The variable radio jet of the accreting neutron star the Rapid Burster

TL;DR

This study investigates the radio jet variability of the Rapid Burster during prolific X-ray bursting, finding significant radio flux changes and exploring a tentative link between Type-II bursts and jet behavior, with implications for jet models.

Contribution

It provides the first simultaneous radio and X-ray observations of the Rapid Burster, analyzing jet variability during intense Type-II bursting and proposing potential burst-jet interactions.

Findings

Radio flux varies significantly during observations.

No definitive causal link established between bursts and jet changes.

Possible tentative connection suggesting bursts may influence jet strength.

Abstract

The Rapid Burster is a unique neutron star low-mass X-ray binary system, showing both thermonuclear Type-I and accretion-driven Type-II X-ray bursts. Recent studies have demonstrated how coordinated observations of X-ray and radio variability can constrain jet properties of accreting neutron stars - particularly when the X-ray variability is dominated by discrete changes. We present a simultaneous VLA, Swift, and INTEGRAL observing campaign of the Rapid Burster to investigate whether its jet responds to Type-II bursts. We observe the radio counterpart of the X-ray binary at its faintest-detected radio luminosity, while the X-ray observations reveal prolific, fast X-ray bursting. A time-resolved analysis reveals that the radio counterpart varies significantly between observing scans, displaying a fractional variability of $38 \pm 5$%. The radio faintness of the system prevents the robust identification of a causal relation between individual Type-II bursts and the evolution of the radio jet. However, based on a comparison of its low radio luminosity with archival Rapid Burster observations and other accreting neutron stars, and on a qualitative assessment of the X-ray and radio light curves, we explore the presence of a tentative connection between bursts and jet: i.e., the Type-II bursts may weaken or strengthen the jet. The former of those two scenarios would fit with magneto-rotational jet models; we discuss three lines of future research to establish this potential relation between Type-II bursts and jets more confidently.