DAM Seminar: The Prototype of Transient X-ray Sources A0535+26/HDE245770: Time Delay between Optical and X-ray flares

Second I will discuss the optical behavior of the Bestar showing that at periastron the luminosity is typically enhanced by 0.02 toa few tenths magnitudes and the X-ray outburst occurs eight days after theperiastron. A quantitative model for this event based on a nonstationaryaccretion disk behavior, connected with a high ellipticity of the orbitalmotion has been constructed.

This model explains the observed time delaybetween the peaks of the optical and X-ray outbursts in this system by the timeof radial motion of the matter in the accretion disk, after an increase of themass flux in the vicinity of a periastral point in the binary. This time is determined by the turbulent viscositywith a parameter of a= 0.1?0.3. The increase of the mass flux is a sort of flushthat reaches the external part of the accretion disk around the neutron star,which enhances the optical luminosity.

The subsequent X-ray flare occurs whenthe matter reaches the hot central parts of the accretion disk and the neutronstar’s surface. This time delay could be ageneral behaviour of all the class of X-ray transient sources, and more.