The Large Amplitude X-ray Variability in NGC 7589: Possible Evidence for Accretion Mode Transition

• Published in: arXiv.org 2019-12
• Main Authors: Liu, Zhu, He-Yang, Liu, Cheng, Huaqing, Qiao, Erlin, Yuan, Weimin
• Format: Article
• Language: English
• Subjects: Accretion disks; Active galactic nuclei; Amplitudes; Blackbody; Deposition; Luminosity; Soft x rays; X ray binaries; X ray stars; XMM (spacecraft)
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.1912.01897

We report the discovery of large amplitude X-ray variability in the low luminosity AGN (LLAGN) MGC 7589, and present possible observational evidence for accretion mode transition in this source. Long-term X-ray flux variations by a factor of more than 50 are found using X-ray data obtained by Swift/XRT and XMM-Newton over 17 years. Results of long-term monitoring data in the UV, optical and infrared bands over ~20 years are also presented. The Eddington ratio increased from \(10^{-3}\) to \(\sim0.13\), suggesting a transition of the accretion flow from an ADAF to a standard thin accretion disc. Further evidence supporting the thin disc in the high luminosity state is found by the detection of a significant soft X-ray component in the X-ray spectrum. The temperature of this component (\(\sim19^{+15}_{-7}\)eV, fitted with a blackbody model) is in agreement with the predicted temperature of the inner region for a thin disc around a black hole (BH) with mass of \(\sim10^{7}\,M_{\mathrm{Sun}}\). These results may indicate that NGC 7589 had experienced accretion mode transition over a timescale of a few years, suggesting the idea that similar accretion processes are at work for massive black hole and black hole X-ray binaries.