The evolution of inner disk radius with orbital phase in Circinus X-1

TL;DR

This study analyzes RXTE data to observe how the inner disk radius of Cir X-1 varies with orbital phase, revealing orbital modulation likely caused by high eccentricity and detailing the relationship between disk luminosity and temperature.

Contribution

It provides the first detailed analysis of the orbital modulation of the inner disk radius in Cir X-1 using RXTE observations, highlighting the impact of orbital eccentricity.

Findings

Inner disk radius shows clear orbital modulation.

Disk luminosity inversely correlates with inner disk temperature.

Rapid decrease of R_in occurs as neutron star departs from companion.

Abstract

Using RXTE observations, we investigate the evolution of inner disk radius R_in of Cir X-1 during two cycles and find obvious orbital modulation. We argue that the modulation is attributed to its high orbital eccentricity. The disk luminosity is inversely with the inner disk temperature kT_in, which is ascribed to the slow increase of kT_in and, however, the rapid decrease of R_in during the passage for the neutron star to depart from the companion star.