Detection of X-ray Emission from a Bright Long-Period Radio Transient

TL;DR

This paper reports the discovery of a unique long-period radio transient with coincident X-ray emission, challenging existing models and suggesting a new class of hour-scale X-ray transients linked to bright radio signals.

Contribution

It presents the first detection of an LPT with simultaneous X-ray and radio emission, proposing new explanations involving magnetars or highly magnetized white dwarfs.

Findings

Detected a bright LPT with 44.2-minute period in radio and X-ray.

Found correlated variability between radio and X-ray luminosities.

Identified a new class of hour-scale X-ray transients associated with bright radio emission.

Abstract

Recently, a class of long-period radio transients (LPTs) has been discovered, exhibiting emission on timescales thousands of times longer than radio pulsars. Several models had been proposed implicating either a strong magnetic field neutron star, isolated white dwarf pulsar, or a white dwarf binary system with a low-mass companion. While several models for LPTs also predict X-ray emission, no LPTs have been detected in X-rays despite extensive searches. Here we report the discovery of an extremely bright LPT (10-20 Jy in radio), ASKAP J1832-0911, which has coincident radio and X-ray emission, both with a 44.2-minute period. The X-ray and radio luminosities are correlated and vary by several orders of magnitude. These properties are unique amongst known Galactic objects and require a new explanation. We consider a $\gtrsim0.5$ Myr old magnetar with a $\gtrsim 10^{13}$ G crustal field, or an extremely magnetised white dwarf in a binary system with a dwarf companion, to be plausible explanations for ASKAP J1832-0911, although both explanations pose significant challenges to formation and emission theories. The X-ray detection also establishes a new class of hour-scale periodic X-ray transients of luminosity $\sim10^{33}$ erg/s associated with exceptionally bright coherent radio emission.