1,442 research outputs found
Optical depth for VHE gamma-rays from distant sources from a generic EBL density
Very-high-energy (VHE; E>100GeV) gamma-rays from distant sources suffer
attenuation through pair-production with low energy photons from the diffuse
extragalactic photon fields in the ultraviolet (UV) to far-infrared (FIR)
(commonly referred to as Extragalactic Background Light; EBL). When modeling
the intrinsic spectra of the VHE gamma-ray sources it is crucial to correctly
account for the attenuation. Unfortunately, direct measurements of the EBL are
difficult and the knowledge about the EBL over certain wavelength ranges is
poor. To calculate the EBL attenuation usually predictions from theoretical
models are used. Recently, the limits on the EBL from direct and indirect
methods have narrowed down the possible EBL range and many of the previous
models are in conflict with these limits. We propose a new generic EBL density
(not a complete model), which is in compliance with the new EBL limits. EBL
evolution with redshift is included in the calculation in a very simple but
effective ad-hoc way. Properties of this generic EBL are discussed.Comment: Proceedings of the workshop 'High Energy Phenomena in Relativistic
Outflows' (HEPRO), Dublin, 24-28 September 200
K-band high power latching switch
A 19 GHz waveguide latching switch with a bandwidth of 1400 MHz and an exceptionally low insertion loss of 0.25 dB was demonstrated. The RF and driver ferrites are separate structures and can be optimized individually. This analysis for each structure is separately detailed. Basically, the RF section features a dual turnstile junction. The circulator consists of a dielectric tube which contains two ferrite rods, and a dielectric spacer separating the ferrite parts along the center of symmetry of the waveguide to form two turnstiles. This subassembly is indexed and locked in the center of symmetry of a uniform junction of three waveguides by the metallic transformers installed in the top and bottom walls of the housing. The switching junction and its actuating circuitry met all RF performance objectives and all shock and vibration requirements with no physical damage or performance degradation. It exceeds thermal requirements by operating over a 100 C temperature range (-44 C to +56 C) and has a high power handling capability allowing up to 100 W of CW input power
Mutations of the ret protooncogene in German multiple endocrine neoplasia families: Relation between genotype and phenotype.
It has been suggested that not only the position but also the nature of the mutations of the ret protooncogene strongly correlate with the clinical manifestation of the multiple endocrine neoplasm type 2 (MEN 2) syndrome. In particular, individuals with a Cys634-Arg substitution should have a greater risk of developing parathyroid disease. We, therefore, analyzed 94 unrelated families from Germany with inherited medullary thyroid carcinoma (MTC) for mutation of the ret protooncogene. In all but 1 of 59 families with MEN 2A, germline mutations in the extracellular domain of the ret protein were found. Some 81% of the MEN 2A mutations affected codon 634. Phenotype-genotype correlations suggested that the prevalence of pheochromocytoma and hyperparathyroidism is significantly higher in families with codon 634 mutations, but there was no correlation with the nature of the mutation. In all but 1 of 27 familial MTC (FMTC) families, mutations were detected in 1 of 4 cysteines in the extracellular domain of the ret protooncogene. Half of the FMTC mutations affected codon 634. Mutations outside of codon 634 occurred more often in FMTC families than in MEN 2A families. In all but 1 of 8 MEN 2B patients, de novo mutations in codon 918 were found. These data confirm the preferential localization of MEN 2-associated mutations and the correlation between disease phenotype and the position of the ret mutation, but there was no correlation between the occurrence of hyperparathyroidism or pheochromocytoma and the nature of the mutation
The 2010 M 87 VHE flare and its origin: the multi-wavelength picture
The giant radio galaxy M 87, with its proximity (16 Mpc) and its very massive
black hole ((3 - 6) \times 10^9 M_solar), provides a unique laboratory to
investigate very high energy (E>100 GeV; VHE) gamma-ray emission from active
galactic nuclei and, thereby, probe particle acceleration to relativistic
energies near supermassive black holes (SMBH) and in relativistic jets. M 87
has been established as a VHE gamma-ray emitter since 2005. The VHE gamma-ray
emission displays strong variability on timescales as short as a day. In 2008,
a rise in the 43 GHz Very Long Baseline Array (VLBA) radio emission of the
innermost region (core; extension of < 100 Rs ; Schwarzschild radii) was found
to coincide with a flaring activity at VHE. This had been interpreted as a
strong indication that the VHE emission is produced in the direct vicinity of
the SMBH. In 2010 a flare at VHE was again detected triggering further
multi-wavelength (MWL) observations with the VLBA, Chandra, and other
instruments. At the same time, M 87 was also observed with the Fermi-LAT
telescope at MeV/GeV energies, the European VLBI Network (EVN), and the
Liverpool Telescope (LT). Here, preliminary results from the 2010 campaign will
be reported.Comment: 6 pages, 2 figures; Procceedings of the workshop "High Energy
Phenomena in Relativistic Outflows III" (HEPRO III), Barcelona, June 27 -
July 1, 201
The H.E.S.S. extragalactic sky
The H.E.S.S. Cherenkov telescope array, located on the southern hemisphere in
Namibia, studies very high energy (VHE; E>100 GeV) gamma-ray emission from
astrophysical objects. During its successful operations since 2002 more than 80
galactic and extra-galactic gamma-ray sources have been discovered. H.E.S.S.
devotes over 400 hours of observation time per year to the observation of
extra-galactic sources resulting in the discovery of several new sources,
mostly AGNs, and in exciting physics results e.g. the discovery of very rapid
variability during extreme flux outbursts of PKS 2155-304, stringent limits on
the density of the extragalactic background light (EBL) in the near-infrared
derived from the energy spectra of distant sources, or the discovery of
short-term variability in the VHE emission from the radio galaxy M 87. With the
recent launch of the Fermi satellite in 2008 new insights into the physics of
AGNs at GeV energies emerged, leading to the discovery of several new
extragalactic VHE sources. Multi-wavelength observations prove to be a powerful
tool to investigate the production mechanism for VHE emission in AGNs. Here,
new results from H.E.S.S. observations of extragalactic sources will be
presented and their implications for the physics of these sources will be
discussed.Comment: 8 pages, 6 figures, invited review talk, in the proceedings of the
"International Workshop on Beamed and Unbeamed Gamma-Rays from Galaxies"
11-15 April 2011, Lapland Hotel Olos, Muonio, Finland, Journal of Physics:
Conference Series Volume 355, 201
New AGNs discovered by H.E.S.S
During the last year, six new Active Galactic Nuclei (AGN) have been
discovered and studied by H.E.S.S. at Very High Energies (VHE). Some of these
recent discoveries have been made thanks to new enhanced analysis methods and
are presented at this conference for the first time. The three blazars 1ES
0414+009, SHBL J001355.9-185406 and 1RXS J101015.9-311909 have been targeted
for observation due to their high levels of radio and X-ray fluxes, while the
Fermi/LAT catalogue of bright sources triggered the observation of PKS 0447-439
and AP Librae. Additionally, the BL Lac 1ES 1312-423 was discovered in the
field-of-view (FoV) of Centaurus A thanks to the large exposure dedicated by
H.E.S.S. to this particularly interesting source. The newly-discovered sources
are presented here and in three companion presentations at this conference.Comment: 8 pages, 3 figures, proceeding from the 25th Texas Symposium on
Relativistic Astrophysics (Heidelberg, Germany, 2010
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