Pulsar Electrodynamics: The Relativistic Kinetic Theory of Radiative Plasmas — The Gamma-ray cut-off
da Costa, Antonio Armando, D. A. Diver, E. W. Laing, C. R. Stark, L. F. A. Teodoro
Instituto Superior Técnico, Lisboa, Portugal
15 April, 11:05

The classical modelling of radiation by accelerated charged particles in pulsars predicts a cut-off in photon energy at around 25GeV. Whilst this is broadly consistent with observations, the classical treatment is not self-consistent, and cannot be extended to explain the rare high-energy detections of photons in the 100s of GeV range. In this paper we revisit the theoretical modelling of high-energy radiation processes in very strong electromagnetic fields, in the context of both single particles and collective plasmas, which implies an extension of the Vlasov theory of collisionless plasmas, to take into account radiative processes. There are no classical constraints on this description. We find that there is indeed a critical energy of around 50 GeV that arises naturally in this self-consistent treatment, but rather than being a cut-off, this critical energy signals a transition from radiation that is classical to a quasi-quantum description, in which the particle is able to radiate almost its total energy in a single event. This new modelling therefore places pulsar radiation processes on a more secure physical basis, and admits the possibility of the production of TeV photons in a self-consistent way.

Glitches in the rotation of Pulsars
Espinoza, Cristobal, A.G. Lyne
Jodrell Bank Centre for Astrophysics
15 April, 11:15

A new search for glitches was performed using the Jodrell Bank pulsar timing database, and 104 new glitches were found in the rotation of 64 pulsars. Combining these with those already published we have put together a database containing 315 glitches in 102 pulsars. The database was used to study the glitch activity among the pulsar population, finding that it peaks for pulsars with a characteristic age $\tau \sim 10$ kyr and decreases for longer values of $\tau$, disappearing for objects with $\tau>20$ Myr. Although to a lesser extent, the glitch activity is also lower in the very young pulsars ($\tau \sim 1$ kyr). The cumulative effect of glitches, or the colection of many spin-up events, acts against the regular long-term spindown rate of pulsars. The percentage of the spindown reversed by glitch activity was found to vary between 0.5% and 1.6% for pulsars with a spindown rate between $10^{-14}$ and $3.2 \times 10^{-11}$ Hz s$^{-1}$, decreasing to less than 0.01% towards both higher and lower spindown rates. These ratios are interpreted in terms of the amount of superfluid involved in the generation of glitches. In this context, the activity of the Crab pulsar may be explained by quake-like activity on its crust. Pulsars with low spindown rates seem to exhibit mostly small glitches, matching well the decrease of the amount of superfluid related to glitch activity.

The analysis of glitch sizes indicates that the particular glitching behaviour of PSR J0537-6910 and the Vela pulsar may be shared by most Vela-like pulsars. Most glitches in these objects present the largest frequency and frequency derivative jumps recorded, and seem to occur at regular intervals of time.

A better understanding of the glitching behaviour of pulsars will conduct us towards a more refined knowledge of not only their interiors but also of their spin evolution and gravitational wave emission.

Tests of general relativity and binary evolution studies using pulsar observations
Ferdman, Robert
University of Manchester
15 April, 11:25

A brief review will be given of several predictions of general relativity (GR) that can and have been tested through timing observations of pulsars in binary systems. This will cover, for example, setting limits on dipolar gravitational radiation and on gravitational constant variation, as well as strong-field tests. Also to be discussed, if time permits, is the study of binary system evolution using pulsar observations.

A Bayesian Search For Gravitational Wave Ring-downs Associated With Pulsar Glitches
Heng, Ik Siong, James Clark, Grahama Woan, Matthew Pitkin
University of Glasgow
15 April, 11:35

Glitches in pulsar timing are thought to be associated with sudden changes in the pulsar's angular momentum. A fraction of the excess rotational energy is then radiated away as gravitational wave emission. We present a search for damped-sinusoidal gravitational wave ringdowns using Bayesian model selection. We demonstrate how the result from such a search is easily converted into a statement about the physical properties of the gravitational wave emission.

Carbon atmosphere neutron star in Cassiopeia A: Youngest neutron star in the Galaxy
Ho, Wynn, Craig O. Heinke
University of Southampton
15 April, 11:45

The surface of hot neutron stars is covered by a thin atmosphere. If there is accretion after neutron star formation, the atmosphere could be composed of light elements (H or He); if no accretion takes place or if thermonuclear reactions occur after accretion, heavy elements (e.g., Fe) are expected. Despite detailed searches, observations have been unable to confirm the atmospheric composition of isolated neutron stars. Here we report an analysis of Chandra observations of the X-ray source in the centre of the Cassiopeia A supernova remnant. We show that a carbon atmosphere neutron star produces a good fit to the spectrum. Our emission model, in contrast with others, implies an emission size consistent with theoretical predictions for the radius of neutron stars. This result suggests that there is nuclear burning in the surface layers and also identifies the compact source as the youngest-known (with an age of about 330 years) neutron star in the Galaxy.

