Special astrophysical observatory RAS, S.Petersburg branch
Nonlinear processes of interaction of electromagnetic field with matter, that appears in high orders of perturbation theory, are considerable only under strong electromagnetic fields. They are of particular astrophysical interest, because permit us to measure the radiation intensity directly in the region of scattering (and, for example, to obtain independent estimation of distance to the object). It become possible due to nonlinear dependence of the scattering probability on the field intensity. At present paper the nonlinear scattering of maser (gigamaser) radiation by free electrons in neighbor HII - region, which is accompanied by absorption of two photons at main frequency and emission of one photon at doubled one, is considered. The Thomson, double Compton and free-free scattering of the maser radiation in ionized gas were taking into account. It is shown that the fluxes from gigamasers take place in AGNs, must be 10-7 - 10-8 Jy (without possible amplification of the line). It is stressed that in the non - LTE case, the line should be significantly amplified. It is well known, the luminosity of OH gigamaser is correlated with square of IR- luminosity of host galaxy. For this reason, bright IR galaxies are of interest to find out the line at doubled frequency 3.3 GHz. In the most probable case, when observer is out of solid angle of the main maser emission, weak unsaturated lines at main frequency and broad (106 IJ) line at doubled one (due to nonlinear scattering) can be observed.