77,415 research outputs found
Toward an understanding of thermal X-ray emission of pulsars
We present a theoretical model for the thermal X-ray emission and cooling of
isolated pulsars, assuming that pulsars are solid quark stars. We calculate the
heat capacity for such a quark star, and the results show that the residual
thermal energy cannot sustain the observed thermal X-ray luminosities seen in
typical isolated X-ray pulsars. We conclude that other heating mechanisms must
be in operation if the pulsars are in fact solid quark stars. Two possible
heating mechanisms are explored. Firstly, for pulsars with little
magnetospheric activities, accretion from the interstellar medium or from the
material in the associated supernova remnants may power the observed thermal
emission. In the propeller regime, a disk-accretion rate 1% of
the Eddington rate with an accretion onto the stellar surface at a rate of
could explain the observed emission luminosities of the
dim isolated neutron stars and the central compact objects. Secondly, for
pulsars with significant magnetospheric activities, the pulsar spindown
luminosities may have been as the sources of the thermal energy via reversing
plasma current flows. A phenomenological study between pulsar bolometric X-ray
luminosities and the spin energy loss rates presents the probable existence of
a 1/2-law or a linear law, i.e. or
. This result together with the thermal
properties of solid quark stars allow us to calculate the thermal evolution of
such stars. Thermal evolution curves, or cooling curves, are calculated and
compared with the `temperature-age' data obtained from 17 active X-ray pulsars.
It is shown that the bolometric X-ray observations of these sources are
consistent with the solid quark star pulsar model.Comment: Astroparticle Physics Accepte
An alternative non-Markovianity measure by divisibility of dynamical map
Identifying non-Markovianity with non-divisibility, we propose a measure for
non-Markovinity of quantum process. Three examples are presented to illustrate
the non-Markovianity, measure for non-Markovianity is calculated and discussed.
Comparison with other measures of non-Markovianity is made. Our
non-Markovianity measure has the merit that no optimization procedure is
required and it is finite for any quantum process, which greatly enhances the
practical relevance of the proposed measure.Comment: 6 pages, 3 figue
Vibration Powered Radiation of Quaking Magnetar
In juxtaposition with the standard model of rotation powered pulsar, the
model of vibration powered magnetar undergoing quake-induced torsional Alfven
vibrations in its own ultra strong magnetic field experiencing decay is
considered. The presented line of argument suggests that gradual decrease of
frequencies (lengthening of periods) of long-periodic pulsed radiation detected
from a set of X-ray sources can be attributed to magnetic-field-decay induced
energy conversion from seismic vibrations to magneto-dipole radiation of
quaking magnetar.Comment: Text of talk presented at "Mini-Workshop on Pulsars", Nov. 12th,
2010; KIAA-PKU, Beijin
Concurrence of superposition
The bounds on concurrence of the superposition state in terms of those of the
states being superposed are studied in this paper. The bounds on concurrence
are quite different from those on the entanglement measure based on von Neumann
entropy (Phys. Rev. Lett. 97, 100502 (2006)). In particular, a nonzero lower
bound can be provided if the states being superposed are properly constrained.Comment: 4 page
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