Stimulated Raman scattering of water maser lines in astrophysical plasmas

Radiative transfer equations are derived and solved for the stimulated Rama n scattering of water maser lines in the astrophysical plasmas with electro ns density of about 10(6)-10(7) cm(-3). In stimulated Raman scattering, the energy of the water maser line is transferred to the side band modes: Stok es mode and anti-Stokes mode. The Stokes mode is easily produced by backwar d Raman scattering while the anti-Stokes mode is created by the interacting intersecting masers in the plasma. The intensity of the Stokes mode is hig her than that of the anti-Stokes mode. These side band modes are proposed a s explanation for the extreme velocity features observed in the galaxy NGC 4258. The threshold value of the brightness temperature for the Raman scatt ering is about 10(16)-10(19) K, and it is satisfied in the case of NGC 4258 . (C) 1999 American Institute of Physics. [S1070-664X(99)02610-5].