The Galactic population of canonical pulsars

II. Taking into account several evolutionary paths: Interstellar medium interaction, Galactic potential, and a death valley

¹ Université de Strasbourg, CNRS, Observatoire Astronomique de Strasbourg, UMR 7550, 67000 Strasbourg, France
² National Centre for Radio Astrophysics, Tata Institute for Fundamental Research, Post Bag 3, Ganeshkhind, Pune 411007, India
³ Janusz Gil Institute of Astronomy, University of Zielona Góra, ul. Szafrana 2, 65-516 Zielona, Góra, Poland

^⋆ Corresponding author; matteo.sautron@astro.unistra.fr

Received: 13 June 2024
Accepted: 16 October 2024

Abstract

Context. Pulsars are highly magnetised rotating neutron stars, emitting in a broad electromagnetic energy range. These objects were discovered more than 55 years ago and are astrophysical laboratories for studying physics at extreme conditions. Reproducing the observed pulsar population helps refine our understanding of their formation and evolution scenarios, as well as their radiation processes and geometry.

Aims. In this paper, we improve our previous population synthesis by focusing on both the radio and γ-ray pulsar populations, investigating the impact of the Galactic gravitational potential and of the radio emission death line. To elucidate the necessity of a death line, we implemented our refined initial distributions of the spin period and spacial position at birth. This approach allowed us to elevate the sophistication of our simulations to the most recent state-of-the-art approaches.

Methods. The motion of each individual pulsar was tracked in the Galactic potential by a fourth-order symplectic integration scheme. Our pulsar population synthesis took into account the secular evolution of the force-free magnetosphere and magnetic field decay simultaneously and self-consistently. Each pulsar was evolved from birth to the present time. The radio and γ-ray emission locations were modelled by the polar cap geometry and striped wind model, respectively.

Results. By simulating ten million pulsars, we found that including a death line allows us to better reproduce the observational trend. However, when simulating one million pulsars, we obtained an even more realistic P−Ṗ diagram, whether or not a death line was included. This suggests that the ages of the detected pulsars might be overestimated and so, it sets the need for a death line in pulsar population studies into question. Kolmogorov-Smirnov tests confirm the statistical similarity between the observed and simulated P−Ṗ diagram. Additionally, simulations with increased γ-ray telescope sensitivities hint at a significant contribution coming from the γ-ray pulsars to the GeV excess in the Galactic centre.