73 research outputs found
Flux Sensitivity of VERITAS
VERITAS is a new major ground-based gamma-ray observatory with an array of
seven 10 m optical reflectors to be built at the Whipple Observatory in
southern Arizona, USA. It will consist of an array of imaging Cherenkov
telescopes designed to conduct critical measurements of AGNs and SNRs in the
energy range of 50 GeV - 50 TeV. The design of the array has been optimized for
the highest sensitivity to point sources in the 100 GeV - 10 TeV band when the
stereoscopic imaging technique is employed. Maximum versatility of the array
has been another major optimization criterion. We present the flux sensitivity
of the baseline VERITAS configuration.Comment: 5 pages, 1 figure, presented at VERITAS Workshop on TeV Astrophysics
of Extragalactic Sources, Cambridge, MA, Oct. 23-24, 1998. In press,
Astroparticle Physics, ed. M. Catanese, J. Quinn, T. Weeke
On the application of differences in intrinsic fluctuations of Cherenkov light images for separation of air showers
The sensitivity of ground-based imaging atmospheric Cherenkov gamma-ray
observatories depends critically on the primary particle identification methods
which are used to retain photon-initiated events and suppress the spurious
background produced by cosmic rays. We suggest a new discrimination technique
which utilizes differences in the fluctuations of the light intensity in the
images of showers initiated by photons and those initiated by protons or
heavier nuclei. The database of simulated events for the proposed VERITAS
observatory has been used to evaluate the efficiency of the new technique.
Analysis has been performed for both a single VERITAS imaging telescope, and a
system of these telescopes. We demonstrate that a discrimination efficiency of
> 1.5 - 2.0 can be achieved in addition to traditional background rejection
methods based on image shape parameters.Comment: 17 pages, 9 figures, accepted for publucation in Astropart. Phy
Production of Miniature Glass Cells with Rubidium for Chip Scale Atomic Clock
AbstractThe main advantage of chip scale atomic clock (e.g., Knappe (2008)) (CSAC) over quartz-oscillators is the higher long-term stability. It is provided by non-aging resonance of unperturbed atoms. However it is not a simple task to suppress all possible perturbations. Hence, metrological properties of resonance depend on the way in which ensemble of atoms is localized in space and protected. The paper describes a technology of small all-glass Rb cells production. The sealing of cells is made with radiation of a СО2 lasers. The cells will be utilized in Rb CSAC based on the phenomenon of coherent population trapping (CPT). (Pat. No RU 2014101361
VERITAS: the Very Energetic Radiation Imaging Telescope Array System
The Very Energetic Radiation Imaging Telescope Array System (VERITAS)
represents an important step forward in the study of extreme astrophysical
processes in the universe. It combines the power of the atmospheric Cherenkov
imaging technique using a large optical reflector with the power of
stereoscopic observatories using arrays of separated telescopes looking at the
same shower. The seven identical telescopes in VERITAS, each of aperture 10 m,
will be deployed in a filled hexagonal pattern of side 80 m; each telescope
will have a camera consisting of 499 pixels with a field of view of 3.5 deg
VERITAS will substantially increase the catalog of very high energy (E >
100GeV) gamma-ray sources and greatly improve measurements of established
sources.Comment: 44 pages, 16 figure
Extragalactic background light absorption signal in the TeV gamma-ray spectra of blazars
Recent observations of the TeV gamma-ray spectra of the two closest active
galactic nuclei (AGNs), Markarian 501 (Mrk 501) and Markarian 421 (Mrk 421), by
the Whipple and HEGRA collaborations have stimulated efforts to estimate or
limit the spectral energy density (SED) of extragalactic background light (EBL)
which causes attenuation of TeV photons via pair-production when they travel
cosmological distances. In spite of the lack of any distinct cutoff-like
feature in the spectra of Mrk 501 and Mrk 421 (in the interval 0.26-10 TeV)
which could clearly indicate the presence of such a photon absorption
mechanism, we demonstrate that strong EBL attenuation signal (survival
probability of 10 TeV photon <10^{-2}) may still be present in the spectra of
these AGNs. By estimating the minimal and maximal opacity of the universe to
