Observations of pulsars at 9 millimetres

Abstract

Aims. The behaviour of the pulsar spectrum at high radio frequencies can provide decisive information about the nature of the radio emission mechanism. Methods. We report recent observations of a selected sample of pulsars at λ = 9 mm (32 GHz) with the 100-m Effelsberg radio telescope. Results. Three pulsars, PSR B0144+59, PSR B0823+26, and PSR B2022+50, were detected for the first time at this frequency. We confirm the earlier flux density measurements for a sample of six pulsars, and we are able to place upper flux density limits for another 12 pulsars. We find that all pulsar spectra have a simple form that can be described using only three parameters, one of which is the lifetime of short nano-pulses in the emission region. The study of the transition region from coherent to incoherent emission needs further and more sensitive observations at even higher radio frequencies.

Flux-density spectral analysis for several pulsars and two newly identified gigahertz-peaked spectra pulsars

“…(4) provided the best fit with a nano-shot timescale of about 30 ps which is only 10% of what was found for typical pulsars by Löhmer et al (2008). Alternatives (3) and (5) gave slightly worse agreements with the data, but generally speaking one finds that these three functions match the data quite well within the measured frequency interval.…”

“…It seems to be obvious that we are dealing with a GPS-type spectrum. However, the object is a potential candidate for a pulsar with spectra described using the model presented in Löhmer et al (2008). Thus, we attempted to fit three different functions that had been proposed in the literature, where…”

“…from Löhmer et al (2008) are based on a nano-shot emission model. We also considered the empirical function presented in Eq.…”

Pulsars with gigahertz-peaked spectra

“…There is no correlation between the profile type and the pulsar spectrum (M00). However, Löhmer et al (2008) show that the spectrum of PSR B0144+59 has a "turn up" at 5 GHz to 10 GHz, which may be caused by its peculiar high-frequency profile evolution. Lorimer et al (1995, hereafter L95) show a positive spectral index for some pulsars between 400 MHz and 1600 MHz.…”

Current instabilities in the pulsar magnetosphere

“…and there are indications of regular patterns of narrow emission regions separated on scales of a few m in Crab high-frequency giant pulses (Jessner et al 2010). Loehmer et al (2008) have shown that the superposition of sub-nanosecond emissions can also provide an explanation for the observed form of pulsar spectra. Our described solutions are stationary, but highly sensitive to the value of 1−κ κ and we expect small variations of the current density to cause large fluctuations in the local radio emission.…”