711 research outputs found
Subsonic propellers in a strong wind as anomalous X-ray pulsars
The appearance of subsonic propellers situated in a strong wind is discussed.
We show that it is similar to the appearance of anomalous X-ray pulsars (AXPs)
provided the mass and the magnetic moment of neutron stars are 1.4 solar
masses, and 2E+30 G cm^3, respectively, and the strength of the wind is M_c =
3E+17 g/s. Under these conditions, the spin periods of subsonic propellers are
limited within the range of 5-15 s, and the expected spin-down rates are close
to 7E-11 s/s. The mass accretion rate onto the stellar surface is limited to
the rate of plasma penetration into its magnetosphere at the boundary. As this
process is governed by the reconnection of the field lines, the accretion rate
onto the stellar surface constitutes 1-2% of M_c. In this case the X-ray
luminosity of the objects under consideration can be evaluated as 4E+35 erg/s.
The model predicts the existence of at least two spatially separated sources of
the X-ray emission: hot spots at the stellar surface, and the hot atmosphere
surrounding the magnetosphere of the star. The ages of the subsonic propellers
under the conditions of interest are limited to 10^5 yr.Comment: 5 pages, 1 figure, accepted for publication in A&
Relativistic Particle Acceleration in a Folded Current Sheet
Two-dimensional particle simulations of a relativistic Harris current sheet
of pair plasmashave demonstrated that the system is unstable to the
relativistic drift kink instability (RDKI) and that a new kind of acceleration
process takes place in the deformed current sheet. This process contributes to
the generation of non-thermal particles and contributes to the fast magnetic
dissipation in the current sheet structure. The acceleration mechanism and a
brief comparison with relativistic magnetic reconnection are presented.Comment: 11 preprint pages, including 3 .eps figure
Green Bank Telescope Observations of the Eclipse of Pulsar "A" in the Double Pulsar Binary PSR J0737-3039
We report on the first Green Bank Telescope observations at 427, 820 and 1400
MHz of the newly discovered, highly inclined and relativistic double pulsar
binary. We focus on the brief eclipse of PSR J0737-3039A, the faster pulsar,
when it passes behind PSR J0737-3039B. We measure a frequency-averaged eclipse
duration of 26.6 +/- 0.6 s, or 0.00301 +/- 0.00008 in orbital phase. The
eclipse duration is found to be significantly dependent on radio frequency,
with eclipses longer at lower frequencies. Specifically, eclipse duration is
well fit by a linear function having slope (-4.52 +/- 0.03) x 10^{-7}
orbits/MHz. We also detect significant asymmetry in the eclipse. Eclipse
ingress takes 3.51 +/- 0.99 times longer than egress, independent of radio
frequency. Additionally, the eclipse lasts (40 +/- 7) x 10^{-5} in orbital
phase longer after conjunction, also independent of frequency. We detect
significant emission from the pulsar on short time scales during eclipse in
some orbits. We discuss these results in the context of a model in which the
eclipsing material is a shock-heated plasma layer within the slower PSR
J0737-3039B's light cylinder, where the relativistic pressure of the faster
pulsar's wind confines the magnetosphere of the slower pulsar.Comment: 12 pages, 3 figure
Thermal Cyclotron Reprocessing of Gammy-Ray Bursts - Theory and Model Spectra
We examine the generation of infrared, optical, and ultraviolet flashes from single, magnetized neutron stars are experiencing of gamma-ray burst. Cyclotron reprocessing of energetic gamma-ray burst photons in the neutron star magnetosphere is assumed to be the underlying mechanism reponsible for the display at longer wavelengths, and thermal equilibrium is assumed in order to calculate electron distribution function. It is shown that thesea good approximations for a wide range of conditions expected in neutron star magnetospheres. The thermal cycoltron model proves capable fo generating ptical outbursts similar to bright historical events. althrough opitcal transients most likely would be much fainter. For a wide range of conditions the model predicts bright, nondelayed flashes, extending in some cases even beyond the ultraviolet. Since the emission at long wavelengths is correlated with the gammar-rays down to time scales small compared with the burst duration, time-averaged spectra are calculated corresponding to the time-averaged gamma-ray burst spectrum. For flashes that do not exhibit a spectral turnover in the optical region, Lopt α Bas with α ~ 3/4, so that optical transients could be used to constrain the magnetic field strength and distance of gamma-ray burst sources. The long-wavelength fluxes for the recently discovered soft repearing source SGR 1806-20 are also estimated
