A Search for Pulsar Companions Around Low-Mass White Dwarfs

TL;DR

This study conducted a sensitive search for pulsars around low-mass white dwarfs using the Effelsberg Radio Telescope but found no signals, constraining the fraction of neutron star companions in such systems.

Contribution

First targeted search for pulsars around low-mass white dwarfs accounting for orbital motion, providing constraints on neutron star companion fractions.

Findings

No pulsar signals detected in the observed systems.

Upper limit of 10% for the fraction of neutron star companions.

Results combined with previous non-detections to refine constraints.

Abstract

We report on a search for pulsars at the positions of eight low-mass white dwarfs and one higher-mass white dwarf with the 100-m Effelsberg Radio Telescope. These systems have orbital parameters suggesting that their unseen companions are either massive white dwarfs or neutron stars. Our observations were performed at 1.36 GHz, reaching sensitivities of 0.1-0.2 mJy. We searched our data accounting for the possible acceleration and jerk of the pulsar signals due to orbital motion, but found no significant pulsar signals. Considering our result jointly with 20 non-detections of similar systems with the Greenbank Radio Telescope, we infer $f_{\rm NS}\leq 0.10$, for the fraction of NSs orbiting these white dwarfs. We discuss the sensitivity of this result to the underlying assumptions and conclude with a brief discussion on the prospects of targeted surveys for discovering millisecond pulsars.