Swift reveals the eclipsing nature of the high mass X-ray binary IGR~J16195-4945

TL;DR

This study confirms the eclipsing nature of the high mass X-ray binary IGR J16195-4945 using Swift data, revealing its orbital period, eclipse duration, and spectral characteristics, thus enhancing understanding of its binary system properties.

Contribution

First detection of the orbital period and eclipse in IGR J16195-4945 through Swift observations, providing detailed timing and spectral analysis of this high mass X-ray binary.

Findings

Orbital period of 3.945 days identified with high significance.

Eclipse lasting approximately 3.5% of the orbital period.

Spectrum characterized by a strongly absorbed flat power law with cutoff at 14 keV.

Abstract

IGR J16195-4945 is a hard X-ray source discovered by INTEGRAL during the Core Program observations performed in 2003. We analyzed the X-ray emission of this source exploiting the Swift-BAT survey data from December 2004 to March 2015, and all the available Swift-XRT pointed observations. The source is detected at a high significance level in the 123-month BAT survey data, with an average 15-150 keV flux of the source of ~1.6 mCrab. The timing analysis on the BAT data reveals with a significance higher than 6 standard deviations the presence of a modulated signal with a period of 3.945 d, that we interpret as the orbital period of the binary system. The folded light curve shows a flat profile with a narrow full eclipse lasting ~3.5% of the orbital period. We requested phase-constrained XRT observations to obtain a more detailed characterization of the eclipse in the soft X-ray range. Adopting resonable guess values for the mass and radius of the companion star, we derive a semi-major orbital axis of ~31 R_sun, equivalent to ~1.8 times the radius of the companion star. From these estimates and from the duration of the eclipse we derive an orbital inclination between 55 and 60 degrees. The broad band time-averaged XRT+BAT spectrum is well modeled with a strongly absorbed flat power law, with absorbing column N_H=7x 10^22 cm^(-2) and photon index Gamma=0.5, modified by a high energy exponential cutoff at E_cut=14 keV.