The Double Pulsar Eclipses I: Phenomenology and Multi-frequency Analysis
The double pulsar PSR J0737-3039A/B displays short, 30 s eclipses that arise
around conjunction when the radio waves emitted by pulsar A are absorbed as
they propagate through the magnetosphere of its companion pulsar B. These
eclipses offer a unique opportunity to probe directly the magnetospheric
structure and the plasma properties of pulsar B. We have performed a
comprehensive analysis of the eclipse phenomenology using multi-frequency radio
observations obtained with the Green Bank Telescope. We have characterized the
periodic flux modulations previously discovered at 820 MHz by McLaughlin et
al., and investigated the radio frequency dependence of the duration and depth
of the eclipses. Based on their weak radio frequency evolution, we conclude
that the plasma in pulsar B's magnetosphere requires a large multiplicity
factor (~ 10^5). We also found that, as expected, flux modulations are present
at all radio frequencies in which eclipses can be detected. Their complex
behavior is consistent with the confinement of the absorbing plasma in the
dipolar magnetic field of pulsar B as suggested by Lyutikov & Thompson and such
a geometric connection explains that the observed periodicity is harmonically
related to pulsar B's spin frequency. We observe that the eclipses require a
sharp transition region beyond which the plasma density drops off abruptly.
Such a region defines a plasmasphere which would be well inside the
magnetospheric boundary of an undisturbed pulsar. It is also two times smaller
than the expected standoff radius calculated using the balance of the wind
pressure from pulsar A and the nominally estimated magnetic pressure of pulsar
B.Comment: 9 pages, 7 figures, 3 tables, ApJ in pres
Large frequency drifts during Type I X-ray bursts
We study the spin-down of a neutron star atmosphere during the Type I X-ray
burst in low mass X-ray binaries. Using polar cap acceleration models, we show
that the resulting stellar ``wind'' torque on the burning shell due to the
flowing charged particles (electrons, protons and ions) from the star's polar
caps may change the shell's angular momentum during the burst. We conclude that
the net change in the angular momentum of the star's atmosphere can account for
rather large frequency drifts observed during Type I X-ray burst.Comment: 8 pages, more discussion adde
Time Variability in the X-ray Nebula Powered by Pulsar B1509-58
We use new and archival Chandra and ROSAT data to study the time variability
of the X-ray emission from the pulsar wind nebula (PWN) powered by PSR B1509-58
on timescales of one week to twelve years. There is variability in the size,
number, and brightness of compact knots appearing within 20" of the pulsar,
with at least one knot showing a possible outflow velocity of ~0.6c (assuming a
distance to the source of 5.2 kpc). The transient nature of these knots may
indicate that they are produced by turbulence in the flows surrounding the
pulsar. A previously identified prominent jet extending 12 pc to the southeast
of the pulsar increased in brightness by 30% over 9 years; apparent outflow of
material along this jet is observed with a velocity of ~0.5c. However, outflow
alone cannot account for the changes in the jet on such short timescales.
Magnetohydrodynamic sausage or kink instabilities are feasible explanations for
the jet variability with timescale of ~1.3-2 years. An arc structure, located
30"-45" north of the pulsar, shows transverse structural variations and appears
to have moved inward with a velocity of ~0.03c over three years. The overall
structure and brightness of the diffuse PWN exterior to this arc and excluding
the jet has remained the same over the twelve year span. The photon indices of
the diffuse PWN and possibly the jet steepen with increasing radius, likely
indicating synchrotron cooling at X-ray energies.Comment: accepted to ApJ, 14 pages, 8 figure
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