The ephemeris, orbital decay, and masses of 10 eclipsing HMXBs

TL;DR

This study analyzes over a decade of data from multiple X-ray observatories to refine orbital parameters, masses, and eclipse behaviors of ten eclipsing high-mass X-ray binary systems, providing valuable data for future astrophysical research.

Contribution

It offers the first accurate measurements of apsidal advance and updated neutron star masses in ten HMXBs, enhancing understanding of their orbital evolution and accretion processes.

Findings

Refined orbital period decay measurements.

First accurate apsidal advance values for Vela X-1 and 4U 1538-522.

Complex eclipse ingress and egress patterns linked to accretion wakes.

Abstract

We take advantage of more than 10 years of monitoring of the eclipsing HMXB systems LMC X-4, Cen X-3, 4U 1700-377, 4U 1538-522, SMC X-1, IGR J18027-2016, Vela X-1, IGR J17252-3616, XTE J1855-026, and OAO 1657-415 with the ASM on-board RXTE and ISGRI on-board INTEGRAL to update their ephemeris. These results are used to refine previous measurements of the orbital period decay of all sources (where available) and provide the first accurate values of the apsidal advance in Vela X-1 and 4U 1538-522. Updated values for the masses of the neutron stars hosted in the ten HMXBs are also provided, as well as the long-term lightcurves folded on the sources best determined orbital parameters. These lightcurves reveal complex eclipse ingresses and egresses, that are understood mostly as being due to the presence of accretion wakes. The results reported in this paper constitute a database to be used for population and evolutionary studies of HMXBs, as well as theoretical modelling of long-term accretion in wind-fed X-ray binaries.