Repeating Ultraluminous X-ray Bursts and Repeating Fast Radio Bursts: A Possible Association?

TL;DR

This paper proposes a neutron star-white dwarf binary model to explain repeating ultraluminous X-ray bursts in NGC 5128 and explores a potential association with repeating fast radio bursts in extragalactic globular clusters.

Contribution

It introduces a novel binary model for ULXBs and suggests a possible link between repeating ULXBs and FRBs in globular clusters.

Findings

A neutron star-white dwarf binary can produce repeating ULXBs.

Repeating ULXBs and FRBs may be physically associated.

Follow-up observations are needed to confirm the association.

Abstract

Ultraluminous X-ray bursts (hereafter ULXBs) are ultraluminous X-ray flares with a fast rise ($\sim$ one minute) and a slow decay ($\sim$ an hour), which are commonly observed in extragalactic globular clusters. Most ULXBs are observational one-off bursts, whereas five flares from the same source in NGC 5128 were discovered by Irwin et al. (2016). In this Letter, we propose a neutron star (NS)-white dwarf (WD) binary model with super-Eddington accretion rates to explain the repeating behavior of the ULXB source in NGC 5128. With an eccentric orbit, the mass transfer occurs at the periastron where the WD fills its Roche lobe. The ultraluminous X-ray flares can be produced by the accretion column around the NS magnetic poles. On the other hand, some repeating fast radio bursts (hereafter FRBs) were also found in extragalactic globular clusters. Repeating ULXBs and repeating FRBs are the most violent bursts in the X-ray and radio bands, respectively. We propose a possible association between the repeating ULXBs and the repeating FRBs. Such an association is worth further investigation by follow-up observations on nearby extragalactic globular clusters.