Ponent: Dr. Franco Giovannelli ( INAF-Istituto di Astrofisica e Planetologia Spaziali- Roma)
Data / hora: 20.06.2014, 11:30:00
Lloc: Seminari planta 7, Departament d'Astronomia i Meteorologia, Facultat de Física
Resum: First I will describe the multifrequency behaviour of the transient X-ray source A0535+26/HDE245770 and its association with the SNR S147.
Second I will discuss the optical behavior of the Be star showing that at periastron the luminosity is typically enhanced by 0.02 to a few tenths magnitudes and the X-ray outburst occurs eight days after the periastron. A quantitative model for this event based on a nonstationary accretion disk behavior, connected with a high ellipticity of the orbital motion has been constructed. This model explains the observed time delay between the peaks of the optical and X-ray outbursts in this system by the time of radial motion of the matter in the accretion disk, after an increase of the mass flux in the vicinity of a periastral point in the binary.
This time is determined by the turbulent viscosity with a parameter of a = 0.1−0.3. The increase of the mass flux is a sort of flush that reaches the external part of the accretion disk around the neutron star, which enhances the optical luminosity. The subsequent X-ray flare occurs when the matter reaches the hot central parts of the accretion disk and the neutron star’s surface.
This time delay could be a general behaviour of all the class of X-ray transient sources, and more.