Does the Iron K${}_{\alpha }$ Line of Active Galactic Nuclei Arise from the Cerenkov Line-like Radiation?

Abstract

When thermal relativistic electrons with isotropic distribution of velocities move in a gas region, or impinge upon the surface of a cloud that consists of a dense gas or doped dusts, the Cerenkov effect produces peculiar atomic or ionic emission lines -- the Cerenkov line-like radiation. This newly recognized emission mechanism may find wide applications in high-energy astrophysics. In this paper, we tentatively adopt this new line emission mechanism to discuss the origin of iron K${}_{\alpha }$ feature of AGNs. Motivation of this research is to attempt a solution to a problem encountered by the ``disk-fluorescence line'' model, i.e. the lack of temporal response of the observed iron K${}_{\alpha }$ line flux to the changes of the X-ray continuum flux. If the Cerenkov line emission is indeed responsible significantly for the iron K${}_{\alpha }$ feature, the conventional scenario around the central supermassive black holes of AGNs would need to be modified to accommodate more energetic, more violent and much denser environments than previously thought.

22 pages, 4 figures, 1 table. ApJ in press (December)

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• Imaging Bright Spots in the Accretion Flow Near the Black Hole Horizon of Sgr A*
• Spectral Analysis of the Accretion Flow in NGC 1052 with Suzaku
• Testing General Relativity with High-Resolution Imaging of Sgr A*