The Orbit of the Massive X-Ray Binary LS 5039

Abstract

We present the first spectroscopic orbit for the massive X-ray binary LS 5039, which we find to be a shortperiod ( days) and highly eccentric ( ) system. The low-mass function for P p 4.117 ‫ע‬ 0.011 e p 0.41 ‫ע‬ 0.05 the orbit appears to be most consistent with a neutron star companion, although a black hole remains a possibility if the system has a low inclination. The spectrum of the O7 V optical star appears to be normal for its type (suggesting that there is little flux in the red from an accretion disk) except that the C iv ll5801, 5812 lines are very weak, perhaps indicating the presence of CNO-processed gas in the O star. There is no evidence of Ha emission, so the system is probably not currently undergoing Roche lobe overflow. The projected rotational velocity, km s Ϫ1 , suggests that the optical star is rotating faster than synchronously with the V sin i p 131 ‫ע‬ 6 orbit. The peculiar component of the systemic radial velocity is Ϫ km s Ϫ1 , so the system is not a runaway 17 ‫ע‬ 3 star (at least not in this dimension).

The Burst and Transient Source Experiment (BATSE) Earth Occultation Catalog of Low‐Energy Gamma‐Ray Sources

“…It is important to establish the reliability of the EOT method at these low flux levels. For example, detection of the black hole candidate LS 5039 (McSwain et al 2001) in the low-energy gamma-ray band has not been reported previously in the literature, and 4U 1812À12 was reported only for the first time in Barret et al (2003).…”

Wind Accretion and Binary Evolution of the Microquasar LS 5039

“…This high eccentricity probably results from the huge mass loss that occurred with the supernova (SN) explosion that gave birth to the compact star in the system (Bhattacharya & van den Heuvel 1991;Nelemans, Tauris, & van den Heuvel 1999). Binaries that suffer large mass loss in a SN are expected to become runaway stars, and recently both we (McSwain et al 2001b) and Ribó et al (2002) found that LS 5039 has a relatively large proper motion that indicates that the binary has a record-breaking peculiar space velocity among MXRBs.…”

“…Some kind of close interaction must have occurred because by the time of the SN the mass ratio had reversed and the separation had increased (Wellstein, Langer, & Braun 2001). Given this evidence of a pre-SN interaction, the observed C deficiency of the primary (McSwain et al 2001a) probably results from nuclear-processed gas transferred from the SN progenitor. The currently faster than synchronous rotation of the primary (McSwain et al 2001a) may correspond to the synchronous rate in the shorter period, pre-SN configuration.…”

“…L X Here we present such an analysis based on the mass-loss rate derived from our observations of the Ha profile (McSwain et al 2001a). All the parameters needed in this analysis ultimately depend on the assumed mass of the O star primary that is poorly constrained at the moment.…”

“…It has radio-emitting relativistic jets characteristic of Galactic microquasars, and it is probably a high-energy gamma-ray source as well (Paredes et al 2000). We recently discovered that the system is a short-period binary ( days) with the highest known eccentricity P p 4.117 ‫ע‬ 0.011 ( ) among O star binaries with comparable pee p 0.41 ‫ע‬ 0.05 riods (McSwain et al 2001a). This high eccentricity probably results from the huge mass loss that occurred with the supernova (SN) explosion that gave birth to the compact star in the system (Bhattacharya & van den Heuvel 1991;Nelemans, Tauris, & van den Heuvel 1999).…”