Ephemeris, orbital decay, and masses of ten eclipsing high-mass X-ray binaries

Abstract

We update the ephemeris of the eclipsing high-mass X-ray binary (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 help of more than ten years of monitoring these sources with the All Sky Monitor onboard RXTE and with the Integral Soft Gamma-Ray Imager onboard INTEGRAL. 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 light curves folded on the best determined orbital parameters of the sources. These light curves reveal complex eclipse ingresses and egresses that are understood mostly as being caused by accretion wakes. Our results constitute a database to be used for population and evolutionary studies of HMXBs and for theoretical modeling of long-term accretion in wind-fed X-ray binaries.

A 78 Day X-Ray Period Detected From NGC 5907 Ulx1 by Swift

“…Orbital periods can be imprinted on the observed light curves from X-ray binaries through (at least partial) eclipses by the companion star, or through some Be/X-ray binary-like phenomenon, in which the binary orbit is eccentric and the accretion rate is enhanced around periastron. We note, however, that the FREDlike cycle profile observed here does not bear much similarity to the majority of the orbital profiles compiled by Falanga et al (2015) for eclipsing X-ray binaries. The light curve observed here also does not show a series of quiescence-outburstquiescence cycles, as traditionally seen from Be/X-ray binaries (Reig 2011), and also from ESO 243-49 HLX-1, so any analogy here is limited.…”

High-mass X-ray binaries in the Milky Way

“…It orbits an O6.5 II-III supergiant, located at 5-8 kpc (Day and Tennant, 1991;Krzeminski, 1974), in 2.1 days with a small eccentricity, if any (van der Meer et al, 2007;Falanga et al, 2015). Mass transfer probably occurs through a combination of wind and disk accretion (Petterson, 1978;Tsunemi et al, 1996;Tjemkes et al, 1986;Kohmura et al, 2001;Suchy et al, 2008).…”

Masses, Radii, and the Equation of State of Neutron Stars

“…From these observables, it is possible to solve for the fundamental parameters of the binary, which include the mass of the neutron star MNS, the mass, radius and rotational angular velocity of the companion, Mopt, Ropt, Ωopt, and the inclination angle of the binary i. These measurements are typically less precise than those obtained from radio pulsar timing, and several sources of systematic uncertainty in this technique have been discussed inÖzel et al (2012) and Falanga et al (2015). The ten neutron stars whose masses have been estimated in this way are listed in Table 3.…”

“…Some of the possibilities considered to date include the presence of hyperons (Ambartsumyan & Saakyan 1960;Glendenning & Moszkowski 1991;Schulze et al 1995), hybrid stars containing free quarks (Collins & Perry 1975), or color superconducting phases (Alford & Reddy 2003;Alford et al 2005b). Moreover, self-bound stars consisting of strange quark matter have also been proposed (Farhi & Jaffe 1984;Haensel, Zdunik & Schaefer 1986;Alcock, Farhi & Olinto 1986). These models are based on the assumption that strange quark matter is the ultimate ground state of matter (Witten 1984) and they predict stellar radii that grow with the stellar mass.…”