TeV gamma-ray photons, we calculate the visibility range for current and future
gamma-ray observatories. Finally, we show that the proposed experiments,
VERITAS, HESS, and MAGIC, may even be able to actually measure the EBL SED
because their observations extend to the critical 75-150 GeV regime. In this
transition region a distinct ``knee-like'' feature should exist in the spectra
of blazars, which is invariant with respect to their intrinsic properties. The
change of the spectral index and flux amplitude across this knee, if observed
for several blazars, will provide missing pieces of information needed to
measure EBL in the wavelength range 0.1-30 m.Comment: Accepted for publication in Astroparticle Physic
The First VERITAS Telescope
The first atmospheric Cherenkov telescope of VERITAS (the Very Energetic
Radiation Imaging Telescope Array System) has been in operation since February
2005. We present here a technical description of the instrument and a summary
of its performance. The calibration methods are described, along with the
results of Monte Carlo simulations of the telescope and comparisons between
real and simulated data. The analysis of TeV -ray observations of the
Crab Nebula, including the reconstructed energy spectrum, is shown to give
results consistent with earlier measurements. The telescope is operating as
expected and has met or exceeded all design specifications.Comment: Accepted by Astroparticle Physic
Multiwavelength observations of a TeV-Flare from W comae
We report results from an intensive multiwavelength campaign on the intermediate-frequency-peaked BL Lacertae object W Com (z = 0.102) during a strong outburst of very high energy gamma-ray emission in 2008 June. The very high energy gamma-ray signal was detected by VERITAS on 2008 June 7-8 with a flux F(>200 GeV) =(5.7 0.6) × 10-11 cm-2 s -1, about three times brighter than during the discovery of gamma-ray emission from W Com by VERITAS in 2008 March. The initial detection of this flare by VERITAS at energies above 200 GeV was followed by observations in high-energy gamma rays (AGILE; E γ≥ 100 MeV), X-rays (Swift and XMM-Newton), and at UV, and ground-based optical and radio monitoring through the GASP-WEBT consortium and other observatories. Here we describe the multiwavelength data and derive the spectral energy distribution of the source from contemporaneous data taken throughout the flare. © 2009. The American Astronomical Society. All rights reserved
The Great Markarian 421 Flare of 2010 February: Multiwavelength Variability and Correlation Studies
We report on variability and correlation studies using multiwavelength observations of the blazar Mrk 421 during the month of 2010 February, when an extraordinary flare reaching a level of ∼27 Crab Units above 1 TeV was measured in very high energy (VHE) γ-rays with the Very Energetic Radiation Imaging Telescope Array System (VERITAS) observatory. This is the highest flux state for Mrk 421 ever observed in VHE γ-rays. Data are analyzed from a coordinated campaign across multiple instruments, including VHE γ-ray (VERITAS, Major Atmospheric Gamma-ray Imaging Cherenkov), high-energy γ-ray (Fermi-LAT), X-ray (Swift, Rossi X-ray Timing Experiment, MAXI), optical (including the GASP-WEBT collaboration and polarization data), and radio (Metsahovi, Owens Valley Radio Observatory, University of Michigan Radio Astronomy Observatory). Light curves are produced spanning multiple days before and after the peak of the VHE flare, including over several flare "decline" epochs. The main flare statistics allow 2 minute time bins to be constructed in both the VHE and optical bands enabling a cross-correlation analysis that shows evidence for an optical lag of ∼25-55 minutes, the first time-lagged correlation between these bands reported on such short timescales. Limits on the Doppler factor (δ ⪆ 33) and the size of the emission region (δ-1RB≲ 3.8 × 1013cm) are obtained from the fast variability observed by VERITAS during the main flare. Analysis of 10 minute binned VHE and X-ray data over the decline epochs shows an extraordinary range of behavior in the flux-flux relationship, from linear to quadratic to lack of correlation to anticorrelation. Taken together, these detailed observations of an unprecedented flare seen in Mrk 421 are difficult to explain with the classic single-zone synchrotron self-Compton model.</p
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