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

Pushchino Radio Astronomy Observatory, Astro Space Center, Lebedev Physical Institute, Pushchino, Moscow Region, 142290, Russia

Corresponding author: A. Kuzmin, akuzmin@prao.psn.ru

Received: 28 July 2000
Accepted: 22 December 2000

Abstract

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.