Detection of Giant Pulses from the Pulsar PSR B0031-07

Giant pulses have been detected from the pulsar PSR B0031-07. A pulse with an intensity higher than the intensity of the average pulse by a factor of 50 or more is encountered approximately once per 300 observed periods. The peak flux density of the strongest pulse is 530 Jy, which is a factor of 120 higher than the peak flux density of the average pulse. The giant pulses are a factor of 20 narrower than the integrated profile and are clustered about its center.Comment: 7 pages, 2 figures, to appear in: Pis'ma v Astronomicheskii Zhurnal, 2004, v.30, No.4, and will be translated as: Astronomy Letters, v.30, No.

No low-frequency turn-over in the spectra of millisecond pulsars

We present the results of the first low frequency measurements of the flux densities of a large sample of millisecond pulsars (MSPs) at 102 and 111 MHz. Combining our observations with data at higher frequencies borrowed from the literature, we constructed the spectra of 30 MSPs in the 0.1 to 4.8 GHz frequency range. Our flux density measurements extend the known spectra of MSPs to the lowest frequency to date. The coverage of a low frequency range allows us to search for low frequency turn-over, which is often observed for normal pulsars. We find that spectra of MSPs differ from those of normal pulsars, showing no low-frequency turn-over typical of normal pulsars. We suggest that the geometry of the radio emission region of MSPs differs from that of normal pulsars: the magnetic field configuration in MSPs' magnetospheres may deviate from that of a pure dipole and/or the radio emission region may be radially compressed. Monochromatic luminosities at this low frequency and the integral luminosity over the 0.1-4.8 GHz frequency range were determined and their dependence on other pulsar parameters analyzed

Correlation of the scattering and dispersion events in the Crab Nebula pulsar

In separate series of observations of the Crab pulsar, pulse broadening due to scattering was measured at 111 MHz, and variations of dispersion due to pulse delay were measured at higher radio frequencies. In a remarkable event lasting 200 days a large increase occurred in both parameters and with similar time signatures. The increases in scattering and dispersion measure observed over the 200 days MJD 53 950-54 150 are attributable to the effects of an ionised cloud or filament crossing the line of sight. The cloud would be $10^{11}{-}10^{12}$ m across, with electron density $10^3{-}10^4$ cm-3. The increased scattering might originate within the cloud itself, or the moving filament might induce turbulence in a separate higher density cloud in the line of sight