X-ray bursts from the Terzan 5 transient IGR J17480-2446: nuclear rather than gravitational

TL;DR

This study analyzes the 2010 X-ray bursts from IGR J17480-2446, providing evidence that they are thermonuclear rather than gravitational in origin, challenging previous claims and supporting nuclear-burning models.

Contribution

The paper demonstrates that the bursts from IGR J17480-2446 are nuclear in origin, contrasting with prior suggestions of gravitational energy powering the bursts.

Findings

Burst-to-fluence ratio (~50-90) supports nuclear origin.

Burst properties differ from known type-II bursts.

Results confirm mHz QPOs are nuclear-powered.

Abstract

The 2010 outburst of the transient neutron star low-mass X-ray binary IGR J17480-2446 has exhibited a series of unique X-ray bursts, as well as millihertz (mHz) quasi-periodic oscillations (QPOs) related to these bursts. It has been recently proposed that these are type-II bursts, powered by the gravitational energy. This implies that the current nuclear-burning based model of mHz QPOs is not correct, and this timing feature cannot be used as a tool to measure the neutron star parameters. We report the analysis of the Rossi X-ray Timing Explorer data of IGR J17480-2446 to show that the burst properties of this source are quite different from the properties of the type-II bursts observed from the rapid burster and GRO J1744-28. For example, the inferred ratio (~ 50-90) of the non-burst fluence to burst fluence is consistent with the thermonuclear origin of IGR J17480-2446 bursts, and is significantly different from this ratio (< 4) for type-II bursts. Our results suggest that the bursts and the mHz QPOs from IGR J17480-2446 are powered by the nuclear energy.