Spectro-timing analysis of Be X-ray pulsar SMC X-2 during the 2022 outburst

TL;DR

This study presents broadband X-ray observations of the Be X-ray pulsar SMC X-2 during its 2022 outburst, revealing spectral features, phase-dependent variability, and indications of super-critical accretion.

Contribution

First detailed broadband spectral and timing analysis of SMC X-2 during an outburst, including detection of cyclotron line and phase-resolved spectral variability.

Findings

Detection of cyclotron resonant scattering feature at 31 keV.

Spectral parameters vary significantly with pulse phase.

Evidence suggests the source is in a super-critical accretion regime.

Abstract

We present broadband X-ray observations of the High Mass X-ray Binary (HMXB) pulsar SMC X-2, using concurrent NuSTAR and NICER observations during its 2022 outburst. The source is found to be spinning with a period of 2.37281(3) s. We confirm the existence of cyclotron resonant scattering feature (CRSF) at 31 keV in addition to the iron emission line in the X-ray continuum of the source. Spectral analysis performed with the physical bulk and thermal Comptonization model indicates that the bulk Comptonization dominates the thermal Comptonization. Using phase-resolved spectroscopy, we have investigated the variations of the spectral parameters relative to pulse phase that may be due to the complex structure of magnetic field of the pulsar or the impact of the emission geometry. It is observed that the spectral parameters exhibit significant variabilities relative to the pulsed phase. Time-resolved spectroscopy is employed to examine the evolution of the continuum and changes in the spectral characteristics. Measurements of luminosity along with variations in cyclotron line energy and photon index suggest that the source may be accreting in the super-critical regime.