Losing a minute every two years: SRG X-ray view on the rapidly accelerating X-ray pulsar SXP1323

TL;DR

This study presents the first broadband X-ray analysis of the peculiar pulsar SXP 1323, revealing its spectral properties, spin evolution, and consistent accretion characteristics over five years.

Contribution

It provides the first broadband 1-20 keV spectrum of SXP 1323 and traces its spin evolution, highlighting a linear spin-up phase since 2016.

Findings

Broadband spectrum typical for accreting X-ray pulsars

Spin period has been decreasing linearly since 2016

No spectral difference between pulsation and non-pulsation states

Abstract

SXP 1323 is a peculiar high-mass X-ray binary located in the Small Magellanic Cloud, renowned for its rapid spin-up. We investigate for the first time broadband X-ray properties of SXP1323, as observed by the Mikhail Pavlinsky ART-XC and eRosita telescopes on board the SRG observatory. Using ART-XC and eRosita, data we produced first broadband 1-20 keV X-ray spectrum and estimated pulsed fraction above 8 keV. With the addition of archival XMM-Newton observations we traced evolution of the SXP 1323 spin period over the last five years and found that after 2016 the source switched to a linear spin-up with rate of -29.9 s yr$^{-1}$. Broadband X-ray spectrum is typical for accreting X-ray pulsars, with steep powerlaw index ($\Gamma$=-0.15) and exponential cutoff energy of 5.1 keV. No significant difference between spectra obtained in states with and without pulsations were found.