Electron Cyclotron Maser Emission as the Driving Mechanism in Long-Period Radio Transients

TL;DR

This paper proposes that electron cyclotron maser emission (ECME) explains the polarization, narrow pulses, and luminosities of long-period radio transients, suggesting they originate from slowly rotating neutron stars with low magnetic fields accreting from the interstellar medium.

Contribution

It introduces ECME as the mechanism behind LPRTs and explains their polarization and pulse profiles, linking their properties to neutron star magnetospheres and accretion.

Findings

ECME can produce highly polarized, narrow pulses consistent with observations.

Detectability favors slowly rotating neutron stars with low magnetic fields.

Power levels are sufficient when considering strong beaming effects.

Abstract

Long-period radio transients (LPRTs) are highly polarised, coherent radio sources with periods of minutes to hours and bursts typically lasting 10 to 100 s. Here we consider the apparently isolated subclass of LPRTs and argue that electron cyclotron maser emission (ECME) explains their narrow duty cycles and polarisation properties. In particular, we show that intrinsically circular ECME can emerge as predominantly linear after undergoing Faraday conversion in an overlying magnetospheric plasma layer, thus reconciling the observed high linear fractions with a circularly polarised maser. In this picture, a rotating oblique magnetosphere beams radiation into a thin, hollow emission cone whose surface lies almost perpendicular to the local magnetic field. The observed very narrow pulses arise when the line of sight skims the cone, while broader profiles and weak leading or trailing components occur when multiple azimuths along the emission ring meet the maser resonance condition. The observed isotropic-equivalent luminosities of about 10^30 to 10^31 erg s^-1 correspond to modest intrinsic powers once strong ECME beaming is taken into account. We show that such power levels can be supplied by accretion from the interstellar medium (ISM), and that detectability at kiloparsec distances favours slowly rotating neutron stars with comparatively low surface magnetic fields below about 10^10 Gauss and low space velocities.