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

Pulsar Radio Emission Altitude from Curvature Radiation

We assume that the relativistic sources moving along the dipolar magnetic field lines emit curvature radiation. The beamed emission occurs in the direction of tangents to the field lines, and to receive it, the sight line must align with the tangent within the beaming angle 1/gamma, where gamma is the particle Lorentz factor. By solving the viewing geometry in an inclined and rotating dipole magnetic field, we show that, at any given pulse phase, observer tends to receive radiation only from the specific heights allowed by the geometry. We find outer conal components are emitted at higher altitudes compared to inner components including the core. At any pulse phase, low frequency emission comes from higher altitudes than high frequency emission. We have modeled the emission heights of pulse components of PSR B0329+54, and estimated field line curvature radii and particle Lorentz factors in the emission regions.Comment: 14 pages, 3 figures. Accepted for Astrophysical Journal, 200

Origin of TeV Galactic Cosmic Rays

We consider a possibility of identification of sources of cosmic rays (CR) of the energy above 1 TeV via observation of degree-scale extended gamma-ray emission which traces the locations of recent sources in the Galaxy. Such emission in the energy band above 100 GeV is produced by CR nuclei and electrons released by the sources and spreading into the interstellar medium. We use the data from the Fermi gamma-ray telescope to locate the degree-scale 100 GeV gamma-ray sources. We find that the number of such sources and their overall power match to those expected when CRs injection events happen every ~100 yr in portions of ~1e50 erg. We find that most of the sources are associated to pulsars with spin down age less than ~30 kyr and hence to the recent supernova explosions. This supports the hypothesis of supernova origin of Galactic CRs. We notice that the degree-scale extended emission does not surround shell-like supernova remnants without pulsars. Based on this observation, we argue that the presence of the pulsar is essential for the CR acceleration process. We expect that a significant fraction of the degree-scale sources should be detectable as extended sources with km3-scale neutrino detectors.Comment: 14 pages, 14 figures, accepted for publication in Phys.Rev.

Observations of Non-radial Pulsations in Radio Pulsars

We introduce a model for pulsars in which non-radial oscillations of high spherical degree (l) aligned to the magnetic axis of a spinning neutron star reproduce the morphological features of pulsar beams. In our model, rotation of the pulsar carries a pattern of pulsation nodes underneath our sightline, reproducing the longitude stationary structure seen in average pulse profiles, while the associated time-like oscillations reproduce "drifting subpulses"--features that change their longitude between successive pulsar spins. We will show that the presence of nodal lines can account for observed 180 degree phase jumps in drifting subpulses and their otherwise poor phase stability, even if the time-like oscillations are strictly periodic. Our model can also account for the "mode changes" and "nulls" observed in some pulsars as quasiperiodic changes between pulsation modes of different l or radial overtone n, analogous to pulsation mode changes observed in oscillating white dwarf stars. We will discuss other definitive and testable requirements of our model and show that they are qualitatively supported by existing data. While reserving judgment until the completion of quantitative tests, we are inspired enough by the existing observational support for our model to speculate about the excitation mechanism of the non-radial pulsations, the physics we can learn from them, and their relationship to the period evolution of pulsars.Comment: 28 pages, 9 figures (as separate png files), Astrophysical Journal, in pres

An ecosystem characterisation of the Bay of Bengal

This study summarises the high level drivers on ecological systems of the BOBLME. The ecological characterisation resulted in the identification of 29 subsystems. The report recommends the development of fully integrated approaches that considers human needs and the ecological system, involving stakeholders in a transparent way

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

The Parkes Multibeam Pulsar Survey: PSR J1811-1736 - a pulsar in a highly eccentric binary system

We are undertaking a high-frequency survey of the Galactic plane for radio pulsars, using the 13-element multibeam receiver on the 64-m Parkes radio telescope. We describe briefly the survey system and some of the initial results. PSR J1811-1736, one of the first pulsars discovered with this system, has a rotation period of 104 ms. Subsequent timing observations using the 76-m radio telescope at Jodrell Bank show that it is in an 18.8-day, highly-eccentric binary orbit. We have measured the rate of advance of periastron which indicates a total system mass of 2.6 +- 0.9 Msun, and the minimum companion mass is about 0.7 Msun. This, the high orbital eccentricity and the recycled nature of the pulsar suggests that this system is composed of two neutron stars, only the fourth or fifth such system known in the disk of the Galaxy.Comment: 6 pages, 3 embedded EPS figures, to be published in MNRA

Radio Polarization of the Young High-Magnetic-Field Pulsar PSR J1119-6127

We have investigated the radio polarization properties of PSR J1119-6127, a recently discovered young radio pulsar with a large magnetic field. Using pulsar-gated radio imaging data taken at a center frequency of 2496 MHz with the Australia Telescope Compact Array, we have determined a rotation measure for the pulsar of +842 +/- 23 rad m^-2. These data, combined with archival polarimetry data taken at a center frequency of 1366 MHz with the Parkes telescope, were used to determine the polarization characteristics of PSR J1119-6127 at both frequencies. The pulsar has a fractional linear polarization of ~75% and ~55% at 1366 and 2496 MHz, respectively, and the profile consists of a single, wide component. This pulse morphology and high degree of linear polarization are in agreement with previously noticed trends for young pulsars (e.g., PSR J1513-5908). A rotating-vector (RV) model fit of the position angle (PA) of linear polarization over pulse phase using the Parkes data suggests that the radio emission comes from the leading edge of a conal beam. We discuss PSR J1119-6127 in the context of a recent theoretical model of pulsar spin-down which can in principle be tested with polarization and timing data from this pulsar. Geometric constraints from the RV fit are currently insufficient to test this model with statistical significance, but additional data may allow such a test in the future.Comment: 9 pages, including 6 figures and 1 table. Accepted for publication in Ap

Coherently Dedispersed Polarimetry of Millisecond Pulsars

We present a large sample of high-precision, coherently-dedispersed polarization profiles of millisecond pulsars (MSPs) at frequencies between 410 and 1414 MHz. These data include the first polarimetric observations of several of the pulsars, and the first low-frequency polarization profiles for others. Our observations support previous suggestions that the pulse shapes and polarimetry of MSPs are more complex than those of their slower relatives. An immediate conclusion is that polarimetry-based classification schemes proposed for young pulsars are of only limited use when applied to millisecond pulsars.Comment: 28 pages, 10 figures. Text matches version that appeared in ApJS. Full paper with high-resolution figures available at ftp://ftp.jb.man.ac.uk/pub/psr/papers/msppolpton.ps.g