Chandra and XMM-Newton observations of the low-luminosity X-ray pulsators SAX J1324.4-6200 and SAX J1452.8-5949

TL;DR

This study uses Chandra and XMM-Newton observations to analyze two low-luminosity X-ray pulsators, revealing their spectral properties, pulsation behavior, and potential classifications as neutron star binaries or other systems.

Contribution

First detailed X-ray and near-infrared analysis of SAX J1324.4-6200 and SAX J1452.8-5949, identifying their spectral characteristics, pulsation periods, and possible system types.

Findings

SAX J1324.4-6200 shows coherent pulsations at 172.86 s with increasing spin period.

Spectra of both sources fit well with power-law or black-body models.

SAX J1452.8-5949 likely not a high mass X-ray binary, possibly a main sequence star system.

Abstract

We present results from our Chandra and XMM-Newton observations of two low-luminosity X-ray pulsators SAX J1324.4-6200 and SAX J1452.8-5949 which have spin-periods of 172 s and 437 s respectively. The XMM-Newton spectra for both sources can be fitted well with a simple power-law model of photon index ~ 1.0. A black-body model can equally well fit the spectra with a temperature of ~ 2 keV for both sources. During our XMM-Newton observations, SAX J1324.4-6200 is detected with coherent X-ray pulsations at a period of $172.86 \pm 0.02$ s while no pulsations with a pulse fraction greater than 15% (at 98% confidence level) are detected in SAX J1452.8--5949. The spin period of SAX J1324.4-6200 is found to be increasing on a time-scale of $\dot{P}$ = $(6.34 \pm 0.08) \times 10^{-9}$ s s$^{-1}$ which would suggest that the accretor is a neutron star and not a white dwarf. Using sub-arcsec spatial resolution of the Chandra telescope, possible counterparts are seen for both sources in the near-infrared images obtained with the SOFI instrument on the New Technology Telescope. The X-ray and near-infrared properties of SAX J1324.4-6200 suggest it to be either a persistent high mass accreting X-ray pulsar or a symbiotic X-ray binary pulsar at a distance $\le$ 9 kpc. We identify the infrared counterpart of SAX J1452.8--5949 to be a late-type main sequence star at a distance $\le$ 10 kpc, thus ruling out SAX J1452.8--5949 to be a high mass X-ray binary. However with the present X-ray and near-infrared observations, we cannot make any further conclusive conclusion about the nature of SAX J1452.8-5949.