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The X-Ray Coronae in NuSTAR Bright Active Galactic Nuclei
Ist Teil von
The Astrophysical journal, 2022-04, Vol.929 (2), p.141
Ort / Verlag
Philadelphia: The American Astronomical Society
Erscheinungsjahr
2022
Quelle
EZB Electronic Journals Library
Beschreibungen/Notizen
Abstract
We present a systematic and uniform analysis of NuSTAR data of a sample of 60 SWIFT BAT-selected AGNs with 10–78 keV signal-to-noise ratio (S/N) > 50, 10 of which are radio loud. We measure their high-energy cutoff
E
cut
or coronal temperature
T
e
using three different spectral models to fit their NuSTAR spectra and show that a threshold in NuSTAR spectral S/N is essential for such measurements. High-energy spectral breaks are detected in the majority of the sample, and for the rest, strong constraints on
E
cut
or
T
e
are obtained. Strikingly, we find extraordinarily large
E
cut
lower limits (>400 keV, up to >800 keV) in 10 radio-quiet sources, whereas we find none in the radio-loud sample. Consequently and surprisingly, we find a significantly larger mean
E
cut
/
T
e
of radio-quiet sources compared with radio-loud ones. The reliability of these measurements is carefully inspected and verified with simulations. We find a strong positive correlation between
E
cut
and photon index Γ, which cannot be attributed to the parameter degeneracy. The strong dependence of
E
cut
on Γ, which could fully account for the discrepancy of the
E
cut
distribution between radio-loud and radio-quiet sources, indicates that the X-ray coronae in AGNs with steeper hard X-ray spectra have on average higher temperature and thus smaller opacity. However, no prominent correlation is found between
E
cut
and
λ
edd
. In the
l
–Θ diagram, we find a considerable fraction of sources lie beyond the boundaries of forbidden regions due to runaway pair production, posing (stronger) challenges to various (flat) coronal geometries.