6,355 research outputs found
High energy cosmic ray self-confinement close to extragalactic sources
The ultra-high energy cosmic rays observed at the Earth are most likely
accelerated in extra-galactic sources. For the typical luminosities invoked for
such sources, the electric current associated to the flux of cosmic rays that
leave them is large. The associated plasma instabilities create magnetic
fluctuations that can efficiently scatter particles. We argue that this
phenomenon forces cosmic rays to be self-confined in the source proximity for
energies , where GeV
for low background magnetic fields (). For larger values of
, cosmic rays are confined close to their sources for energies GeV, where
is the field in units of nG, is its coherence
lengths in units of 10 Mpc and is the source luminosity in units of
erg/s.Comment: To Appear in Physical Review Letter
Contribution to diffuse gamma-ray emission coming from self-confined CRs around their Galactic sources
Recent observations of the diffuse Galactic gamma-ray emission by the
Fermi-LAT satellite have shown significant deviations from models which assume
the same diffusion properties for cosmic rays (CR) throughout the Galaxy. We
explore the possibility that a fraction of this diffuse Galactic emission could
be due to hadronic interactions of CRs self-confined in the region around their
sources. In fact, freshly accelerated CRs that diffuse away from the
acceleration region can trigger the streaming instability able to amplify
magnetic disturbance and to reduce the particle diffusion. When this happen,
CRs are trapped in the near source region for a time longer than expected and
an extended gamma-ray halo is produces around each source. Here we calculate
the contribution to the diffuse gamma-ray background due to the overlap along
lines of sight of several of these extended halos. We find that if the density
of neutrals is low, the halos can account for a substantial fraction of the
diffuse emission observed by Fermi-LAT, depending on the orientation of the
line of sight with respect to the direction of the galactic center.Comment: 8 pages, 2 figs. Proceeding the 35th International Cosmic Ray
Conference (ICRC2017), Bexco, Busan, Kore
Finiteness of 2D Topological BF-Theory with Matter Coupling
We study the ultraviolet and the infrared behavior of 2D topological
BF-Theory coupled to vector and scalar fields. This model is equivalent to 2D
gravity coupled to topological matter. Using techniques of the algebraic
renormalization program we show that this model is anomaly free and ultraviolet
as well as infrared finite at all orders of perturbation theory.Comment: 17 pages, Late
General Solution Of Linear Vector Supersymmetry
We give the general solution of the Ward identity for the linear vector
supersymmetry which characterizes all topological models. Such solution, whose
expression is quite compact and simple, greatly simplifies the study of
theories displaying a supersymmetric algebraic structure, reducing to a few
lines the proof of their possible finiteness. In particular, the cohomology
technology usually involved for the quantum extension of these theories, is
completely bypassed. The case of Chern-Simons theory is taken as an example.Comment: 18 pages, LaTeX, no figure
Vector Supersymmetry of 2D Yang-Mills Theory
The vector supersymmetry of the 2D topological BF model is extended to 2D
Yang-Mills. The consequences of the corresponding Ward identity on the
ultraviolet behavior of the theory are analyzed.Comment: Some references adde
Thermal conductivity distributed from a Thermal Response Test (TRT) in a borehole heat exchanger (BHE)
The Thermal Response Test (TRT) is the most versatile tool to determine the thermal propriety of the underground for designing and sizing of the borehole heat exchangers (BHE). The TRT permits to get the average thermal conductivity (λ) across the whole stratigraphy, the thermal resistance (Rb) of the borehole / grout / rocks and the undisturbed temperature of the soil (Tg). The ground temperature is influenced by climate, topographical, geological and hydrological factors. Vertical temperature changes allows to get the relationships with the lithology and especially with the groundwater. Vertical temperature log, acquired during and after the TRT, permits to calculate the distributed thermal conductivity over each stratigraphic interval. This method permits to verify how the different lithologies and the groundwater contribute to the heat exchange in the borehole/ground system, so called geoexchange. The experimental site test indicates that the marls and clayed-marls levels show a higher thermal inertia than the sandstone ones and then lower values of thermal conducivity. The sandstones have a higher thermal conductivity with a rapid cooling and they provide the main contribution to the ground heat exchange. The distributed thermal conductivity is an useful tool for designing the BHE with the best performance, a better economic return and with low environmental impacts
Discovery of diffuse radio emission at the center of the most X-ray-luminous cluster RX J1347.5-1145
We report on new VLA radio observations of the distant cluster RX
J1347.5-1145, which is the most luminous in X-rays. We aim at investigating the
possible presence of diffuse and extended radio emission in this very peculiar
system which shows both a massive cooling flow and merging signatures. New low
resolution (~18 arcsec) VLA radio observations of this cluster are combined
with higher resolution (~2 arcsec) data available in the VLA archive. We
discover the presence of a diffuse and extended (~500 kpc) radio source
centered on the cluster, unrelated to the radio emission of the central AGN.
The properties of the radio source, in particular a) its occurrence at the
center of a massive cooling flow cluster, b) its total size comparable to that
of the cooling region, c) its agreement with the observational trend between
radio luminosity and cooling flow power, indicate that RX J1347.5-1145 hosts a
radio mini-halo. We suggest that the radio emission of this mini-halo, which is
the most distant object of its class discovered up to now, is due to electron
re-acceleration triggered by the central cooling flow. However, we also note
that the morphology of the diffuse radio emission shows an elongation
coincident with the position of a hot subclump detected in X-rays, thus
suggesting that additional energy for the electron re-acceleration might be
provided by the submerger event.Comment: 5 pages, 6 figures, accepted for publication in A&A Letter
Identifying Nearby UHECR Accelerators using UHE (and VHE) Photons
Ultra-high energy photons (UHE, E > 10^19 eV) are inevitably produced during
the propagation of 10^20 eV protons in extragalactic space. Their short
interaction lengths (<20 Mpc) at these energies, combined with the impressive
sensitivity of the Pierre Auger Observatory detector to these particles, makes
them an ideal probe of nearby ultra-high-energy cosmic ray (UHECR) sources. We
here discuss the particular case of photons from a single nearby (within 30
Mpc) source in light of the possibility that such an object might be
responsible for several of the UHECR events published by the Auger
collaboration. We demonstrate that the photon signal accompanying a cluster of
a few > 6x10^19 eV UHECRs from such a source should be detectable by Auger in
the near future. The detection of these photons would also be a signature of a
light composition of the UHECRs from the nearby source.Comment: 4 pages, 2 figures, accepted for publication in PR
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