The Characteristics of Millisecond Pulsar Emission. I. Spectra, Pulse Shapes, and the Beaming Fraction

Abstract

We have monitored a large sample of millisecond pulsars using the 100-m Effelsberg radio telescope in order to compare their radio emission properties to the slowly rotating population. With some notable exceptions, our findings suggest that the two groups of objects share many common properties. A comparison of the spectral indices between samples of normal and millisecond pulsars demonstrates that millisecond pulsar spectra are not significantly different from those of normal pulsars. There is evidence, however, that millisecond pulsars are slightly less luminous and less efficient radio emitters compared to normal pulsars. We confirm recent suggestions that a diversity exists among the luminosities of millisecond pulsars with the isolated millisecond pulsars being less luminous than the binary millisecond pulsars. There are indications that old millisecond pulsars exhibit somewhat flatter spectra than the presumably younger ones. We present evidence that millisecond pulsar profiles are only marginally more complex than those found among the normal pulsar population. Moreover, the development of the profiles with frequency is rather slow, suggesting very compact magnetospheres. The profile development seems to anti-correlate with the companion mass and the spin period, again suggesting that the amount of mass transfer in a binary system might directly influence the emission properties. The angular radius of radio beams of millisecond pulsars does not follow the scaling predicted from a canonical pulsar model which is applicable for normal pulsars. Instead they are systematically smaller. The smaller inferred luminosity and narrower emission beams will need to be considered in future calculations of the birth-rate of the Galactic population.