Distinct High Energy Cutoff Variation Patterns in Two Seyfert Galaxies

• Published in: arXiv.org
• Main Authors: Kang, Jia-Lai, Wang, Jun-Xian, Kang, Wen-Yong
• Format: Paper Journal Article
• Language: English
• Published: Ithaca Cornell University Library, arXiv.org 05.01.2021
• Subjects: Physics - Astrophysics of Galaxies; Physics - High Energy Astrophysical Phenomena; Seyfert galaxies
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.2101.01497

Investigating how the cutoff energy \(E_{\rm cut}\) varies with X-ray flux and photon index \(\Gamma\) in individual AGNs opens a new window to probe the yet unclear coronal physics. So far \(E_{\rm cut}\) variations have only been detected in several AGNs but different patterns have been reported. Here we report new detections of \(E_{\rm cut}\) variations in two Seyfert galaxies with multiple NuSTAR exposures. While in NGC 3227 \(E_{\rm cut}\) monotonically increases with \(\Gamma\), the \(E_{\rm cut}\)-\(\Gamma\) relation exhibits a \(\Lambda\) shape in SWIFT J2127.4+5654 (\(E_{\rm cut}\) increasing with \(\Gamma\) at \(\Gamma\) \(\lesssim\) 2.05, but reversely decreasing at \(\Gamma\) \(\gtrsim\) 2.05), indicating more than a single underlying mechanism is involved. Meanwhile both galaxies show softer spectra while they brighten in X-ray, a common phenomenon in Seyfert galaxies. Plotting all 7 AGNs with \(E_{\rm cut}\) variations ever reported with NuSTAR observations in the \(E_{\rm cut}\)-\(\Gamma\) diagram, we find they could be unified with the \(\Lambda\) pattern. Although the sample is small and SWIFT J2127.4+5654 is the only source with \(\Gamma\) varying across the break point thus the only one exhibiting the complete \(\Lambda\) pattern in a single source, the discoveries shed new light on the coronal physics in AGNs. Possible underlying physical mechanisms are discussed.