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 $N$ 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 $\sqrt N$ 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 $N$, and the length of time taken until all populations have sizes comparable to $N$ then becomes infinite as $N \to \infty$. Under suitable assumptions, we show that in the early stages of development, up to the time when all populations have sizes at least $N^{1-\alpha}$, for $1/3 < \alpha < 1$, 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