High-resolution X-ray spectroscopy of Cen X-3 with XMM-Newton

TL;DR

This study analyzes high-resolution X-ray spectra of Cen X-3 from XMM-Newton, revealing heavily absorbed continuum, emission lines, and plasma conditions around the compact object during eclipse and out-of-eclipse phases.

Contribution

It provides detailed spectral analysis distinguishing eclipse and out-of-eclipse environments, highlighting the presence of a hybrid plasma and accretion stream instabilities.

Findings

Detection of emission lines from Si v, Mg xii, Mg xi, and Ne x.

He-like triplet analysis indicates high electron density (>10^12 cm^-3).

Dips in out-of-eclipse light curve are due to accretion stream instabilities.

Abstract

The spectral analysis of two XMM-Newton observations of the high-mass X-ray binary system Cen X-3 is presented. In particular, it is focused on the eclipse and out-of-eclipse spectra in order to compare the properties of the environment around the compact object. The high-resolution spectra obtained from the reflection grating spectrometer on board XMM-Newton was analysed focusing on studying eclipse and out-of-eclipse spectra separately. Several continuum models were explored in SPEX for which we studied the properties of emitting and absorbing matter depending on the emission and absorption lines identified in the spectra. It was found that the X-ray continuum is heavily absorbed by a neutral gas and photoionised matter. Emission lines from Si v, Mg xii, Mg xi, and Ne x were detected in the eclipse spectrum. In particular, H-like lines of Mg and Ne with a significance greater than 5 sigma in the eclipse spectrum and 3 sigma in the out-of-eclipse spectrum. But in the out-of-eclipse spectrum any absorption lines, if any, were detected with a significance less than 2 sigma. RGS light curve showed dips in the out-of-eclipse spectrum which are not due to an increase in the column absorption but may be produced by instabilities in the accretion stream. On the other hand, the level of counts above 20 was compatible with the X-ray background. A simple local continuum model was used to describe the He-like triplet of Ne and the derived values of R and G ratio parameters pointed out that the UV photospheric field should be important at the line production site and an electron density greater than 10(12) cm-3. As a consequence, a hybrid plasma may be present in the binary system.