79 research outputs found
TeV GAMMA RAYS: OBSERVATIONS VERSUS EXPECTATIONS & THEORY
The scope of this paper is to discuss two important questions relevant for TeV γ-ray astronomy; the pursuit to reveal the origin of cosmic rays in our galaxy, and the opacity of the universe in γ-rays. The origin of cosmic rays stipulated the field of TeV astronomy in the first place, and led to the development of the atmospheric Cherenkov technique; significant progress has been made in the last decade through the detection of several supernova remnants, the primary suspects for harboring the acceleration sites of cosmic rays. TeV γ-rays propagate mostly unhindered through the galactic plane, making them excellent probes of processes in SNRs and other galactic sources. Key results related to the SNR origin of cosmic rays are discussed. TeV γ-ray spectra from extragalactic sources experience significant absorption when traversing cosmological distances. The opacity of the universe to γ-rays above 10 GeV progressively increases with energy and redshift; the reason lies in their pair production with ambient soft photons from the extragalactic background light (EBL). While this limits the γ-ray horizon, it offers the opportunity to gain information about cosmology, i.e. the EBL intensity, physical conditions in intergalactic space, and potentially new interaction processes. Results and implications pertaining to the EBL are given
A Fast Topological Trigger for Real Time Analysis of Nanosecond Phenomena; Opening the Gamma Ray Window to Our Universe
This work was to enable the development of a proof-of-principle nanosecond trigger system that is designed to perform a real time analysis of fast Cherenkov light flashes from air showers. The basic building blocks of the trigger system have been designed and constructed, and a real world system is now operating in the VERITAS experiment
The Near Infrared Background: Interplanetary Dust or Primordial Stars?
The intensity of the diffuse ~ 1 - 4 micron sky emission from which solar
system and Galactic foregrounds have been subtracted is in excess of that
expected from energy released by galaxies and stars that formed during the z <
5 redshift interval (Arendt & Dwek 2003, Matsumoto et al. 2005). The spectral
signature of this excess near-infrared background light (NIRBL) component is
almost identical to that of reflected sunlight from the interplanetary dust
cloud, and could therefore be the result of the incomplete subtraction of this
foreground emission component from the diffuse sky maps. Alternatively, this
emission component could be extragalactic. Its spectral signature is consistent
with that of redshifted continuum and recombination line emission from HII
regions formed by the first generation of very massive stars. In this paper we
analyze the implications of this spectral component for the formation rate of
these Population III stars, the redshift interval during which they formed, the
reionization of the universe and evolution of collapsed halo masses. We find
that to reproduce the intensity and spectral shape of the NIRBL requires a peak
star formation rate that is higher by about a factor of 4 to 10 compared to
those derived from hierarchical models. Furthermore, an extragalactic origin
for the NIRBL leads to physically unrealistic absorption-corrected spectra of
distant TeV blazars. All these results suggest that Pop III stars contribute
only a fraction of the NIRBL intensity with zodiacal light, star forming
galaxies, and/or non-nuclear sources giving rise to the remaining fraction.Comment: 28 pages including 7 embedded figures. Submitted to Ap
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