The peculiar Galactic center neutron star X-ray binary XMM J174457-2850.3

TL;DR

This paper studies the Galactic center neutron star X-ray binary XMM J174457-2850.3, revealing its unique X-ray variability, spectrum, and thermonuclear burst, which suggest it is an accreting neutron star with transitional behavior between outburst and quiescence.

Contribution

It demonstrates that XMM J174457-2850.3 exhibits properties similar to transitional neutron star systems, providing insights into accretion and magnetic interactions in such objects.

Findings

Detection of a thermonuclear burst confirming neutron star nature.

Observation of variable X-ray luminosity during outbursts and quiescence.

Hard X-ray spectrum with a power-law index of ~1.4 indicating magnetic accretion interactions.

Abstract

The recent discovery of a milli-second radio pulsar experiencing an accretion outburst similar to those seen in low mass X-ray binaries, has opened up a new opportunity to investigate the evolutionary link between these two different neutron star manifestations. The remarkable X-ray variability and hard X-ray spectrum of this object can potentially serve as a template to search for other X-ray binary/radio pulsar transitional objects. Here we demonstrate that the transient X-ray source XMM J174457-2850.3 near the Galactic center displays similar X-ray properties. We report on the detection of an energetic thermonuclear burst with an estimated duration of ~2 hr and a radiated energy output of ~5E40 erg, which unambiguously demonstrates that the source harbors an accreting neutron star. It has a quiescent X-ray luminosity of Lx~5E32 erg/s and exhibits occasional accretion outbursts during which it brightens to Lx~1E35-1E36 erg/s for a few weeks (2-10 keV). However, the source often lingers in between outburst and quiescence at Lx~1E33-1E34 erg/s. This unusual X-ray flux behavior and its relatively hard X-ray spectrum, a power law with an index of ~1.4, could possibly be explained in terms of the interaction between the accretion flow and the magnetic field of the neutron star.