INDUCING INTRINSIC γ-RAY EMISSION OF THE INTERSTELLAR MEDIUM BY INTENSE FLUXES OF PROTONS AND α-PARTICLES IN ACTIVE GALACTIC NUCLEI

Анотація

Cosmic-ray induced γ-ray emission in
active galactic nuclei (AGN) has been examined in this
study for the first time. Cross-sections for the formation of
γ-quanta in such cosmic-ray collisions were selected in the
1-150 MeV energy range. Synthetic γ-ray spectra were
computed for both interstellar gas and dust. At the same
energies of particle collisions and induced emission of γ-
quanta, energy intervals of diagnostic interest were
determined. Specific characteristics of emission were
detected in the energy ranges of 5-15 MeV and 23-30 MeV
for most investigated elements. Diffuse continuous γ-ray
spectra for the other energy ranges were less informative
with regard to the determination of the chemical
composition of interstellar gas. It has been shown that
exploring cosmic-ray fluxes in the vicinity of galactic
centres by employing the examined γ-ray spectra yields a
pattern of their energy distribution. Diagrams of cross-
sections for γ-quanta formation were computed for the α-
process elements. Synthetic γ-ray spectra of interstellar gas
and dust were calculated individually and collectively. It
has been indicated that, under certain conditions in AGN,
cross-sections for ionisation of atoms due to energy losses
by cosmic-ray induced ionisation and γ-quanta emission
resulting from collisions with cosmic rays are similar. It has
been found that when the maximum of proton and α-
particle energy distribution function falls within the
investigated range of energies, it leads to the formation of
the peak flux of γ-rays. This is particularly important for
the interpretation of observations in the energy ranges of 5-
15 MeV and 23-30 MeV. Synthetic induced γ-ray spectra
of interstellar dust were computed, and methods of their
observations for silicate and carbon-containing dust, which
account for 80% and 20% of the interstellar-dust total mass,
respectively, were determined. It has been deduced that the
contribution of Compton processes to γ-quanta emission
can be neglected at the investigated energies.