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Spectral Fittings of Warm Coronal Radiation with High Seed Photon Temperature: Apparent Low-temperature and Flat Soft Excess in AGNs

A warm corona has been widely proposed to explain the soft excess (SE) in X-ray above the 2–10 keV power law extrapolation in Active Galactic Nuclei (AGNs). In actual spectral fittings, the warm coronal seed photon temperature ( T s ) is usually assumed to be far away from the soft X-ray, but kT s c...

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Bibliographic Details
Published in:Research in astronomy and astrophysics 2024-07, Vol.24 (7), p.75010
Main Authors: Tang, Ze-Yuan, Feng, Jun-Jie, Fan, Jun-Hui
Format: Article
Language:English
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Summary:A warm corona has been widely proposed to explain the soft excess (SE) in X-ray above the 2–10 keV power law extrapolation in Active Galactic Nuclei (AGNs). In actual spectral fittings, the warm coronal seed photon temperature ( T s ) is usually assumed to be far away from the soft X-ray, but kT s can reach close to 0.1 keV in the standard accretion disk model. In this study, we used Monte Carlo simulations to obtain radiation spectra from a slab-like warm corona and fitted the spectra using the spherical-geometry-based routine thcomp or a thermal component. Our findings reveal that high T s can influence the fitting results. A moderately high kT s (around 0.03 keV) can result in an apparent low-temperature and flat SE, while an extremely high kT s (around 0.07 keV) can even produce an unobserved blackbody-like SE. Our conclusions indicate that, for spectral fittings of the warm coronal radiation (SE in AGNs), kT s should be treated as a free parameter with an upper limit, and an accurate coronal geometry is necessary when kT s > 0.01 keV.
ISSN:1674-4527
2397-6209
DOI:10.1088/1674-4527/ad4fc5