Losing a minute every two years: SRG X-ray view of the rapidly accelerating X-ray pulsar SXP 1323

¹ Space Research Institute, Russian Academy of Sciences, Profsoyuznaya 84/32, 117997 Moscow, Russia
e-mail: i.a.mereminskiy@gmail.com
² Leiden Observatory, Leiden University, 2300RA Leiden, The Netherland
³ Department of Physics and Astronomy, 20014 University of Turku, Finland

Received: 16 July 2021
Accepted: 24 November 2021

Abstract

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