamma = 1.4 +/- 0.5 power-law component for
N(H)[DM]= 2.6 * 10^(20) cm^-2, estimated from the pulsar dispersion measure. At
the parallactic, Lutz-Kelker bias corrected distance of 480 pc, the non-thermal
X-ray luminosities in the 0.3-8 keV energy band are either Lx(nonth)= (11.3 +/-
1.7) * 10^(29) erg/s or Lx(nonth)= (5.9 (+4.9/-5.0)) * 10^(29) erg/s,
respectively. This corresponds to non-thermal X-ray efficiencies of either
eta(nonth)= Lx(nonth) / (dE/dt) ~ 0.005 or 0.003, respectively.Comment: 19 pages, 9 figures, 2 tables, accepted by Ap
Photon assisted tunneling in pairs of silicon donors
Shallow donors in silicon are favorable candidates for the implementation of solid-state quantum computer architectures because of the promising combination of atomiclike coherence properties and scalability from the semiconductor manufacturing industry. Quantum processing schemes require (among other things) controlled information transfer for readout. Here we demonstrate controlled electron tunneling at 10 K from P to Sb impurities and vice versa with the assistance of resonant terahertz photons
Space-Time Description of Scalar Particle Creation by a Homogeneous Isotropic Gravitational Field
We give the generalization of the method of the space-time description of
particle creation by a gravitational field for a scalar field with nonconformal
coupling to the curvature. The space-time correlation function is obtained for
a created pair of the quasi-particles, corresponding to a diagonal form of the
instantaneous Hamiltonian. The case of an adiabatic change of the metric of
homogeneous isotropic space is analyzed. We show that the created pairs of
quasi-particles in de Sitter space should be interpreted as pairs of virtual
particles.Comment: 7 pages, 3 figure
Boundary condition at the junction
The quantum graph plays the role of a solvable model for a two-dimensional
network. Here fitting parameters of the quantum graph for modelling the
junction is discussed, using previous results of the second author.Comment: Replaces unpublished draft on related researc
- …