Latest HESS observations of Pulsar Wind Nebulae
Keogh, Dominic, HESS Collaboration
Durham University
15 April, 11:55

The confinement of the relativistic outflows of pulsars produces a luminous pulsar wind nebula (PWN) seen across the electromagnetic spectrum. These sources are one of the most prominent classes observed by TeV Cherenkov observatories such as the Namibian based HESS telescopes. Numerous PWN have been observed with HESS, while additional dark sources may represent relic PWN. In this talk I shall outline some of the most exciting recent observations of pulsar wind nebulae with the HESS telescopes.

The optical and infrared counterpart of SGR 0501+4516
Levan, Andrew
University of Warwick
15 April, 12:05

I will present the discovery of the optical/IR counterpart to the soft gamma-repeater SGR 0501+4516. Unlike the majority of magnetars, this one lies in the galactic anticentre direction, and has only moderate extinction, allowing us to search for its counterpart at longer wavelengths. Our comprehensive campaign of observations began only an hour after the first activation of the source, and continued for 14 months. These observations reveal several crucial diagnostics of the IR counterpart of an SGR i) rapid optical/IR variability shows a period almost identical to the X-ray derived period (5.7s), ii) The long term optical/IR variation appears to track that in the X-ray iii) Limits on the proper motion suggest that the spatial velocity is <400 km/s, and show that SGR 0501+4516 is not associated with any supernova remnants, or young stellar clusters, a first for a magnetar.

Surface extraction of electrons in a pulsar
Diver, Declan, A A da Costa, E W Laing, C R Stark, L F A Teodoro
University of Glasgow
15 April, 12:15

We present a novel description of how energetic electrons may be ejected from the pulsar interior into the atmosphere, based on the collective electrostatic oscillations of interior electrons confined to move parallel to the magnetic field. The size of the interior magnetic field influences the interior plasma frequency, via the associated matter density compression. The plasma oscillations occur close to the regions of maximum magnetic field curvature, that is, close to the magnetic poles where the majority of magnetic flux emerges. Given that these oscillations have a density-dependent maximum amplitude before wave-breaking occurs, such waves can eject energetic electrons using only the self-field of the electron population in the interior. Moreover, photons emitted by electrons in the bulk of the oscillation can escape along the field lines by virtue of the lower opacity there (and the fact that they are emitted predominantly in this direction), leading to features in the spectra of pulsars.

The Effelsberg Northern Sky Pulsar Survey
Barr, Ewan
MPIfR Bonn

Pulsars are rapidly rotating neutron stars which emit beams of broadband radio emission from their magnetic poles. The extreme conditions found in and around pulsars make them a fantastic natural laboratory through which many aspects of fundamental physics and astronomy can be probed. As such, modern pulsar surveys provide the means through which we pave the way for new and exciting science. Whether it is an exotic pulsar which pushes the limits of the equation-of-state, a highly accurately timing millisecond pulsar (MSP) that can be used as part of an array to detect gravitational waves or a normal pulsar that will help map the interstellar medium, the discovery of new pulsars inevitably leads to an improvement in our understanding of one or more research areas. Thus we will commence a northern sky blind pulsar survey with the 100-m Effelsberg radio telescope complimented by a twin search of the southern sky with the 64-m Parkes telescope.

Also presented here is PSR J1745+1017, Effelsberg's first ever millisecond pulsar detection, the 18th radio Fermi pulsar so far discovered.

Known pulsars as continuous gravitational wave sources
Pitkin, Matthew
University of Glasgow

Known pulsars are a potential source of continuous gravitational waves and there have been ongoing searches for them within current gravitational wave detector data. No signals have yet been seen, but based on the expected sensitivities of future detectors we examine the potential for detecting them. We examine what kind of star (e.g. strange quark star, hyperon star, or normal neutron star) these objects would have to be to achieve detection. We also study what detections could infer about the strain on the star's crust.

The effect of Gravitational Distortion of Spacetime on Pulsar Timing
Sakai, Satoru, Dr G. Woan, Dr M. Hendry
University of Glasgow

The aim of this research is to determine the impact of gravitational lensing on pulsar timing, and its implications for the detection of gravitational waves. Gravitational lensing occurs when a massive body passes close to the line-of-sight between the Earth and a source. From General Relativity, this causes space-time distortions which result in an extra path length that the light must travel, and subsequently a delay in the time of arrival. This research will look at the rate of change of (gravitational) Shapiro time delay.

Intermittent Radio Emission from PSR B0823+26
Young, Neil, M. Kramer, A. Lyne, B. Stappers, P. Weltevrede
University of Manchester

Intermittent pulsars are characterised by periods, up to years, when their radio emission is off followed by similarly long periods when they are on. They offer a unique insight into magnetospheric physics of pulsars. PSR B0823+26 is a candidate of this pulsar class. Intensive observations of this source were carried out with the Lovell Telescope, at Jodrell Bank, from January to June 2009. This pulsar has subsequently been found to exhibit quasi-periodic radio emission phases, on timescales shorter than that observed in the canonical intermittent pulsar B1931+24. Here, I present the results and analysis of these observations.