Radio Pulse Shapes, Flux Densities, and Dispersion of Pulsar NP 0532

Observations of NP 0532 at frequencies between 65 and 611 MHz are reported. At high frequencies the main pulse is found to be double; the second component and the interpulse are of very short duration (<300 sec) at 430 MHz. At lower frequencies the pulses become progressively broader until, below about 120 MHz, only one broad pulse is observed. Measurements of the pulsed flux density yield a spectral index of -2.9 + 0.4 above 150 MHz, but a sharp turnover in the spectrum occurs at about 100 MHz. The law of pulse delay as a function of frequency agrees closely with the tenuous-plasma dispersion relation, and an improved value of the dispersion measure is given The variation with radiofrequency of the pulse shape and the low-frequency turnover of the pulsed flux density are explained as effects of scattering in the ionized interstellar medium, if one assumes frequency-independent pulse shape and constant spectral index of the source itself. The compact source observed at low frequencies in the Crab Nebula may be the pulsar.