527 research outputs found
Possible evolution of dim radio quiet neutron star 1E 1207.4-5209 based on a B-decay model
Dim radio-quiet neutron star (DRQNS) 1E 1207.4-5209 is one of the most
heavily examined isolated neutron stars. Wide absorption lines were observed in
its spectrum obtained by both XMM-Newton and Chandra X-ray satellites. These
absorption lines can be interpreted as a principal frequency centered at 0.7
keV and its harmonics at 1.4, 2.1 and possibly 2.8 keV. The principal line can
be formed by resonant proton cyclotron scattering leading to a magnetic field
which is two orders of magnitude larger than the perpendicular component of the
surface dipole magnetic field (B) found from the rotation period (P) and the
time rate of change in the rotation period (\.{P}) of 1E 1207.4-5209. Besides,
age of the supernova remnant (SNR) G296.5+10.0 which is physically connected to
1E 1207.4-5209 is two orders of magnitude smaller than the characteristic age
(=P/2\.{P}) of the neutron star. These huge differences between the
magnetic field values and the ages can be explained based on a B-decay model.
If the decay is assumed to be exponential, the characteristic decay time turns
out to be several thousand years which is three orders of magnitude smaller
than the characteristic decay time of radio pulsars represented in an earlier
work. The lack of detection of radio emission from DRQNSs and the lack of point
sources and pulsar wind nebulae in most of the observed SNRs can also be partly
explained by such a very rapid exponential decay. The large difference between
the characteristic decay times of DRQNSs and radio pulsars must be related to
the differences in the magnetic fields, equation of states and masses of these
isolated neutron stars.Comment: 13 pages, 1 figur
Early phases of different types of isolated neutron star
Two Galactic isolated strong X-ray pulsars seem to be in the densest
environments compared to other types of Galactic pulsar. X-ray pulsar
J1846-0258 can be in an early phase of anomalous X-ray pulsars and soft gamma
repeaters if its average braking index is ~1.8-2.0. X-ray pulsar J1811-1925
must have a very large average braking index (n~11) if this pulsar was formed
by SN 386AD. This X-ray pulsar can be in an early phase of evolution of the
radio pulsars located in the region P~50-150 ms and \.{P}~10
s/s of the P-\.{P} diagram. X-ray/radio pulsar J0540-69 seems to be evolving in
the direction to the dim isolated thermal neutron star region on the P-\.{P}
diagram. Possible progenitors of different types of neutron star are also
discussed.Comment: to appear in the International Journal of Modern Physics
Effects of the background radiation on radio pulsar and supernova remnant searches and the birth rates of these objects
In different directions of the Galaxy the Galactic background radio radiation
and radiation of complex star formation regions which include large number of
OB associations have different influences on radio pulsar (PSR) and supernova
remnant (SNR) searches. In this work we analyse the effects of these background
radiations on the observations of PSRs at 1400 MHz and SNRs at 1000 MHz. In the
interval l=0 the PSRs with flux F0.2 mJy and the SNRs
with surface brightness WmHzsr are
observable for all values of l and b. All the SNRs with
WmHzsr can be observed in the
interval 60l. We have examined samples of PSRs and SNRs to
estimate the birth rates of these objects in the region up to 3.2 kpc from the
Sun and also in the Galaxy. The birth rate of PSRs is about one in 200 years
and the birth rate of SNRs is about one in 65 years in our galaxy.Comment: revised versio
Sturm-Liouville operators on time scales
We establish the connection between Sturm-Liouville equations on time scales
and Sturm--Liouville equations with measure-valued coefficients. Based on this
connection we generalize several results for Sturm-Liouville equations on time
scales which have been obtained by various authors in the past.Comment: 12 page
An integrable discretization of KdV at large times
An "exact discretization" of the Schroedinger operator is considered and its
direct and inverse scattering problems are solved. It is shown that a
differential-difference nonlinear evolution equation depending on two arbitrary
constants can be solved by using this spectral transform and that for a special
choice of the constants it can be considered an integrable discretization of
the KdV equation at large times. An integrable difference-difference equation
is also obtained.Comment: 12 page
