Periastron accretion in high mass X-ray binaries : comparing supergiant fast X-ray transients and Be/X-ray binaries

• Main Author: Boon, Christopher Mark
• Other Authors: Bird, Antony
• Published: University of Southampton 2017
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.736723

High Mass X-ray Binaries (HXMBs) are some of the brightest objects in the X-ray sky and test our understanding of accretion physics in extreme stellar environments. In this thesis, characterisation of the accretion processes around periastron in two Supergiant Fast X-ray Transients (SFXTs) and one Be/X-ray Binary (BeXRB) is presented. A combined XMM-Newton and INTEGRAL study of the SFXT SAX J1818.6-1703 reveals the source to be in an active state, presenting a low luminosity phase that can be explained by the onset of a subsonic propeller or transition to the radiative regime of quasi-spherical accretion (QSA). The strongest flaring activity coincides with significant spectral hardening and the associated luminosities of this phase suggest a potential transition to the Compton regime of QSA. Spectral analysis also reveals strong intrinsic absorption, an order of magnitude higher than previously observed and among the highest measured in an SFXT. Observations of the SFXT IGR J18450-0435 with XMM-Newton also show low luminosity phases that can be explained by the onset of the radiative regime of QSA. Fast flaring behaviour is attributed to transition to the Compton regime and evidence of the accretion of magnetised stellar wind is presented. Spectral analysis again reveals enhanced local absorption up to five times greater than previous reported. A multi-wavelength study of the BeXRB IGR J01217-7257 allows the discovery of X-ray periodicities of 82.5±0.7 days and 2.1562±0.0001 seconds attributed to the neutron star orbital and spin periods respectively. Detected X-ray outbursts are put into an orbital context and found to be consistent with Type-I outbursts. Analysis of long-baseline optical data reveals short periodicities (∼ 1 day) that are attributed to non-radial pulsations (NRPs) of the companion and an association between the NRPs, decretion disc growth and the onset of Type-I outbursts is suggested.