138 research outputs found
Spectrum of Relativistic and Subrelativistic Cosmic Rays in the 100 pc Central Region
From the rate of hydrogen ionization and the gamma ray flux, we derived the
spectrum of relativistic and subrelativistic cosmic rays (CRs) nearby and
inside the molecular cloud Sgr B2 near the Galactic Center (GC). We studied two
cases of CR propagation in molecular clouds: free propagation and scattering of
particles by magnetic fluctuations excited by the neutral gas turbulence. We
showed that in the latter case CR propagation inside the cloud can be described
as diffusion with the coefficient cm s. For
the case of hydrogen ionization by subrelativistic protons, we showed that
their spectrum outside the cloud is quite hard with the spectral index
. The energy density of subrelativistic protons ( eV cm)
is one order of magnitude higher than that of relativistic CRs. These protons
generate the 6.4 keV emission from Sgr B2, which was about 30\% of the flux
observed by Suzaku in 2013. Future observations for the period after 2013 may
discover the background flux generated by subrelativistic CRs in Sgr B2.
Alternatively hydrogen ionization of the molecular gas in Sgr B2 may be caused
by high energy electrons. We showed that the spectrum of electron
bremsstrahlung is harder than the observed continuum from Sgr B2, and in
principle this X-ray component provided by electrons could be seen from the
INTEGRAL data as a stationary high energy excess above the observed spectrum
.Comment: 42 pages, 6 figures, accepted by Ap
X-Ray Observations of the Galactic Center with Suzaku
We report on the diffuse X-ray emissions from the Galactic center (GCDX)
observed with the X-ray Imaging Spectrometer (XIS) on board the Suzaku
satellite. The highly accurate energy calibrations and extremely low background
of the XIS provide many new facts on the GCDX. These are (1) the origin of the
6.7/7.0keV lines is collisional excitation in hot plasma, (2) new SNR and
super-bubble candidates are found, (3) most of the 6.4keV line is fluorescence
by X-rays, and (4) time variability of the 6.4keV line is found from the SgrB2
complex.Comment: 4 pages, 6 figure, proceedings of the XMM-Newton workshop, June 2007,
accepted for publication in A
Exploring the dark accelerator HESS J1745-303 with Fermi Large Area Telescope
We present a detailed analysis of the gamma-ray emission from HESS J1745-303
with the data obtained by the Fermi Gamma-ray Space Telescope in the first ~29
months observation.The source can be clearly detected at the level of ~18-sigma
and ~6-sigma in 1-20 GeV and 10-20 GeV respectively. Different from the results
obtained by the Compton Gamma-ray Observatory, we do not find any evidence of
variability. Most of emission in 10-20 GeV is found to coincide with the region
C of HESS J1745-303. A simple power-law is sufficient to describe the GeV
spectrum with a photon index of ~2.6. The power-law spectrum inferred in the
GeV regime can be connected to that of a particular spatial component of HESS
J1745-303 in 1-10 TeV without any spectral break. These properties impose
independent constraints for understanding the nature of this "dark particle
accelerator".Comment: 8 pages, 3 figures, 1 table, accepted for publication in Ap
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