Astrophysics with High Energy Gamma Rays

Recent results, the present status and the perspectives of high energy gamma-ray astronomy are described. Since the satellite observations by the Compton Gamma Ray Observatory and its precursor missions have been reviewed extensively, emphasis is on the results from the ground-based gamma-ray telescopes. They concern the physics of Pulsar Nebulae, Supernova Remnants in their assumed role as the Galactic sources of Cosmic Rays, Jets from Active Galactic Nuclei, and the Extragalactic Background radiation field due to stars and dust in galaxies. Since the gamma-ray emission is nonthermal, this kind of astronomy deals with the pervasive high-energy nonequilibrium states in the Universe. The present build-up of larger and more sensitive instruments, both on the ground and in space, gives fascinating prospects also for observational cosmology and astroparticle physics. Through realistically possible further observational developments at high mountain altitudes a rapid extension of the field is to be expected.Comment: 23 pages, 11 figures. To appear in "Astronomy, Cosmology and Fundamental Physics", ed. P. A. Shaver, L. Di Lella, and A. Gimenez, Proc. ESA-CERN-ESO Symposium, Garching, March 2002. Springer-Verlag, Berlin, Heidelberg, series "ESO Astrophysics Symposia

Absolute neutrino masses: physics beyond SM, double beta decay and cosmic rays

Absolute neutrino masses provide a key to physics beyond the standard model. We discuss the impact of absolute neutrinos masses on physics beyond the standard model, the experimental possibilities to determine absolute neutrinos masses, and the intriguing connection with the Z-burst model for extreme-energy cosmic rays.Comment: 11 pages, 4 figures. Talk given by H. Paes at the NOON2001 workshop, ICRR, University of Tokyo, Kashiwa, Japan; 2 references update

Propagation of detonations in hydrazine vapor

In the range of greater hydrazine vapor pressure, detonation speed depends exclusively on the extent of the ammonia decomposition in the second reaction stage. As vapor pressure decreases, the ammonia disintegration speed becomes increasingly slower and the reaction reached in the reaction zone increasingly decreases until finally, in the vapor pressure range between 53 and 16 Torr, the contribution of the second stage to detonation propagation disappears, and only the first stage remains active. Since the disintegration speed of the hydrazine in this pressure range has decreased markedly as well, no level, but rather only spinning, detonations occur. Temporary separations of the impact front and the reaction zone in the process lead to fluctuations of the detonation speed

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

Is a Large Intrinsic k_T Needed to Describe Photon + Jet Photoproduction at HERA?

We study the photoproduction of an isolated photon and a jet based on a code of partonic event generator type which includes the full set of next-to-leading order corrections. We compare our results to a recent ZEUS analysis in which an effective k_T of the incoming partons has been determined. We find that no additional intrinsic k_T is needed to describe the data.Comment: 23 pages LaTeX, 12 figure

Isolated prompt photon photoproduction at NLO

We present a full next-to-leading order code to calculate the photoproduction of prompt photons. The code is a general purpose program of partonic event generator type with large flexibility. We study the possibility to constrain the photon structure functions and comment on isolation issues. A comparison to ZEUS data is also shown.Comment: 22 pages LaTeX, 15 figure