K-Shell Emission of Neutral Iron Line from Sagittarius B2 Excited by Subrelativistic Protons

We investigated the emission of the K alpha iron line from massive molecular clouds in the galactic center (GC). We assumed that at present the total flux of this emission consists of a time-variable component generated by primary X-ray photons ejected by Sagittarius A* (Sgr A*) in the past, and a relatively weak quasi-stationary component excited by the impact of protons that were generated by star accretion onto the central black hole. The level of background emission was estimated from a rise of the 6.4 keV line intensity in the direction of several molecular clouds, which we interpreted as being a stage when the X-ray front ejected by Sgr A* entered into these clouds. Regarding the 6.4 keV emission before this intensity jump, we interpreted it as emission generated by subrelativistic cosmic rays there. The cross-section of Ka vacancies produced by protons differs from that of electrons or X-rays. Therefore, we expect that this processes can be distinguished from an analysis of the equivalent width of the iron line; also, the time variations of the width can be predicted. The line intensity from the clouds depends on their distance from Sgr A* and the coefficient of spatial diffusion near the galactic center. We expect that in a few years the line intensity for the cloud G 0.11-0.11, which is relatively close to Sgr A*, will decrease to a level of less than or similar to 10% from its present value. For the cloud Sagittarius B2 (Sgr B2) the situation is more intricate. If the diffusion coefficient is D greater than or similar to 10(27) cm(2) s(-1), the expected stationary flux should be about 10% of its level in 2000. In the opposite case the line intensity from Sgr B2 should drop down to zero because the protons do not reach the cloud.