Spectral analysis of SMC X-2 during its 2015 outburst

TL;DR

This study presents a detailed timing and spectral analysis of SMC X-2 during its 2015 outburst, revealing high luminosity, pulse period, spectral components, and evidence of photoionized matter around the source.

Contribution

First detailed spectral and timing analysis of SMC X-2 during its 2015 outburst, including pulse period, spectral components, and emission line identification.

Findings

Pulse period of 2.372267(5) seconds.

Detection of a soft thermal component at 0.15 keV.

Presence of emission lines indicating photoionized matter.

Abstract

We report on the results of Swift and XMM-Newton observations of SMC X-2 during its last outburst in 2015 October, the first one since 2000. The source reached a very high luminosity ($L \sim 10^{38}$ erg s$^{-1}$), which allowed us to perform a detailed analysis of its timing and spectral properties. We obtained a pulse period $P_{\rm spin}$ = 2.372267(5) s and a characterization of the pulse profile also at low energies. The main spectral component is a hard ($\Gamma \simeq 0$) power-law model with an exponential cut-off, but at low energies we detected also a soft (with kT $\simeq$ 0.15 keV) thermal component. Several emission lines can be observed at various energies. The identification of these features with the transition lines of highly ionized N, O, Ne, Si, and Fe suggests the presence of photoionized matter around the accreting source.