PSR J1618−3921: a recycled pulsar in an eccentric orbit

F Octau,P C C Freire,G Theureau,G Desvignes,T M Tauris,L Guillemot,I Cognard

doi:10.1051/0004-6361/201731928

Abstract

Context.The 11.99 ms pulsar PSR J1618−3921 orbits a He white dwarf companion of probably low mass with a period of 22.7 d. The pulsar was discovered in a survey of the intermediate Galactic latitudes at 1400 MHz that was conducted with the Parkes radio telescope in the late 1990s. Although PSR J1618−3921 was discovered more than 15 years ago, only limited information has been published about this pulsar, which has a surprisingly high orbital eccentricity (e≃ 0.027) considering its high spin frequency and the likely low mass of the companion.Aims.The focus of this work is a precise measurement of the spin and the astrometric and orbital characteristics of PSR J1618−3921. This was done with timing observations made at the Nançay Radio Telescope from 2009 to 2017.Methods.We analyzed the timing data recorded at the Nançay Radio Telescope over several years to characterize the properties of PSR J1618−3921. A rotation ephemeris for this pulsar was obtained by analyzing the arrival times of the radio pulses at the telescope.Results.We confirm the unusual eccentricity of PSR J1618−3921 and discuss several hypotheses regarding its formation in the context of other discoveries of recycled pulsars in eccentric orbits.

Highlights

The pulsar PSR J1618−3921 is a Galactic-disk recycled pulsar discovered in a 1.4-GHz survey of the intermediate Galactic latitudes with the Parkes radio telescope (Edwards & Bailes 2001)
PSR J1618−3921 was discovered more than 15 years ago, only limited information has been published about this pulsar, which has a surprisingly high orbital eccentricity (e 0.027) considering its high spin frequency and the likely low mass of the companion
We confirm the unusual eccentricity of PSR J1618−3921 and discuss several hypotheses regarding its formation in the context of other discoveries of recycled pulsars in eccentric orbits

Summary

Introduction

The pulsar PSR J1618−3921 is a Galactic-disk recycled pulsar discovered in a 1.4-GHz survey of the intermediate Galactic latitudes with the Parkes radio telescope (Edwards & Bailes 2001). In the “standard” pulsar recycling scenario, millisecond pulsars (MSPs, here defined as pulsars with spin periods shorter than 15 ms) are spun-up by mass and angular momentum transfer from a companion star in a low-mass X-ray binary (Alpar et al 1982; Radhakrishnan & Srinivasan 1982; Bhattacharya & van den Heuvel 1991; Tauris & van den Heuvel 2006) This process leads to highly circularized orbits, that is, orbits with very low eccentricities, e (Phinney & Kulkarni 1994). PSR J1618−3921 and the other MSPs in this growing pulsar class display very similar orbital periods and eccentricity values (see Table 1), which suggests a common, non-chaotic formation process (Freire & Tauris 2014; Antoniadis 2014; Jiang et al 2015).

Observations and data analysis

Discussion

Conclusion and future work