Oral Presentation

Evidence of accretion mode transition in the low luminosity AGN NGC 7589

Author(s): Zhu Liu (NAOC), Weimin Yuan (NAOC), Heyang Liu (NAOC)

Presenter: Zhu Liu (National Astronomical Observatories, CAS)

We report the evidence for accretion mode transitions in a low luminosity AGN (LLAGN) NGC 7589 (spectroscopically calssified as Seyfert 1.9 or LINERS) from X-ray spectral analysis as well as multiple bands temporal study. Multibands long-term light curves suggest that NGC 7589 underwent several outbursts during the past three decades. A large amplitude X-ray variability by a factor of ~50 is shown in the long-term X-ray light curve. At its lowest luminosity, detected by ROSAT in 1995 and Swift/XRT in 2018, the Eddington ratio is estimated to be less than1E-3, consistent with the RIAF accretion mode, while it increased to a few per cent at its highest X-ray luminosity observed by Swift/XRT in June 2006. A significant Narrow Fe K line is detected in the 2006 XMM-Newton observation which has the highest X-ray luminosity observed by XMM-Newton. The large equivalent width of the line, i.e. 523^{+293}_{-282} eV, may indicate that the line is produce in the outer region of the accretion disc. Evidence of a blackbody component with temperature of 31eV is found in the April 2006 Swift/XRT observation which detected the highest X-ray luminosity so far, implying that the disc extends to the inner region close to the BH and the RIAF accretion mode transients to a standard thin accretion disc.