PSR J1755$-$2550: A young radio pulsar with a massive, compact companion

TL;DR

This paper reports on the discovery and analysis of PSR J1755-2550, a young, non-recycled radio pulsar in a binary system, with uncertain companion type, and discusses its implications for binary evolution and supernovae.

Contribution

It provides detailed timing analysis of PSR J1755-2550 and explores the nature of its companion using population synthesis and observational searches, highlighting its rarity.

Findings

PSR J1755-2550 is a young, non-recycled pulsar with a 315 ms spin period.

The companion is likely either a massive white dwarf or a neutron star, with both options being equally probable.

Population synthesis predicts a minimum companion mass of 0.90 M_sun and potential for merging systems that could produce Ca-rich supernovae.

Abstract

Radio pulsars found in binary systems with short orbital periods are usually fast spinning as a consequence of recycling via mass transfer from their companion stars; this process is also thought to decrease the magnetic field of the neutron star being recycled. Here, we report on timing observations of the recently discovered binary PSR J1755$-$2550 and find that this pulsar is an exception: with a characteristic age of 2.1 Myr, it is relatively young; furthermore, with a spin period of 315 ms and a surface magnetic field strength at its poles of 0.88$\times$10$^{12}$ G the pulsar shows no sign of having been recycled. Based on its timing and orbital characteristics, the pulsar either has a massive white dwarf (WD) or a neutron star (NS) companion. To distinguish between these two cases, we searched radio observations for a potential recycled pulsar companion and analysed archival optical data for a potential WD companion. Neither work returned conclusive detections. We apply population synthesis modelling and find that both solutions are roughly equally probable. Our population synthesis also predicts a minimum mass of 0.90 M$_{\odot}$ for the companion star to PSR J1755$-$2550 and we simulate the systemic runaway velocities for the resulting WDNS systems which may merge and possibly produce Ca-rich supernovae. Whether PSR J1755$-$2550 hosts a WD or a NS companion star, it is certainly a member of a rare subpopulation of binary radio pulsars.