A Deep Chandra X-ray Observatory Study of the Millisecond Pulsar Population in the Globular Cluster Terzan 5

TL;DR

This study analyzes extensive Chandra X-ray data to investigate the millisecond pulsar population in Terzan 5, revealing X-ray counterparts, variability, and insights into their emission mechanisms within a dense globular cluster.

Contribution

It provides the first detailed X-ray analysis of Terzan 5's MSPs, highlighting variability and detection challenges due to spectral and environmental factors.

Findings

8 MSPs have plausible X-ray matches

Detection limited by absorption and crowding

Evidence of orbital variability in redback and black widow MSPs

Abstract

We present an analysis of 745.6 ks of archival Chandra X-ray Observatory Advanced CCD Imaging Spectrometer data accumulated between 2000 and 2016 of the millisecond pulsar (MSP) population in the rich Galactic globular cluster Terzan 5. Eight of the 37 MSPs with precise positions are found to have plausible X-ray source matches. Despite the deep exposure, the remaining MSPs are either marginally detected or have no obvious X-ray counterparts, which can be attributed to the typically soft thermal spectra of rotation-powered MSPs, which are strongly attenuated by the high intervening absorbing column (~$10^{22}$ cm$^{-2}$) towards the cluster, and in some instances severe source crowding/blending. For the "redback" MSP binaries, PSRs J1748-2446P and J1748-2446ad, and the "black widow" binary PSRs J1748-2446O, we find clear evidence for large-amplitude X-ray variability at the orbital period consistent with an intrabinary shock origin. The third redback MSP in the cluster, PSR J1748-2446A, shows large amplitude variations in flux on time scales of years, possibility due to state transitions or intense flaring episodes from the secondary star.