Галина Владимировна Липунова
Государственный астрономический институт им. П.К.Штернберга МГУ им. М.В.Ломоносова
Физическое моделирование эволюции вязкого диска вокруг замагниченной нейтронной звезды: затухание вспышки 2013 г. Aql X-1
Galina Lipunova, Konstantin Malanchev, Sergey Tsygankov, Nikolai Shakura, Andrei Tavleev, Dmitry Kolesnikov.
We present a public code FREDDI (https://xray.sai.msu.ru/sciwork/) to calculate the model of a viscously evolving accretion disc around a magnetized neutron star. The model features the varying outer radius of the hot ionized part of the disc due to cooling and the varying inner radius of the disc due to interaction with the magnetosphere, hindering of accretion on the neutron star because of the centrifugal barrier, and irradiation of the outer disc and companion star by X-rays from the neutron star and disc. We consider three types of outflow from the disc inner edge: zero outflow, one based on MHD calculations, and a very efficient propeller mechanism. We compare observed light curves of the 2013 burst of Aql\,X-1 in X-ray and optical bands with modeled ones. We find that the fast drop of the $0.3-10$~keV flux can be solely explained by a radial shrinking of the hot disc. At the same time, models with the neutron star magnetic field $>10^8$~G have better fits because the accretion efficiency behaviour emphasizes the 'knee' on the light curve. We also show that a plato emission can be produced by a disc-reservoir with stalled accretion.