Synoptic Sky Surveys and the Diffuse Supernova Neutrino Background: Removing Astrophysical Uncertainties and Revealing Invisible Supernovae
The cumulative (anti)neutrino production from all core-collapse supernovae
within our cosmic horizon gives rise to the diffuse supernova neutrino
background (DSNB), which is on the verge of detectability. The observed flux
depends on supernova physics, but also on the cosmic history of supernova
explosions; currently, the cosmic supernova rate introduces a substantial
(+/-40%) uncertainty, largely through its absolute normalization. However, a
new class of wide-field, repeated-scan (synoptic) optical sky surveys is coming
online, and will map the sky in the time domain with unprecedented depth,
completeness, and dynamic range. We show that these surveys will obtain the
cosmic supernova rate by direct counting, in an unbiased way and with high
statistics, and thus will allow for precise predictions of the DSNB. Upcoming
sky surveys will substantially reduce the uncertainties in the DSNB source
history to an anticipated +/-5% that is dominated by systematics, so that the
observed high-energy flux thus will test supernova neutrino physics. The
portion of the universe (z < 1) accessible to upcoming sky surveys includes the
progenitors of a large fraction (~ 87%) of the expected 10-26 MeV DSNB event
rate. We show that precision determination of the (optically detected) cosmic
supernova history will also make the DSNB into a strong probe of an extra flux
of neutrinos from optically invisible supernovae, which may be unseen either
due to unexpected large dust obscuration in host galaxies, or because some
core-collapse events proceed directly to black hole formation and fail to give
an optical outburst.Comment: 11 pages, 6 figure
A discrete Schrodinger spectral problem and associated evolution equations
A recently proposed discrete version of the Schrodinger spectral problem is
considered. The whole hierarchy of differential-difference nonlinear evolution
equations associated to this spectral problem is derived. It is shown that a
discrete version of the KdV, sine-Gordon and Liouville equations are included
and that the so called `inverse' class in the hierarchy is local. The whole
class of related Darboux and Backlund transformations is also exhibited.Comment: 14 pages, LaTeX2
An Alternative Interpretation of Recent ARPES Measurements on TiSe2
Recently there has been a renewed interest in the charge density wave
transition of TiSe2, fuelled by the possibility that this transition may be
driven by the formation of an excitonic insulator or even an excitonic
condensate. We show here that the recent ARPES measurements on TiSe2 can also
be interpreted in terms of an alternative scenario, in which the transition is
due to a combination of Jahn-Teller effects and exciton formation. The hybrid
exciton-phonons which cause the CDW formation interpolate between a purely
structural and a purely electronic type of transition. Above the transition
temperature, the electron-phonon coupling becomes ineffective but a finite
mean-field density of excitons remains and gives rise to the observed diffuse
ARPES signals.Comment: 4 pages, 2 figure
Approximation of the Sections of the Set of Trajectories of the Control System Described by a Nonlinear Volterra Integral Equation
Approximation of the sections of the set of trajectories of the control system described by a nonlinear Volterra integral equation is studied. The admissible control functions are chosen from the closed ball of the space Lp, p > 1, with radius µ and centered at the origin. The set of admissible control functions is replaced by the set of control functions, which includes a finite number of control functions and generates a finite number of trajectories. It is proved that the sections of the set of trajectories can be approximated by the sections of the set of trajectories, generated by a finite number of control functions
Scattering Theory for Jacobi Operators with Steplike Quasi-Periodic Background
We develop direct and inverse scattering theory for Jacobi operators with
steplike quasi-periodic finite-gap background in the same isospectral class. We
derive the corresponding Gel'fand-Levitan-Marchenko equation and find minimal
scattering data which determine the perturbed operator uniquely. In addition,
we show how the transmission coefficients can be reconstructed from the
eigenvalues and one of the reflection coefficients.Comment: 14 page
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