Reflection of radio radiation at ionization fronts in emission line regions and accretion disks of active galactic nuclei

Abstract

It is known that high frequency short duration electromagnetic pulses can be generated by reflection of low frequency radiation off relativistically moving ionization fronts. In addition, a part of the incident electromagnetic energy is converted into a spatially periodic static magnetic field. Here, we investigate this phenomenon in the emission line region (ELR) and accretion disks of active galactic nuclei (AGN) where relativistically moving ionization fronts are created by the ionizing continuum. It is suggested that this process may play an essential role in (1) causing rapid correlated variability in radio radiation and high frequency parts of the nonthermal spectrum; (2) generating high frequency radiation through scattering of relativistic electrons off the spatially periodic magnetic field, a byproduct of the reflection process; (3) the diagnostic of the emission line region; and (4) absorption of the radio radiation. The anomalous absorption of radio radiation in ELR through parametric decay instabilities has been pointed out earlier. Interaction of radio radiation with ionization fronts further strengthens the case for the existence of strong correlation between the nonthermal radio continuum and the ELR phenomena as the multiwavelength observations of AGN are beginning to do.