437 research outputs found
Neutrino-electron processes in a dense magnetized plasma
The neutrino-electron scattering in a dense degenerate magnetized plasma
under the conditions is investigated.
The volume density of the neutrino energy and momentum losses due to this
process are calculated. The results we have obtained demonstrate that plasma in
the presence of an external magnetic field is more transparent for neutrino
than non-magnetized plasma. It is shown that neutrino scattering under
conditions considered does not lead to the neutrino force acting on plasma.Comment: 11 pages, LATEX, to be published in Central European Science Journa
QCD vacuum structure in strong magnetic fields
We study the response of the QCD vacuum to strong magnetic fields, using a
potential model for the quark-antiquark interaction. We find that production of
spin-polarized u-ubar pairs is energetically favorable for fields B > B_crit
\sim 10 GeV^2. We contrast the resulting u-ubar condensate with the quark
condensate which is present at zero magnetic field, and we estimate the
corresponding magnetization as a function of B.Comment: 16 pages, LaTeX, 3 eps figures. v2: references added. v3: fixed typ
Our distorted view of magnetars: application of the Resonant Cyclotron Scattering model
The X-ray spectra of the magnetar candidates are customarily fitted with an
empirical, two component model: an absorbed blackbody and a power-law. However,
the physical interpretation of these two spectral components is rarely
discussed. It has been recently proposed that the presence of a hot plasma in
the magnetosphere of highly magnetized neutron stars might distort, through
efficient resonant cyclotron scattering, the thermal emission from the neutron
star surface, resulting in the production of non-thermal spectra. Here we
discuss the Resonant Cyclotron Scattering (RCS) model, and present its XSPEC
implementation, as well as preliminary results of its application to Anomalous
X-ray Pulsars and Soft Gamma-ray Repeaters.Comment: 5 pages, 5 color figures; Astrophysics & Space Science, in press
("Isolated Neutron Stars"; London, UK
High frequency oscillations during magnetar flares
The recent discovery of high frequency oscillations during giant flares from
the Soft Gamma Repeaters SGR 1806-20 and SGR 1900+14 may be the first direct
detection of vibrations in a neutron star crust. If this interpretation is
correct it offers a novel means of testing the neutron star equation of state,
crustal breaking strain, and magnetic field configuration. We review the
observational data on the magnetar oscillations, including new timing analysis
of the SGR 1806-20 giant flare using data from the Ramaty High Energy Solar
Spectroscopic Imager (RHESSI) and the Rossi X-ray Timing Explorer (RXTE). We
discuss the implications for the study of neutron star structure and crust
thickness, and outline areas for future investigation.Comment: 5 pages, 1 figure, to appear in the proceedings of the conference
"Isolated Neutron Stars: from the Interior to the Surface" (April 2006,
London), eds. D. Page, R. Turolla, & S. Zane, Astrophysics & Space Science in
pres
Plasma Magnetosphere Formation Around Oscillating Magnetized Neutron Stars
The notion of death line of rotating pulsars is applied to model of
oscillating neutron stars. It is shown that the magnetosphere of typical
non-rotating oscillating stars may not contain secondary plasma to support the
generation of radio emission in the region of open field lines of plasma
magnetosphere.Comment: Accepted for publication in Astrophysics & Space Scienc
The Anatomy of a Magnetar: XMM Monitoring of the Transient Anomalous X-ray Pulsar XTE J1810-197
We present the latest results from a multi-epoch timing and spectral study of
the Transient Anomalous X-ray Pulsar XTE J1810-197. We have acquired seven
observations of this pulsar with the Newton X-ray Multi-mirror Mission
(XMM-Newton) over the course of two and a half years, to follow the spectral
evolution as the source fades from outburst. The spectrum is arguably best
characterized by a two-temperature blackbody whose luminosities are decreasing
exponentially with tau_1 = 870 days and tau_2 = 280 days, respectively. The
temperatures of these components are currently cooling at a rate of 22% per
year from a nearly constant value recorded at earlier epochs of kT_1 = 0.25 keV
and kT_2 = 0.67 keV, respectively. The new data show that the temperature T_1
and luminosity of that component have nearly returned to their historic
