Navegando por Autor "Silva, Karleyne Medeiros Gomes da"

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    Breaking the Degeneracy in Magnetic Cataclysmic Variable X-Ray Spectral Modeling Using X-Ray Light Curves
    (IOP science) Belloni, Diogo; Rodrigues, Claudia Vilega; Schreiber, Matthias R.; Castro, Manuel; Costa, Joaquim Eduardo Rezende; Hayashi, Takayuki; Lima, Isabel de Jesus; Luna, Gerardo Juan Manuel; Martins, Murilo; Oliveira, Alexandre Soares de; Parsons, Steven G.; Silva, Karleyne Medeiros Gomes da; Stecchini, Paulo Eduardo; Stuchi, Teresa de Jesus; Zorotovic, Monica
    We present an analysis of mock X-ray spectra and light curves of magnetic cataclysmic variables using an upgraded version of the 3D cyclops code. This 3D representation of the accretion flow allows us to properly model total and partial occultation of the postshock region by the white dwarf as well as the modulation of the X-ray light curves due to the phase-dependent extinction of the preshock region. We carried out detailed postshock region modeling in a four-dimensional parameter space by varying the white dwarf mass and magnetic field strength as well as the magnetosphere radius and the specific accretion rate. To calculate the postshock region temperature and density profiles, we assumed equipartition between ions and electrons; took into account the white dwarf gravitational potential, the finite size of the magnetosphere, and a dipole-like magnetic field geometry; and considered cooling by both bremsstrahlung and cyclotron radiative processes. By investigating the impact of the parameters on the resulting X-ray continuum spectra, we show that there is an inevitable degeneracy in the four-dimensional parameter space investigated here, which compromises X-ray continuum spectral fitting strategies and can lead to incorrect parameter estimates. However, the inclusion of X-ray light curves in different energy ranges can break this degeneracy, and it therefore remains, in principle, possible to use X-ray data to derive fundamental parameters of magnetic cataclysmic variables, which represents an essential step toward understanding their formation and evolution.
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    Detection of the White Dwarf Spin of the Long-orbital Period Magnetic Cataclysmic Variable V1082 Sgr
    (American Astronomical Society) Lima, Isabel de Jesus; Tovmassian, Gagik; Rodrigues, Claudia Vilega; Oliveira, Alexandre Soares de; Luna, Gerardo Juan Manuel; Buckley, David A. H.; Silva, Karleyne Medeiros Gomes da; Figueiredo, Ana Carolina Mattiuci; Souza, Diego Carvalho de; Schlindwein, Wagner; Marques, Fernando Falkenberg; Palhares, Matheus Soares
    We report on the discovery of circular polarization modulated with a period of 1.943 ± 0.002hr in the cataclysmic variable V1082 Sgr. These findings unambiguously reveal the rotation of a magnetic white dwarf and establish its intermediate polar nature. Along with its extraordinary long orbital period (Porb) of 20.8 hr, the spin period (Pspin) places this system in an extreme position of the Pspin versus Porb distribution. The circular polarization phase diagram has a single peak and an amplitude smaller than 1%. These data were used to model the postshock region of the accretion flow on the white dwarf surface using the CYCLOPS code. We obtained a magnetic field in the white dwarf pole of 11 MG and a magnetospheric radius consistent with the coupling region at around 2–3 white dwarf radii. The Pspin/Porb value and the estimated magnetic field momentum suggest that V1082 Sgr could be out of spin equilibrium or in a spin-up state, possibly in a stream accretion mode.