Ignacio Negueruela: Multiwavelength observations of HMXBs: Constraints on the accretion environment of neutron stars

Most HMXBs are X-ray pulsars, and strong magnetic fields somehow inhibit jet formation, so no radio emission is detected. The nature of the donor determines the main properties of the HMXB, and low resolution spectroscopy in the optical, or IR (if optically obscured), is used to characterise the donor. High quality spectra are needed to determine luminocity class and mass loss rate, but this is difficult (especially in IR) as large telescopes are needed.

In some HMXBs, the orbital parameters can be determined. For SMC X-1, the neutron star mass is quite robustly shown to be less than 1.2 solar masses, in line with a general trend of neutron stars in HMXBs being less massive than those in LMXBs (though mass errors are large, and the sample small). The mass of the donor star in 4U1700-37 is measured to be 58 solar masses, so it appears that not all massive stars form black holes. The neutron star in this HMXB is found to be 2.4 solar masses, though the errors are large.