On the Excess Dispersion in the Polarization Position Angle of Pulsar Radio Emission

The polarization position angles (PA) of pulsar radio emission occupy a distribution that can be much wider than what is expected from the average linear polarization and the off-pulse instrumental noise. Contrary to our limited understanding of the emission mechanism, the excess dispersion in PA implies that pulsar PAs vary in a random fashion. An eigenvalue analysis of the measured Stokes parameters is developed to determine the origin of the excess PA dispersion. The analysis is applied to sensitive, well-calibrated polarization observations of PSR B1929+10 and PSR B2020+28. The analysis clarifies the origin of polarization fluctuations in the emission and reveals that the excess PA dispersion is caused by the isotropic inflation of the data point cluster formed by the measured Stokes parameters. The inflation of the cluster is not consistent with random fluctuations in PA, as might be expected from random changes in the orientation of the magnetic field lines in the emission region or from stochastic Faraday rotation in either the pulsar magnetosphere or the interstellar medium. The inflation of the cluster, and thus the excess PA dispersion, is attributed to randomly polarized radiation in the received pulsar signal. The analysis also indicates that orthogonal polarization modes (OPM) occur where the radio emission is heavily modulated. In fact, OPM may only occur where the modulation index exceeds a critical value of about 0.3.Comment: Accepted for publication in Ap

Birth and Evolution of Isolated Radio Pulsars

We investigate the birth and evolution of Galactic isolated radio pulsars. We begin by estimating their birth space velocity distribution from proper motion measurements of Brisken et al. (2002, 2003). We find no evidence for multimodality of the distribution and favor one in which the absolute one-dimensional velocity components are exponentially distributed and with a three-dimensional mean velocity of 380^{+40}_{-60} km s^-1. We then proceed with a Monte Carlo-based population synthesis, modelling the birth properties of the pulsars, their time evolution, and their detection in the Parkes and Swinburne Multibeam surveys. We present a population model that appears generally consistent with the observations. Our results suggest that pulsars are born in the spiral arms, with a Galactocentric radial distribution that is well described by the functional form proposed by Yusifov & Kucuk (2004), in which the pulsar surface density peaks at radius ~3 kpc. The birth spin period distribution extends to several hundred milliseconds, with no evidence of multimodality. Models which assume the radio luminosities of pulsars to be independent of the spin periods and period derivatives are inadequate, as they lead to the detection of too many old simulated pulsars in our simulations. Dithered radio luminosities proportional to the square root of the spin-down luminosity accommodate the observations well and provide a natural mechanism for the pulsars to dim uniformly as they approach the death line, avoiding an observed pile-up on the latter. There is no evidence for significant torque decay (due to magnetic field decay or otherwise) over the lifetime of the pulsars as radio sources (~100 Myr). Finally, we estimate the pulsar birthrate and total number of pulsars in the Galaxy.Comment: 27 pages, including 15 figures, accepted by Ap

Anomalous scattering of highly dispersed pulsars

We report multifrequency measurements of scatter broadening times for nine highly dispersed pulsars over a wide frequency range (0.6 -- 4.9 GHz). We find the scatter broadening times to be larger than expected and to scale with frequency with an average power-law index of $3.44\pm 0.13$, i.e. significantly less than that expected from standard theories. Such possible discrepancies have been predicted very recently by Cordes & Lazio.Comment: 7 pages, 4 figures, accepted for publication in ApJ Letter

PSR J2229+6114: Discovery of an Energetic Young Pulsar in the Error Box of the EGRET Source 3EG J2227+6122

We report the detection of radio and X-ray pulsations at a period of 51.6 ms from the X-ray source RX/AX J2229.0+6114 in the error box of the EGRET source 3EG J2227+6122. An ephemeris derived from a single ASCA observation and multiple epochs at 1412 MHz from Jodrell Bank indicates steady spin-down with P-dot = 7.83 x 10^(-14) s/s. From the measured P and P-dot we derive spin-down power E-dot = 2.2 x 10^(37) erg/s, magnetic field B = 2.0 x 10^(12) G, and characteristic age P/2P-dot = 10,460 yr. An image from the Chandra X-ray Observatory reveals a point source surrounded by centrally peaked diffuse emission that is contained within an incomplete radio shell. We assign the name G106.6+2.9 to this new supernova remnant, which is evidently a pulsar wind nebula. For a distance of 3 kpc estimated from X-ray absorption, the ratio of X-ray luminosity to spin-down power is ~8 x 10^(-5), smaller than that of most pulsars, but similar to the Vela pulsar. If PSR J2229+6114 is the counterpart of 3EG J2227+6122 then its efficiency of gamma-ray production, if isotropic, is 0.016 (d/3 kpc)^2. It obeys an established trend of gamma-ray efficiency among known gamma-ray pulsars which, in combination with the demonstrated absence of any other plausible counterpart for 3EG J2227+6122, makes the identification compelling. If confirmed, this identification bolsters the pulsar model for unidentified Galactic EGRET sources.Comment: 5 pages, 4 figures, accepted by The Astrophysical Journal Letter

Anomalous Axion Interactions and Topological Currents in Dense Matter

Recently an effective Lagrangian for the interactions of photons, Nambu-Goldstone bosons and superfluid phonons in dense quark matter has been derived using anomaly matching arguments. In this paper we illuminate the nature of certain anomalous terms in this Lagrangian by an explicit microscopic calculation. We also generalize the corresponding construction to introduce the axion field. We derive an anomalous axion effective Lagrangian describing the interactions of axions with photons and superfluid phonons in the dense matter background. This effective Lagrangian, among other things, implies that an axion current will be induced in the presence of magnetic field. We speculate that this current may be responsible for the explanation of neutron star kicks.Comment: 10 page

|V|: New insight into the circular polarization of radio pulsars

We present a study of single pulses from nine bright northern pulsars to investigate the behaviour of circular polarisation, V. The observations were conducted with the Effelsberg 100-m radio telescope at 1.41 GHz and 4.85 GHz and the Westerbork radio telescope at 352 MHz. For the first time, we present the average profile of the absolute circular polarisation |V| in the single pulses. We demonstrate that the average profile of |V| is the distinguishing feature between pulse components that exhibit low V in the single pulses and components that exhibit high V of either handedness, despite both cases resulting in a low mean. We also show that the |V| average profile remains virtually constant with frequency, which is not generally the case for V, leading us to the conclusion that |V| is a key quantity in the pulsar emission problem.Comment: 5 pages, accepted for publication in MNRAS letter