J. G. Ables

The radio luminosity distribution of pulsars in 47 Tucanae

We have used the Australia Telescope Compact Array to seek the integrated radio flux from all the pulsars in the core of the globular cluster 47 Tucanae. We have detected an extended region of radio emission and have calibrated its flux against the flux distribution of the known pulsars in the cluster. We find the total 20-cm radio flux from the pulsars in the cluster to be S = 2.0 ± 0.3 mJy. This implies the lower limit to the radio luminosity distribution to be m/n L 1400 = 0.4 mJy kpc 2 and the size of the observable pulsar population to be N? 30.

Coherent Radiation Patterns Suggested by Single-Pulse Observations of a Millisecond Pulsar

We have observed intense radiation spikes from the millisecond pulsar PSR J0437-4715 and find their distribution in pulsar spin phase to be quite unlike the integrated pulse profile. The spikes are observed almost exclusively in a 10° phase window centered on the main pulse. Within that window the phase distribution has a periodic variation, producing a pattern reminiscent of the diffraction fringes associated with coherent emission from a finite aperture. We propose a source model in which the spikes are emitted coherently from a region with spatial scale ≈ 100 m.

Radio Emission of PSR J0437–4715 at 327 MHz

More than 412,000 single pulses from the brightest millisecond radio pulsar PSR J0437-4715 were obtained at 327 MHz using the Ooty Radio Telescope. This pulsar displays neither the nulling nor the systematic drifting phenomenon found in several normal (long period) pulsars. A rigorous upper limit to the percentage of nulling in PSR J0437-4715 is 0.0016%. However, its integrated profile varies on timescales ranging from ≈ 500 periods to days; the variation is slow and unlike the mode-changing phenomenon of normal pulsars. About 3% of the intensity of PSR J0437-4715 varies quasi-periodically, particularly at early pulse phases within the integrated profile. Its fluctuation spectrum has a weak feature at the mean value of 0.253 ± 0.002 cycles per period, with an average rms width of 0.067 ± 0.005 cycles per period, but both parameters vary from phase to phase within the integrated profile, which has not been noticed so far in pulsars. Our results are important to resolve the issue whether the radio emission of millisecond pulsars is similar to that of normal pulsars.

Interstellar Scattering and the Pulse from the Vela Pulsar

Measurements of PSR 0833-45 were made at wavelengths of 21, 48, 73 and 100 cm. Pulse broadening proportional to about the fourth power of the wavelength was found, consistent with multipath scattering in the interstellar medium. It is further concluded that the rotation measure was constant at 33.2 rad m−2 across this wavelength range, supporting the conclusion that the radiation originates in the vicinity of a magnetic pole.