43 research outputs found
Diffuse Gamma-ray Emission from the Galactic Center - A Multiple Energy Injection Model
We suggest that the energy source of the observed diffuse gamma-ray emission
from the direction of the Galactic center is the Galactic black hole Sgr A*,
which becomes active when a star is captured at a rate of
yr^{-1}. Subsequently the star is tidally disrupted and its matter is accreted
into the black hole. During the active phase relativistic protons with a
characteristic energy erg per capture are ejected. Over
90% of these relativistic protons disappear due to proton-proton collisions on
a timescale years in the small central bulge region with
radius pc within Sgr A*, where the density is cm^{-3}. The
gamma-ray intensity, which results from the decay of neutral pions produced by
proton-proton collisions, decreases according to , where t is
the time after last stellar capture. Less than 5% of relativistic protons
escaped from the central bulge region can survive and maintain their energy for
>10^7 years due to much lower gas density outside, where the gas density can
drop to cm. They can diffuse to a pc region before
disappearing due to proton-proton collisions. The observed diffuse GeV
gamma-rays resulting from the decay of neutral pions produced via collision
between these escaped protons and the gas in this region is expected to be
insensitive to time in the multi-injection model with the characteristic
injection rate of 10^{-5} yr^{-1}. Our model calculated GeV and 511 keV
gamma-ray intensities are consistent with the observed results of EGRET and
INTEGRAL, however, our calculated inflight annihilation rate cannot produce
sufficient intensity to explain the COMPTEL data.Comment: 8 pages, 3 figures, accepted by A&
Broad-band nonthermal emission from molecular clouds illuminated by cosmic rays from nearby supernova remnants
Molecular clouds are expected to emit non-thermal radiation due to cosmic ray
interactions in the dense magnetized gas. Such emission is amplified if a cloud
is located close to an accelerator of cosmic rays and if energetic particles
can leave the accelerator site and diffusively reach the cloud. We consider
here the situation in which a molecular cloud is located in the proximity of a
supernova remnant which is efficiently accelerating cosmic rays and gradually
releasing them in the interstellar medium. We calculate the multiwavelength
spectrum from radio to gamma rays which is emerging from the cloud as the
result of cosmic ray interactions. The total energy output is dominated by the
gamma ray emission, which can exceed the emission in other bands by an order of
magnitude or more. This suggests that some of the unidentified TeV sources
detected so far, with no obvious or very weak counterparts in other
wavelengths, might be in fact associated with clouds illuminated by cosmic rays
coming from a nearby source. Moreover, under certain conditions, the gamma ray
spectrum exhibit a concave shape, being steep at low energies and hard at high
energies. This fact might have important implications for the studies of the
spectral compatibility of GeV and TeV gamma ray sources.Comment: 13 pages, 6 figures, submitted to MNRA