1,886 research outputs found
Red Noise in Anomalous X-ray Pulsar Timing Residuals
Anomalous X-ray Pulsars (AXPs), thought to be magnetars, exhibit poorly
understood deviations from a simple spin-down called "timing noise". AXP timing
noise has strong low-frequency components which pose significant challenges for
quantification. We describe a procedure for extracting two quantities of
interest, the intensity and power spectral index of timing noise. We apply this
procedure to timing data from three sources: a monitoring campaign of five
AXPs, observations of five young pulsars, and the stable rotator PSR B1937+21.Comment: submitted to the proceedings of the "40 Years of Pulsars" conferenc
A Search for Single Radio Pulses and Bursts from Southern AXPs
We observed four southern AXPs in 1999 near 1400 MHz with the Parkes 64-m
radio telescope to search for periodic radio emission. No Fourier candidates
were discovered in the initial analysis, but the recent radio activity observed
for the AXP XTE J1810-197 has prompted us to revisit these data to search for
single radio pulses and bursts. The data were searched for both persistent and
bursting radio emission at a wide range of dispersion measures, but no
detections of either kind were made. These results further weaken the proposed
link between rotating radio transient sources and magnetars. However, continued
radio searches of these and other AXPs at different epochs are warranted given
the transient nature of the radio emission seen from XTE J1810-197, which until
very recently was the only known radio-emitting AXP.Comment: 3 pages, including 1 table. To appear in the proceedings of "40 Years
of Pulsars: Millisecond Pulsars, Magnetars, and More", August 12-17, 2007,
McGill University, Montreal, Canad
An axisymmetric hydrodynamical model for the torus wind in AGN. III: Spectra from 3D radiation transfer calculations
We calculate a series of synthetic X-ray spectra from outflows originating
from the obscuring torus in active galactic nuclei (AGN). Such modeling
includes 2.5D hydrodynamical simulations of an X-ray excited torus wind,
including the effects of X-ray heating, ionization, and radiation pressure. 3D
radiation transfer calculations are performed in the 3D Sobolev approximation.
Synthetic X-ray line spectra and individual profiles of several strong lines
are shown at different inclination angles, observing times, and for different
characteristics of the torus.
Our calculations show that rich synthetic warm absorber spectra from 3D
modeling are typically observed at a larger range of inclinations than was
previously inferred from simple analysis of the transmitted spectra. In
general, our results are supportive of warm absorber models based on the
hypothesis of an "X-ray excited funnel flow" and are consistent with
characteristics of such flows inferred from observations of warm absorbers from
Seyfert 1 galaxies.Comment: 31 pages, 10 figure
XMM-Newton X-ray Observation of the High-Magnetic-Field Radio Pulsar PSR J1734--3333
Using observations made with the XMM-Newton Observatory, we report the
probable X-ray detection of the high-magnetic-field radio pulsar PSR
J1734-3333. This pulsar has an inferred surface dipole magnetic field of B =
5.2e13 G, just below that of one anomalous X-ray pulsar (AXP). We find that the
pulsar has an absorbed 0.5-2.0 keV flux of (5-15)e-15 erg/s/cm^2 and that its
X-ray luminosity L_X is well below its spin down luminosity E_dot, with L_X <
0.1E_dot. No pulsations were detected in these data although our derived upper
limit is unconstraining. Like most of the other high-B pulsars, PSR J1734-3333
is X-ray faint with no sign of magnetar activity. We collect and tabulate the
properties of this and all other known high-B radio pulsars with measured X-ray
luminosities or luminosity upper limits and plot L_X versus B for them all.Comment: 14 pages, 2 tables, 3 figures, published in the Astrophysical
Journal. Includes updated Figure
Escape from the boundary in Markov population processes
Density dependent Markov population processes in large populations of size
were shown by Kurtz (1970, 1971) to be well approximated over finite time
intervals by the solution of the differential equations that describe their
average drift, and to exhibit stochastic fluctuations about this deterministic
solution on the scale that can be approximated by a diffusion
process. Here, motivated by an example from evolutionary biology, we are
concerned with describing how such a process leaves an absorbing boundary.
Initially, one or more of the populations is of size much smaller than , and
the length of time taken until all populations have sizes comparable to
then becomes infinite as . Under suitable assumptions, we show
that in the early stages of development, up to the time when all populations
have sizes at least , for , the process can be
accurately approximated in total variation by a Markov branching process.
Thereafter, the process is well approximated by the deterministic solution
starting from the original initial point, but with a random time delay.
Analogous behaviour is also established for a Markov process approaching an
equilibrium on a boundary, where one or more of the populations become extinct.Comment: 50 page
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