The Galactic population and properties of young, highly energetic pulsars

Abstract

The population of young, non-recycled pulsars with spin down energies $\dot{E} >10^{35}$ erg s−1 is sampled predominantly at γ-ray and radio wavelengths. A total of 137 such pulsars are known, with partial overlap between the sources detectable in radio and γ-rays. We use a very small set of assumptions in an attempt to test whether the observed pulsar sample can be explained by a single underlying population of neutron stars. For radio emission we assume a canonical conal beam with a fixed emission height of 300 km across all spin periods and a luminosity law which depends on $\dot{E}^{0.25}$. For γ-ray emission we assume the outer-gap model and a luminosity law which depends on $\dot{E}^{0.5}$. We synthesise a population of fast-spinning pulsars with a birth rate of one per 100 years. We find that this simple model can reproduce most characteristics of the observed population with two caveats. The first is a deficit of γ-ray pulsars at the highest $\dot{E}$ which we surmise to be an observational selection effect due to the difficulties of finding γ-ray pulsars in the presence of glitches without prior knowledge from radio frequencies. The second is a deficit of radio pulsars with interpulse emission, which may be related to radio emission physics. We discuss the implications of these findings.

Constraining the origin of the puzzling source HESS J1640-465 and the PeVatron candidate HESS J1641-463 using Fermi-LAT observations

“…collaboration, together with our hard spectral index of 1.8 strongly disfavour the pulsar hypothesis for HESS J1640−465. The fact that no γ-ray pulsations have been detected coming from an Xray pulsar with such a high Ė (4.4 × 10 36 erg s −1 ) could be explained as in Johnston et al (2020). These X-ray pulsars have a selection bias making them at great distance, deep in the Galactic plane, and thus below LAT sensitivity.…”

The Thousand-Pulsar-Array programme on MeerKAT IV: Polarisation properties of young, energetic pulsars

“…Rookyard et al (2017) showed that it is possible to distinguish between pulsars which are seen in radio but not γ-rays and those which are visible at both wavebands based on the width of the radio profile (W). In addition, the modelling in Johnston et al (2020a) showed that γ-ray pulsars are not expected above a line which follows:…”

“…A pulsar's geometry can be characterised by two angles, α the inclination angle of the magnetic axis to the rotation axis and β the angle between the observer's line-of-sight and the magnetic axis. Johnston et al (2020a) demonstrated that (statistically speaking) joint radio and γ-ray pulsars have high values of α (i.e. were close to orthogonal) and low values of β whereas radio-only pulsars tended to have lower values of α.…”

“…In a recent paper, Johnston et al (2020a) examined the population of young, energetic pulsars with spin-down energy loss rates, E, above 10 35 erg s −1 . They built a model of the underlying Galactic population of these objects and determined the ratios between pulsars seen in the radio, in γ-rays or both.…”

“…Those with radio counterparts are expected to have high values of α and/or narrow pulse widths and we will test this idea. Finally, we will examine pulsars with interpulses; these orthogonal rotators should be preferentially detected in γ-rays at lower E (Johnston et al 2020a).…”