科研之友
微信
新浪微博
Facebook
分享链接
摘要
The active galactic nucleus (AGN) NGC 7213 shows a complex correlation between the monochromatic radio luminosity L-R and the 2-10 keV X-ray luminosity L-X, i.e. the correlation is unusually weak with p similar to 0 (in the form L-R proportional to L-X(p)) when L-X is below a critical luminosity, and steep with p > 1 when L-X is above that luminosity. Such a hybrid correlation in individual AGNs is unexpected as it deviates from the Fundamental Plane of AGN activity. Interestingly, a similar correlation pattern is observed in the black hole X-ray binary H1743-322, where it has been modelled by switching between different modes of accretion. We propose that the flat L-R-L-X correlation of NGC 7213 is due to the presence of a luminous hot accretion flow, an accretion model whose radiative efficiency is sensitive to the accretion rate. Given the low luminosity of the source, L-X similar to 10(-4) of the Eddington luminosity, the viscosity parameter is determined to be small, alpha approximate to 0.01. We also modelled the broad-band spectrum from radio to gamma-rays, the time lag between the radio and X-ray light curves, and the implied size and the Lorentz factor of the radio jet. We predict that NGC 7213 will enter into a two-phase accretion regime when L-X greater than or similar to 1.5 x 10(42) erg s(-1). When this happens, we predict a softening of the X-ray spectrum with the increasing flux and a steep radio/X-ray correlation.
- 出版日期2016-12
- 单位中国科学院上海天文台; 厦门大学
