Binary population synthesis of the Galactic canonical pulsar population

TL;DR

This work uses binary population synthesis with COMPAS to model the Galactic canonical pulsar population across radio and gamma-ray bands, incorporating natal kicks, Galactic dynamics, and selection effects. It employs a four-dimensional gamma-ray luminosity framework (fundamental plane) plus beaming and sensitivity modelling, and it contrasts predictions with ATNF radio pulsars and Fermi-LAT gamma-ray pulsars. Among 40 birth-property models, PN1-B1-D4 provides the best overall match to both radio and gamma-ray distributions and counts, though a degeneracy with the assumed star-formation rate remains a factor. The study also interrogates low-$\dot{E}$ gamma-ray emission via stacking, finding isotropic-like emission scenarios potentially favored, and highlights the vital role of selection effects and magnetic-field evolution in reconciling simulated populations with observations. These results lay groundwork for future work including MSPs, accretion-induced collapse channels, and richer magnetic field evolution modelling to interpret the Galactic gamma-ray background and related populations.

Abstract

Pulsars are rapidly rotating neutron stars that emit radiation across the electromagnetic spectrum, from radio to gamma-rays. We use the rapid binary population synthesis suite COMPAS to model the Galactic population of canonical pulsars. We account for both radio and gamma-ray selection effects, as well as the motion of pulsars in the Galactic potential due to natal kicks. We compare our models to the catalogues of pulsars detected in the radio, and those detected in gamma-rays by Fermi, and find broad agreement with both populations. We reproduce the observed ratio of radio-loud to radio-quiet gamma-ray pulsars. We further examine the possibility of low spin-down luminosity (Edot) pulsars emitting weak, unpulsed gamma-ray emission and attempt to match this with results from a recent gamma-ray stacking survey of these pulsars. We confirm the correlation between the latitude of a pulsar and its Edot arises due to natal kicks imparted to pulsars at birth, assuming that all pulsars are born in the Galactic disk.

Figures (12)

• Figure 1: CDFs of physical quantities for radio pulsars produced by the COMPAS models described in Table \ref{['tab:compas_parameter']} (coloured), compared to the data from the catalogues (black). CDFs from a given model are drawn from a randomised sampling from 10 realisations. From top left to bottom right, the panels show the distributions of $\dot{E}$ , radio flux, period, $\dot{P}$, Galactic latitude, and Galactic longitude.
• Figure 2: CDFs of physical quantities for $\gamma$-ray pulsars produced by the COMPAS models described in Table \ref{['tab:compas_parameter']} (coloured), compared to the data from the catalogues (black). CDFs from a given model are drawn from a randomised sampling from 10 realisations. From top left to bottom right, the panels show the distributions of $\dot{E}$ , radio flux, period, $\dot{P}$, Galactic latitude (b), and Galactic longitude (l).
• Figure 3: CDFs of various physical quantities predicted/produced by the PN1-B1-D4 model (red), compared to the data from the catalogues (blue). The red lines in these plots are from all ten realisations of the PN1-B1-D4 model that are sampled randomly as described in § \ref{['subsec:reusing_COMPAS']}. From top left to bottom right, the panels show the distributions of $\gamma$-ray pulsar $\dot{E}$ , radio pulsar $\dot{E}$ , $\gamma$-ray flux, radio flux, $\gamma$-ray pulsar period, radio pulsar period, $\gamma$-ray pulsar $\dot{P}$, radio pulsar $\dot{P}$, $\gamma$-ray pulsar galactic latitude, radio pulsar galactic latitude, $\gamma$-ray pulsar galactic longitude and radio pulsar galactic longitude. The p-values for each individual parameter as listed in Tables \ref{['tab:pvalues-radio']} & \ref{['tab:pvalues_gamma']} for one random realisation are plotted on each respective panel.
• Figure 4: Top: P-$\dot{P}$ diagram of Fermi detected canonical pulsars (blue) and detected $\gamma$-ray pulsars from the characteristic PN1-B1-D4 model (red); bottom: P-$\dot{P}$ diagram of radio detected canonical pulsars as recorded in the ATNF catalogue (blue) and detected radio pulsars from the characteristic PN1-B1-D4 model (red). The two black dashed lines represent the death-lines described in Eqs. \ref{['eq:dl1']} & \ref{['eq:dl2']}. The gray dashed lines labelled $10^3$ yr, $10^6$ yr, and $10^9$ yr represent constant characteristic age each respectively; and those labelled with $10^{31}$ erg s$^{-1}$ , $10^{33}$ erg s$^{-1}$ , and $10^{37}$ erg s$^{-1}$ represent constant $\dot{E}$ each respectively.
• Figure 5: Galactocentric coordinates of radio pulsars from the catalogue (blue) and from PN1-B1-D4 model (red). The yellow star in all panels except for the Y-Z planes indicates the location of the Sun.