Search

Direct measurements of the extragalactic background light (EBL) in the near-IR to mid-IR waveband are extremely difficult due to an overwhelming foreground from the zodiacal light that outshines the faint cosmological diffuse radiation field by more than an order of magnitude. Indirect constraints on the EBL are provided by γ-ray observations of active galactic nuclei. Using the combination of the Fermi Gamma-Ray Space Telescope together with the current generation of ground-based air Cherenkov telescopes (H.E.S.S., MAGIC, and VERITAS) provides unprecedented sensitivity and spectral coverage for constraining the EBL in the near- to mid-IR. In this paper, we present new limits on the EBL based on the analysis of the broadband spectra of a select set of γ-ray blazars covering 200 MeV to several TeV. The EBL intensity at 15 μm is constrained to be 1.36 ± 0.58 nW m-2 sr-1. We find that the fast evolution and baseline EBL models of Stecker et al., as well as the model of Kneiske et al., predict significantly higher EBL intensities in the mid-IR (15 μm) than is allowed by the constraints derived here. In addition, the model of Franceschini et al. and the fiducial model of Domínguez et al. predict near- to mid-IR ratios smaller than that derived from our analysis. Namely, their intensities in the near-IR are too low while their intensities in the mid-IR are marginally too high. All of the aforementioned models are inconsistent with our analysis at the >3σ level. [ABSTRACT FROM AUTHOR]

Abstract: The VERITAS observatory is an imaging atmospheric Cherenkov telescope array located in southern Arizona and covers an energy range between 100GeV and 30TeV. The VERITAS collaboration pursues a rigorous observing program that targets a range of key science objectives in astrophysics and particle physics; the understanding of the origin of cosmic rays, the search for supersymmetric dark matter self-annihilation, illuminating the connection between black holes and relativistic jets and constraints to the cosmological diffuse infrared background. We provide a summary of results from the first two years of observations with the full 4-telecope array reported at RICAP09. [Copyright &y& Elsevier]

Abstract: The short gamma-ray front air-cherenkov experiment (SGARFACE) uses the Whipple 10m telescope to search for bursts of γ-rays. SGARFACE is sensitive to bursts with duration from a few ns to ∼20μs and with γ-ray energy above 100MeV. SGARFACE began operating in March 2003 and has collected 2.2 million events during an exposure time of 2267h. A search for bursts of γ-rays from explosions of primordial black holes (PBH) was carried out. A Hagedorn-type PBH explosion is predicted to be visible within 60pc of Earth. Background events were caused by cosmic rays and by atmospheric phenomena and their rejection was accomplished to a large extent using the time-resolved images. No unambiguous detection of bursts of γ-rays could be made as the remaining background events mimic the expected shape and time-development of bursts. Upper limits on the PBH explosion rate were derived from the SGARFACE data and are compared to previous and future experiments. We note that a future array of large wide-field air-Cherenkov telescopes equipped with a SGARFACE-like trigger would be able to operate background-free with a 20–30 times higher sensitivity for PBH explosions. [Copyright &y& Elsevier]

The Very Energetic Radiation Imaging Telescope Array System (VERITAS) is the major next generation imaging atmospheric Cherenkov γ-ray telescope in the western hemisphere and will be located in southern Arizona nearby Kitt Peak National Observatory. The VERITAS observatory will provide unprecedented sensitivity to photon energies between 50 GeV and 50 TeV. The first stage is an array of four telescopes to be fully operational in early 2006, with an expansion to seven telescopes envisioned for 2008. The construction of a prototype telescope is underway, for which first light is expected in Fall 2003. The technical concept is outlined and a progress report is given. [Copyright &y& Elsevier]

ABSTRACT The close relation between ground-based TeV observations and satellite borne γ-ray measurements has been important for the understanding of blazars. The observations which involve the TeV component in blazar studies are reviewed. [ABSTRACT FROM AUTHOR]