634 research outputs found
Constraints on the Cosmic Infra-Red Background based on BeppoSAX and CAT spectra of Mkn 501
The TeV and X-ray data obtained by the imaging Cherenkov telescope CAT and X-ray satellite BeppoSAX during the remarkable flare of Mkn 501 in April 16, 1997 are used to constrain the flux of the Cosmic Infrared Background (CIB) using different CIB models. We show that a non-negligible absorption of gamma-rays due to the CIB could take place already in the low-energy (sub-TeV) domain of the spectrum of Mkn 501. This implies that the data of the low-energy threshold CAT telescope contain very important information about the CIB at short wavelengths, 0.4 mum <= lambda <= 3. mum. The analysis of almost simultaneous spectroscopic measurements of Mkn 501 in a high state by CAT and BeppoSAX in the framework of the standard homogeneous Synchrotron-Self-Compton (SSC) framework model leads to the conclusion that the density of the near-infrared background with typical ``starlight spectrum'' around 1 mum should be between 5 and 35 nW m^-2 sr^-1 (99 % CL), with most likely value around 20 nW m^-2 sr^-1. Also we argue that the CAT gamma-ray data alone allow rather robust upper limits on the CIB, lambda F_lambda <= 60 nW m^-2 sr^-1 at 1 mum, taking into account that for any reasonable scenario of gamma-ray production the differential intrinsic spectrum of gamma-ray hardly could be flatter than dN/dE == E^-1. This estimate agrees, within statistical and systematic uncertainties, with recent reports about tentative detections of the CIB at 2.2 and 3.5 mum by the Diffuse Infrared Background Experiment (DIRBE), as well as with the measurements of the background radiation at optical wavelengths from absolute photometry. We also discuss the impact of the intergalactic absorption effect in derivation of the SSC parameters for the jet in Mkn 501
Comparison of simulated longitudinal profiles of hadronic air showers with MASS2 balloon data
The KASKADE and CORSIKA air shower generators are compared to the data
collected by MASS2 balloon experiment in 1991. The test of longitudinal profile
for proton, helium and muon flux production provide good constraints on these
air shower generators. KASKADE and CORSIKA especially with the new simulator
UrQMD for low energies are found to fit these data well. This study is limited
to a comparison of longitudinal profiles and therefore does not provide
constraints on the overall shower development.Comment: to be published in Astroparticle Physic
Spectrum and Variability of Mrk501 as observed by the CAT Imaging Telescope
The CAT Imaging Telescope has observed the BL Lac object Markarian 501
between March and August 1997. We report here on the variability over this time
including several large flares. We present also preliminary spectra for all
these data, for the low emission state, and for the largest flare.Comment: 4 pages, 4 figures, Late
The camera of the fifth H.E.S.S. telescope. Part I: System description
In July 2012, as the four ground-based gamma-ray telescopes of the H.E.S.S.
(High Energy Stereoscopic System) array reached their tenth year of operation
in Khomas Highlands, Namibia, a fifth telescope took its first data as part of
the system. This new Cherenkov detector, comprising a 614.5 m^2 reflector with
a highly pixelized camera in its focal plane, improves the sensitivity of the
current array by a factor two and extends its energy domain down to a few tens
of GeV.
The present part I of the paper gives a detailed description of the fifth
H.E.S.S. telescope's camera, presenting the details of both the hardware and
the software, emphasizing the main improvements as compared to previous
H.E.S.S. camera technology.Comment: 16 pages, 13 figures, accepted for publication in NIM
Observation of the Crab Nebula Gamma-Ray Emission Above 220 Gev by the Cat Cherenkov Imaging Telescope
The CAT imaging telescope, recently built on the site of the former solar
plant Themis (French Pyrenees), observed gamma-rays from the Crab nebula from
October 1996 to March 1997. This steady source, often considered as the
standard candle of very-high-energy gamma-ray astronomy, is used as a test-beam
to probe the performances of the new telescope, particularly its energy
threshold (220 GeV at 20 degrees zenith angle) and the stability of its
response. Due to the fine-grain camera, an accurate analysis of the
longitudinal profiles of shower images is performed, yielding the source
position in two dimensions for each individual shower.Comment: 5 pages, 3 figures, Tex, contribution to 25th ICRC Durba
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