Relativistically broadened iron line in the SUZAKU observation of the neutron star X-ray binary 4U 1705-44

TL;DR

This study analyzes Suzaku X-ray observations of the neutron star binary 4U 1705-44, revealing a relativistically broadened iron line that provides insights into the inner accretion disk structure and ionization variability.

Contribution

First detection of a relativistically broadened iron line in 4U 1705-44 using Suzaku, with detailed modeling of disk radius and ionization changes over multiple observations.

Findings

Inner disk radius at ~10.5 GM/c^2

Disk inclination angle ~30 degrees

Ionization level varies by two orders of magnitude

Abstract

The X-ray spectra of accreting compact objects often exhibit discrete emission features associated with fluorescent emission in the accretion disk, the strongest of which is the Fe Kalpha fluorescence line at 6.4--6.97keV. These reflection features are amongst the best tools in the study of the inner region of accretion flow around a compact object. Here we report on three Suzaku observations of the neutron star X-ray binary 4U1705-44 where a broad, skewed Fe Kalpha emission line is clearly visible above the continuum. By using a relativistically-blurred reflection model we find that in 4U1705-44 the inner disk radius extends down to rin=10.5^{+1.0}_{-1.7} GM/c^2 and is at an angle of 29.8^{+1.1}_{-1.0} degrees to the line of sight. Furthermore, we find that the level of ionisation in the surface layers of the accretion disk changes by two orders of magnitude between the three observations, however the inner radius obtained from the line profile remains stable.