@Article{MaiolinoTiDAChWaOrFr:2020:PhInXR,
               author = "Maiolino, Tais and Titarchuk, Lev and D'Amico, Fl{\'a}vio and 
                         Cheng, Zhong Qun and Wang, Wei and Orlandini, Mauro and Frontera, 
                         Filippo",
          affiliation = "{Wuhan Universit} and {Universit{\`a} di Ferrara} and {Instituto 
                         Nacional de Pesquisas Espaciais (INPE)} and {Wuhan Universit} and 
                         {Wuhan Universit} and {INAF/OAS Bologna} and {Universit{\`a} di 
                         Ferrara}",
                title = "Testing Comptonization as the Origin of the Continuum in 
                         Nonmagnetic Cataclysmic Variables: The Photon Index of X-Ray 
                         Emission",
              journal = "Astrophysical Journal",
                 year = "2020",
               volume = "900",
               number = "2",
                pages = "e153",
                month = "Sept.",
             keywords = "X-ray binary stars.",
             abstract = "The X-ray spectra of nonmagnetic cataclysmic variables (nmCVs) in 
                         the similar to 0.3-15 keV energy band have been described by 
                         either one or several optically thin thermal plasma components or 
                         by cooling flow models. We tested whether the spectral continuum 
                         in nmCVs could be successfully described by Comptonization of soft 
                         photons off hot electrons presented in a cloud surrounding the 
                         source (the transition layer (TL)). We used public XMM-Newton 
                         EPIC-pn, Chandra HETG/ACIS and LETG/HRC, and RXTE PCA and HEXTE 
                         observations of four dwarf novae (U Gem, SS Cyg, VW Hyi, and SS 
                         Aur) observed in the quiescent and outburst states. In total, we 
                         analyzed 18 observations, including a simultaneous 0.4-150 keV 
                         Chandra/RXTE spectrum of SS Cyg in quiescence. We fitted the 
                         spectral continuum with up to two thermal Comptonization 
                         components (thecompTTorcompTBmodels in XSPEC) using only one 
                         thermal plasma temperature and one optical depth. In this 
                         framework, the two seed photon components are presumably coming 
                         from the innermost and outer parts of the TL (or innermost part of 
                         the disk). We obtained that the thermal Comptonization can 
                         successfully describe the spectral continuum of these nmCVs in the 
                         similar to 0.4-150 keV energy band. Moreover, we present the first 
                         principal radiative transfer model that explains the 
                         quasi-constancy of the spectral photon index observed around 1.8, 
                         which strongly supports the Comptonization framework in nmCVs.",
                  doi = "10.3847/1538-4357/abab93",
                  url = "http://dx.doi.org/10.3847/1538-4357/abab93",
                 issn = "0004-637X and 1538-4357",
             language = "en",
           targetfile = "maiolino_testing.pdf",
        urlaccessdate = "06 maio 2024"
}