The origin of the soft excess in the luminous quasar HE 1029-1401
Résumé
The enigmatic and intriguing phenomenon of the “soft excess” observed in the X-ray spectra of luminous quasars continues to be a subject of considerable interest and debate in the field of high-energy astrophysics. This study focuses on the quasar HE 1029-1401 ( z = 0.086, log( L bol /[erg s −1 ]) = 46.0 ± 0.2), with a particular emphasis on investigating the properties of the hot corona and the physical origin of the soft excess. In this study, we present the results of a joint XMM-Newton / NuSTAR monitoring campaign of this quasar conducted in May 2022. The source exhibits a cold and narrow Fe K α emission line at 6.4 keV, in addition to the detection of a broad component. Our findings suggest that the soft excess observed in HE 1029-1401 can be adequately explained by Comptonized emission originating from a warm corona. Specifically, fitting the spectra with two N THCOMP component we found that the warm corona is characterized by a photon index (Γ w ) of 2.75 ± 0.05 and by an electron temperature ( kT e w ) of 0.39 −0.04 +0.06 keV, while the optical depth ( τ w ) is found to be 23 ± 3. We also test more physical models for the warm corona, corresponding to two scenarios: pure Comptonization and Comptonization plus reflection. Both models provide a good fit to the data, and are in agreement with a radially extended warm corona having a size of a few tens of gravitational radii.
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