Radio Observations of Two Isolated Neutron Stars, RXJ0720.4-3125 and RX J0806.4-4132

Radio observations of two isolated neutron stars, RXJ0720.4-3125 and RX J0806.4-4132, have been made with the Australia Telescope Compact Array at a frequency of 1.4 GHz. No continuum emission is detected from either object with a 3 sigma upper limit of 0.2 mJy. The data were also folded synchronously with the known rotation periods of 8.4 and 11.4 s respectively. No pulsed emission was detected. If the pulse duty cycle is small, the upper limit on pulsed emission can be reduced still further to 0.04 mJy. The best evidence seems to indicate that the isolated neutron stars detected by ROSAT all-sky survey are relatively young objects, born with a very high magnetic field.Comment: Accepted for publication in MNRAS. 4 pages, 4 figure

Pulsar Braking Indices Revisited

Using the standard equation for the slowdown of a neutron star, we derive a formula for the braking index via integration rather than the conventional differentiation. The new formula negates the need to measure the second time derivative of the rotation frequency. We show that the method gives similar braking indices for PSR B1509-58 and the Crab pulsar to those already in the literature. We point out that our method is useful for obtaining the braking indices of moderate aged pulsars without the need for long, phase-connected timing solutions. We applied the method to 20 pulsars and discuss the implications of the results. We find that virtually all the derived braking indices are dominated by the effects of (unseen) glitches, the recovery from which corrupts the value of the frequency first derivative. However, any real, large, positive braking index has implications for magnetic field decay and offers support to recent models of pulsar evolution.Comment: 5 pages, 2 figures, 1 table, accepted by MNRA

Pulsar braking and the P-Pdot diagram

The location of radio pulsars in the period-period derivative (P-Pdot) plane has been a key diagnostic tool since the early days of pulsar astronomy. Of particular importance is how pulsars evolve through the P-Pdot diagram with time. Here we show that the decay of the inclination angle (alpha-dot) between the magnetic and rotation axes plays a critical role. In particular, alpha-dot strongly impacts on the braking torque, an effect which has been largely ignored in previous work. We carry out simulations which include a negative alpha-dot term, and show that it is possible to reproduce the observational P-Pdot diagram without the need for either pulsars with long birth periods or magnetic field decay. Our best model indicates a birth rate of 1 radio pulsar per century and a total Galactic population of ~20000 pulsars beaming towards Earth.Comment: 9 pages, 5 figures, accepted by MNRA

Single Dish Polarization Calibration

Using the formalism of Hamaker et al. (1996), I derive a method for the polarization calibration of observations made with a single radio telescope. This method is particularly appropriate for observations of pulsars, where the sign and magnitude of the circular polarization are useful for understanding the emission processes at work. I apply the method to observations of PSR J1359-6038 made using the multibeam receiver on the Parkes radio telescope.Comment: Accepted by PASA. 11 pages. 3 figure

Profile morphology and polarization of young pulsars

We present polarization profiles at 1.4 and 3.1 GHz for 14 young pulsars with characteristic ages less than 75 kyr. Careful calibration ensures that the absolute position angle of the linearly polarized radiation at the pulsar is obtained. In combination with previously published data we draw three main conclusions about the pulse profiles of young pulsars. (1) Pulse profiles are simple and consist of either one or two prominent components. (2) The linearly polarized fraction is nearly always in excess of 70 per cent. (3) In profiles with two components the trailing component nearly always dominates, only the trailing component shows circular polarization and the position angle swing is generally flat across the leading component and steep across the trailing component. Based on these results we can make the following generalisations about the emission beams of young pulsars. (1) There is a single, relatively wide cone of emission from near the last open field lines. (2) Core emission is absent or rather weak. (3) The height of the emission is between 1 and 10 per cent of the light cylinder radius.Comment: Accepted for publication in MNRAS. 16 page

Giant Pulses from the Millisecond Pulsar B1821-24

We have carried out a survey for `giant pulses' in 5 millisecond pulsars. We detect individual pulses from the high Edot pulsar PSR B1821-24 with energies exceeding 50x the mean pulse energy. These giant pulses are concentrated in a narrow phase window coincident with the power-law non-thermal pulse seen in hard X-rays. This is the third example of the giant pulse phenomenon. It supports the idea that large B fields in the outer magnetosphere are critical to the formation of such pulses and further suggests a direct connection between giant pulses and high energy emission.Comment: 6pp, 3 figures. To Appear in ApJ Letters, Vol 55

School segregation in multi-ethnic England

Aspects of both educational development and multi-cultural inter-relationships are frequently related to school ethnic composition, with arguments that ethnically segregated schools both retard the development of multi-ethnic understanding and influence educational performance. In this paper, we employ data on their ethnic composition to portray the extent of segregation in English secondary schools in 2001, using a novel graphical method to explore its nature and spatial variation. We find substantial segregation on ethnic criteria in some places. Nevertheless, over the country as a whole, attendance at substantially mono-ethnic schools is not the norm for members of the non-white groups (though it is for whites in many areas). Half of all non-white secondary students in England attended schools where more than 75 per cent of the total enrolment comprised whites.ethnicity, segregation, schools, spatial concentration, England