quiescent levels and that its pulsed fraction, which has steadily decreased
with time, is now consistent with the previous lack of detected pulsations in
quiescence. We also summarize the detections of radio emission from XTE
J1810-197, the first confirmed for any AXP. We consider possible models for the
emission geometry and mechanisms of XTE J1810-197.Comment: 8 pages, 7 figures, 1 table, latex. To appear in the proceedings of
"Isolated Neutron Stars", Astrophysics & Space Science, in pres
External Electromagnetic Fields of a Slowly Rotating Magnetized Star with Gravitomagnetic Charge
We study Maxwell equations in the external background spacetime of a slowly
rotating magnetized NUT star and find analytical solutions for the exterior
electric fields after separating the equations of electric field into angular
and radial parts in the lowest order approximation. The star is considered
isolated and in vacuum, with dipolar magnetic field aligned with the axis of
rotation. The contribution to the external electric field of star from the NUT
charge is considered in detail.Comment: 6 pages, 2 figures, accepted for publication in Astrophysics and
Space Scienc
Newborn Magnetars as sources of Gravitational Radiation: constraints from High Energy observations of Magnetar Candidates
Soft Gamma Repeaters and the Anomalous X-ray Pulsars are believed to contain
slowly spinning "magnetars". The enormous energy liberated in the 2004 Dece 27
giant flare from SGR 1806-20, together with the likely recurrence time of such
events, points to an internal magnetic field strength ~ 10^{16} G. Such strong
fields are expected to be generated by a coherent alpha-Omega dynamo in the
early seconds after the Neutron Star formation, if its spin period is of a few
milliseconds at most. A substantial deformation of the NS is caused by such
fields and a newborn millisecond-spinning magnetar would thus radiate for a few
days a strong gravitational wave signal. Such a signal may be detected with
Advanced LIGO-class detectors up to the distance of the Virgo cluster, where ~
1 magnetar per year are expected to form. Recent X-ray observations reveal that
SNRs around magnetar candidates do not show evidence for a larger energy
content than standard SNRs (Vink & Kuiper 2006). This is at variance with what
would be expected if the spin energy of the young, millisecond NS were radiated
away as electromagnetic radiation andd/or relativistic particle winds and,
thus, transferred quickly to the expanding gas shell. We show here that these
recent findings can be reconciled with the idea of magnetars being formed with
fast spins, if most of their initial spin energy is radiated thorugh GWs. In
particular, we find that this occurs for essentially the same parameter range
that would make such objects detectable by Advanced LIGO-class detectors up to
the Virgo Cluster.Comment: Proceedings of the Conference "Isolated Neutron stars: from the
interior to the surface", Eds. D. Page, R. Turolla, S. Zan
Effective Electromagnetic Lagrangian at Finite Temperature and Density in the Electroweak Model
Using the exact propagators in a constant magnetic field, the effective
electromagnetic Lagrangian at finite temperature and density is calculated to
all orders in the field strength B within the framework of the complete
electroweak model, in the weak coupling limit. The partition function and free
energy are obtained explicitly and the finite temperature effective coupling is
derived in closed form. Some implications of this result, potentially
interesting to astrophysics and cosmology, are discussed.Comment: 14 pages, Revtex
Short Gamma Ray Bursts as possible electromagnetic counterpart of coalescing binary systems
Coalescing binary systems, consisting of two collapsed objects, are among the
most promising sources of high frequency gravitational waves signals
detectable, in principle, by ground-based interferometers. Binary systems of
Neutron Star or Black Hole/Neutron Star mergers should also give rise to short
Gamma Ray Bursts, a subclass of Gamma Ray Bursts. Short-hard-Gamma Ray Bursts
might thus provide a powerful way to infer the merger rate of two-collapsed
object binaries. Under the hypothesis that most short Gamma Ray Bursts
originate from binaries of Neutron Star or Black Hole/Neutron Star mergers, we
outline here the possibility to associate short Gamma Ray Bursts as
electromagnetic counterpart of coalescing binary systems.Comment: 4 pages, 1 figur
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