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Date and Time of the Query: 2019-08-21 T11:57:23 PDT
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For refcode 2018ApJ...863...71Z:
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2018ApJ...863...71Z On Measuring the Variation of High-energy Cutoff in Active Galactic Nuclei Zhang, Ji-Xian; Wang, Jun-Xian; Zhu, Fei-Fan Abstract. The variation in the high-energy cutoff, E_ c_, in active galactic nuclei (AGNs) uniquely probes the corona physics. In this work, we show that the ratio of two NuSTAR spectra (analogous to the difference-imaging technique widely used in astronomy) is uniquely useful in studying E_ c_ variations. The spectra ratio could directly illustrate potential E_ c_ variation between two spectra. By comparing with the ratio of two spectral-fitting models, it also examines the reliability of the spectral fitting measured E_ c_ variation. Assisted with this technique, we revisit the five AGNs in the literature (MCG-5-23-16, 3C 382, NGC 4593, NGC 5548, and Mrk 335), for which E_ c_ (kT_ e_) variations have been claimed with NuSTAR observations. We show that the claimed E_ c_ variations appear inconsistent with the spectra ratios in three of them, thus they need to be revised, demonstrating the striking usefulness of spectra ratio. We present thereby improved spectral-fitting results and E_ c_ variations. We also report a new source with E_ c_ variations based on NuSTAR observations (radio galaxy 4C+74.26). We find the corona tends to be hotter when it brightens (hotter-when-brighter) in 3C 382, NGC 5548, Mrk 335, and 4C+74.27, but MCG-5-23-16 and NGC 4593 show no evidence of significant E_ c_ variations. Meanwhile, all six sources in this small sample appear softer when brighter. Changes in corona geometry are required to explain the observed hotter-when-brighter trends. Key words: galaxies: active, quasars: individual: 4C+74.26, X-rays: individual: 4C+74.26
Retrieve 6 NED objects in this reference.
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