CARACTERIZAÇÃO DA VARIÁVEL CATACLÍSMICA AE AQUARII VIA RAIOS X

Abstract

AE Aqr is an enigmatic Intermediate Polar, Cataclysmic Variable system. Although X-ray pulsations support the presence of an accretion column, as is typical in systems of such a class, some pieces of evidence suggest that part of the accretion may be also occurring in the outer regions by interaction with the white dwarf's magnetosphere. They are the white dwarf \textit{spin-down} ($\dot{P}_{spin} \sim 10^{-14}\,s\, s^{-1}$) inferred from the optical, non-thermal radiation observed in radio, cold and low luminous X-ray emitting plasma ($k\text{T} \sim 5\, \text{keV}$ and $L_{\text{x}; 0.3 - 10\, \text{keV}} \sim 10^{31}\,erg\,s^{-1}$), which may even have relatively low density, and the suspicion of having a non-thermal X-ray component. However, the debate about the occurrence of magnetosphere accretion in the system persists in the literature. In this work, we revisited X-ray observations of AE Aqr conducted by the NuSTAR, Swift, and XMM-\textit{Newton} satellites in the light of two novel approaches for this system, which are: (i) to verify the accordance of the X-ray emission with a cooling plasma description, which is common in accreting white dwarfs; and (ii) to investigate if there is evidence of a non-thermal component and if the reflection of primary X-rays can explain it -- either on the white dwarf surface, its accretion disk, and/or surrounding material. We show that the X-ray emission of AE Aqr can be explained by the cooling flow, provided that the reflection and strong intrinsic absorption of primary X-ray photons are considered, along with an individual thermal component. This scenario implies an accretion rate in the system of $ 10^{-11}$-$10^{-10}\, M_{\odot}/year$ and indications that the shock region of the accretion column is high, according to the low X-ray temperature and luminosity. The obtained accretion rate indicates that the magnetospheric radius is greater than the corotation radius, favoring the scenario advocated in the literature that there are two X-ray production sites in AE Aqr: one is located in outer parts of the magnetosphere and the other in a magnetic column, by the portion of the material that surpasses the magnetospheric barrier.