Long-term optical variability of high-mass X-ray binaries. II. Spectroscopy
We present the results of our monitoring program to study the long-term variability of the Halpha line in high-mass X-ray binaries. We have carried out the most complete optical spectroscopic study of the global properties of high-mass X-ray binaries so far with the analysis of more than 1100 spectra of 20 sources. Our aim is to characterise the optical variability timescales and study the interaction between the neutron star and the accreting material. Our results can be summarised as follows: i) we find that Be/X-ray binaries with narrow orbits are more variable than systems with long orbital periods, ii) we show that a Keplerian distribution of the gas particles provides a good descripti…
Correlated optical/X-ray variability in the high-mass X-ray binary SAX J2103.5+4545
SAX J2103.5+4545 is the Be/X-ray binary with the shortest orbital period. It shows extended bright and faint X-ray states that last for a few hundred days. The main objective of this work is to investigate the relationship between the X-ray and optical variability and to characterise the spectral and timing properties of the bright and faint states. We have found a correlation between the spectral and temporal parameters that fit the energy and power spectra. Softer energy spectra correspond to softer power spectra. That is to say, when the energy spectrum is soft the power at high frequencies is suppressed. We also present the results of our monitoring of the Halpha line of the optical cou…
New insights into the Be/X-ray binary system MXB 0656-072
The X-ray transient MXB 0656-072 is a poorly studied member of high-mass X-ray binaries. Based on the transient nature of the X-ray emission, the detection of pulsations, and the early-type companion, it has been classified as a Be X-ray binary (Be/XRB). However, the flaring activity covering a large fraction of a giant outburst is somehow peculiar. Our goal is to investigate the multiwavelength variability of the high-mass X-ray binary MXB 0656-072. We carried out optical spectroscopy and analysed all RXTE archive data, performing a detailed X-ray-colour, spectral, and timing analysis of both normal (type-I) and giant (type-II) outbursts from MXB 0656-072 This is the first detailed analysi…