6 research outputs found
On The {\it Fermi} -Lat Surplus of the Diffuse Galactic Gamma-Ray Emission
Recent observations of the diffuse Galactic \gr emission (DGE) by the {\it
Fermi} Large Area Telescope ({\it Fermi}-LAT) have shown significant
deviations, above a few GeV until about 100 GeV, from DGE models that use the
GALPROP code for the propagation of cosmic ray (CR) particles outside their
sources in the Galaxy and their interaction with the target distributions of
the interstellar gas and radiation fields. The surplus of radiation observed is
most pronounced in the inner Galaxy, where the concentration of CR sources is
strongest. The present study investigates this "{\it Fermi}-LAT Galactic Plane
Surplus" by estimating the \gr emission from the sources themselves, which is
disregarded in the above DGE models. It is shown that indeed the expected hard
spectrum of CRs, still confined in their sources (SCRs), can explain this
surplus. The method is based on earlier studies regarding the so-called EGRET
GeV excess which by now is generally interpreted as an instrumental effect. The
contribution from SCRs is predicted to increasingly exceed the DGE models also
above 100 GeV, up to \gr energies of about ten TeV, where the corresponding
surplus exceeds the hadronic part of the DGE by about one order of magnitude.
Above such energies the emission surplus should decrease again with energy due
to the finite life-time of the assumed supernova remnant sources. Observations
of the DGE in the inner Galaxy at 15 TeV with the Milagro \gr detector and, at
TeV energies, with the ARGO-YBJ detector are interpreted to provide
confirmation of a significant SCR contribution to the DGE.Comment: 6 pages, 1 figure. Accepted for publication in The Astrophysical
Journal, 2013; added referenc
New Results from High Energy Gamma-Ray Astronomy
High energy gamma-ray astronomy has recently made significant progresss
through ground-based instruments like the {\it H.E.S.S.} array of imaging
atmospheric Cherenkov telescopes. The unprecedented angular resolution and the
large field of view has allowed to spatially resolve for the first time the
morphology of gamma-ray sources in the TeV energy range. The experimental
technique is described and the types of sources detected and still expected are
discussed. Selected results include objects as different as a Galactic binary
Pulsar, the Galactic Center and Supernova Remnants but they also concern the
diffuse extragalactic optical/infrared radiation field. Finally, a scan of the
Galactic plane in TeV gamma rays is described which has led to a significant
number of new TeV sources, many of which are still unidentified in other
wavelengths. The field has a close connection with X-ray astronomy which allows
the study of the synchrotron emission from these very high energy sources.Comment: 10 pages, 6 figures, Invited paper at IAU Symposium No.230, 2005, in
Dublin (Ireland); E.J.A. Meurs, G. Fabbiano, eds.; in press (2006
Imaging Very High Energy Gamma-Ray Telescopes
The technique of gamma-ray astronomy at very high energies (VHE: > 100 GeV)
with ground-based imaging atmospheric Cherenkov telescopes is described, the
H.E.S.S. array in Namibia serving as example. Mainly a discussion of the
physical principles of the atmospheric Cherenkov technique is given,
emphasizing its rapid development during the last decade. The present status is
illustrated by two examples: the spectral and morphological characterization in
VHE gamma-rays of a shell-type supernova remnant together with its theoretical
interpretation, and the results of a survey of the Galactic Plane that shows a
large variety of non-thermal sources. The final part is devoted to an overview
of the ongoing and future instrumental developments.Comment: To be published in Experimental Astronomy. Also to be published in
proceedings "400 Years of Astronomical Telescopes: A Review of History,
Science and Technology", editors B.R. Brandl, R. Stuik, J.K.
Katgert-Merkelijn, Springer 200