1,597 research outputs found
Diffuse cosmic rays shining in the Galactic center: A novel interpretation of H.E.S.S. and Fermi-LAT gamma-ray data
We present a novel interpretation of the -ray diffuse emission
measured by Fermi-LAT and H.E.S.S. in the Galactic center (GC) region and the
Galactic ridge (GR). In the first part we perform a data-driven analysis based
on PASS8 Fermi-LAT data: we extend down to few GeV the spectra measured by
H.E.S.S. and infer the primary cosmic-ray (CR) radial distribution between 0.1
and 3 TeV. In the second part we adopt a CR transport model based on a
position-dependent diffusion coefficient. Such behavior reproduces the radial
dependence of the CR spectral index recently inferred from the Fermi-LAT
observations. We find that the bulk of the GR emission can be naturally
explained by the interaction of the diffuse steady-state Galactic CR sea with
the gas present in the Central Molecular Zone. Although our results leave room
for a residual radial-dependent emission associated with a central source, the
relevance of the large-scale background prevents from a solid evidence of a GC
Pevatron.Comment: 5 pages, 3 figures, accepted for publication in Physical Review
Letter
Hard Cosmic Ray Sea in the Galactic Center: a consistent interpretation of H.E.S.S. and Fermi-LAT -ray data
We present a novel interpretation of the gamma-ray diffuse emission measured
by H.E.S.S. in the Galactic Center (GC) region and the Galactic ridge. Our
starting base is an updated analysis of PASS8 Fermi-LAT data, which allows to
extend down to few GeV the spectra measured by H.E.S.S. and to infer the
primary CR radial distribution above 100 GeV. We compare those results with a
CR transport model assuming a harder scaling of the diffusion coefficient with
rigidity in the inner Galaxy. Such a behavior reproduces the radial dependence
of the CR spectral index recently inferred from Fermi-LAT measurements in the
inner GP. We find that, in this scenario, the bulk of the Galactic ridge
emission can be naturally explained by the interaction of the diffuse,
steady-state Galactic CR sea interacting with the gas present in the Central
molecular zone. The evidence of a GC PeVatron is significantly weaker than that
inferred adopting a conventional (softer) CR sea.Comment: Oral contribution to the International Cosmic Ray Conference (ICRC
2017), 12-20 July 2017, Bexco, Busan, Kore
Gradual transition from insulator to semimetal of CaEuB with increasing Eu concentration
The local environment of Eu (, ) in
CaEuB () is investigated by
means of electron spin resonance (ESR). For the spectra show
resolved \textit{fine} and \textit{hyperfine} structures due to the cubic
crystal \textit{electric} field and nuclear \textit{hyperfine} field,
respectively. The resonances have Lorentzian line shape, indicating an
\textit{insulating} environment for the Eu ions. For , as increases, the ESR lines broaden due to local
distortions caused by the Eu/Ca ions substitution. For , the lines broaden further and the spectra gradually change from
Lorentzian to Dysonian resonances, suggesting a coexistence of both
\textit{insulating} and \textit{metallic} environments for the Eu ions.
In contrast to CaGdB, the \textit{fine} structure is still
observable up to . For the \textit{fine} and
\textit{hyperfine} structures are no longer observed, the line width increases,
and the line shape is purely Dysonian anticipating the \textit{semimetallic}
character of EuB. This broadening is attributed to a spin-flip scattering
relaxation process due to the exchange interaction between conduction and
Eu electrons. High field ESR measurements for
reveal smaller and anisotropic line widths, which are attributed to magnetic
polarons and Fermi surface effects, respectively.Comment: Submitted to PR
A hadronic scenario for the galactic ridge
Several observations from Fermi-LAT, up to few hundred GeV, and from H.E.S.S., up to - 10 TeV, reported an intense γ-ray emission from the inner part of the Galactic plane. After the subtraction of point-like contributions, the remaining γ-ray spectrum can provide important hints about the cosmic-ray (CR) population in that region. In particular, the diffuse spectrum measured by both Fermi-LAT and H.E.S.S. in the Galactic Ridge is significantly harder with respect to the rest of the Galaxy. These results were recently interpreted in terms of a comprehensive CR transport model which, adopting a spatial dependent diffusion coefficient and convective velocity, reproduces Fermi-LAT results on the whole sky as well as local CR spectra. We showed as that model predicts a significantly harder neutrino diffuse emission compared to conventional scenarios: The predicted signal is able to account for a significant fraction of the astrophysical flux measured by IceCube. In this contribution, we use the same setup to calculate the expected neutrino flux from several windows in the inner Galactic plane and compare the results with IceCube observations and the sensitivities of Mediterranean neutrino telescopes. In particular, for the ANTARES experiment, we compare the model expectations with the upper limits obtained from a recent unblinded data-analysis focused on the galactic ridge region. Moreover, we also show the expectations from the galactic ridge for the future KM3NeT observatory, whose position is optimal to observe this portion of the sky
- …