Chandra Observation of Quiescent Low-Mass X-ray Binaries in the Globular Cluster NGC 6304

TL;DR

This study analyzes quiescent low-mass X-ray binaries in NGC 6304 using Chandra, confirming spectral characteristics and flux variations consistent with deep crustal heating models, and resolving one source into two components.

Contribution

First detailed Chandra analysis of qLMXBs in NGC 6304, resolving a core source into two components and comparing spectral and flux properties with previous observations.

Findings

XMMU 171433-292747 is resolved into two sources with distinct spectra.

Spectral parameters are consistent with deep crustal heating models.

Flux of XMMU 171421-292917 decreased by about half.

Abstract

This paper presents the analysis of candidate quiescent low mass xray binarie (qLMXBs) observed during a short Chandra/ACIS observation of the globular cluster (GC) NGC 6304. Two out of the three candidate qLMXBs of this cluster, XMMU 171433-292747 and XMMU 171421-292917, lie within the field of view. This permits comparison with the discovery observation of these sources. The one in the GC core -- XMMU 171433-292747 -- is spatially resolved into two separate X-ray sources, one of which is consistent with a pure H-atmosphere qLMXB, and the other is an X-ray power-law spectrum source. These two spectral components separately account for those observed from XMMU 171433-292747 in its discovery observation. We find that the observed flux and spectral parameters of the H-atmosphere spectral components are consistent with the previous observation, as expected from a qLMXB powered by deep crustal heating. XMMU 171421-292917 also has neutron star atmosphere spectral parameters consistent with those in the XMM-Newton observation and the observed flux has decreased by a factor 0.54^{+0.30}_{-0.24}.