X-ray Spectroscopy of the High Mass X-ray Binary Pulsar Centaurus X-3 over its Binary Orbit

TL;DR

This study analyzes the X-ray spectral behavior of the pulsar Centaurus X-3 over its orbit, revealing rare dips caused by dense matter obscuration, with detailed spectral modeling during different orbital phases.

Contribution

It provides the first detailed spectral analysis of Cen X-3 during dips and eclipse, highlighting the role of dense matter in causing obscuration and spectral changes.

Findings

Dips observed up to ~40 keV with high absorption.

Iron line intensities decrease by a factor of 2-3 during dips.

Spectral changes suggest obscuration by dense matter in the accretion disk.

Abstract

We present a comprehensive spectral analysis of the high mass X-ray binary (HMXB) pulsar Centaurus X-3 with the Suzaku observatory covering nearly one orbital period. The light curve shows the presence of extended dips which are rarely seen in HMXBs. These dips are seen up to as high as ~40 keV. The pulsar spectra during the eclipse, out-of-eclipse, and dips are found to be well described by a partial covering power-law model with high energy cut-off and three Gaussian functions for 6.4 keV, 6.7 keV, and 6.97 keV iron emission lines. The dips in the light curve can be explained by the presence of an additional absorption component with high column density and covering fraction, the values of which are not significant during the rest of the orbital phases. The iron line parameters during the dips and eclipse are significantly different compared to those during the rest of the observation. During the dips, the iron line intensities are found to be lesser by a factor of 2--3 with significant increase in the line equivalent widths. However, the continuum flux at the corresponding orbital phase is estimated to be lesser by more than an order of magnitude. Similarities in the changes in the iron line flux and equivalent widths during the dips and eclipse segments suggests the dipping activity in Cen X-3 is caused by obscuration of the neutron star by dense matter, probably structures in the outer region of the accretion disk, as in case of dipping low mass X-ray binaries.