66 research outputs found
Locating very high energy gamma ray sources with arc minute accuracy
The angular accuracy of gamma-ray detectors is intrinsically limited by the physical processes involved in photon detection. Although a number of point-like sources were detected by the COS-B satellite, only two were unambiguously identified by time signature with counterparts at longer wavelengths. By taking advantage of the extended longitudinal structure of Very High Energy gamma-ray showers, measurements in the TeV energy range can pinpoint source coordinates to arc minute accuracy. This was demonstrated using Cerenkov air shower imaging techniques. With two telescopes in coincidence, the individual event circular probable error will be 0.13 deg. The half-cone angle of the field of view is effectively 1 deg
The STACEE-32 Ground Based Gamma-ray Detector
We describe the design and performance of the Solar Tower Atmospheric
Cherenkov Effect Experiment detector in its initial configuration (STACEE-32).
STACEE is a new ground-based gamma ray detector using the atmospheric Cherenkov
technique. In STACEE, the heliostats of a solar energy research array are used
to collect and focus the Cherenkov photons produced in gamma-ray induced air
showers. The large Cherenkov photon collection area of STACEE results in a
gamma-ray energy threshold below that of previous detectors.Comment: 45 pages, 25 figures, Accepted for publication in Nuclear Instruments
and Methods
Very High Energy Gamma-Ray Emission from the Blazar Markarian 421
Very high energy gamma-ray emission from the BL Lac object Markarian 421 has
been detected over three observing seasons on 59 nights between April 1992 and
June 1994 with the Whipple 10-meter imaging Cherenkov telescope. During its
initial detection in 1992, its flux above 500 GeV was
1.610photons cm s. Observations in 1993 confirmed
this level of emission. For observations made between December 1993 and April
1994, its intensity was a factor of 2.20.5 lower. Observations on 14 and
15 May, 1994 showed an increase over this quiescent level by a factor of
10 (Kerrick et al. 1995). This strong outburst suggests that 4 episodes
of increased flux measurements on similar time scales in 1992 and 1994 may be
attributed to somewhat weaker outbursts. The variability of the TeV gamma-ray
emission from Markarian 421 stands in contrast to EGRET observations (Lin et
al. 1994) which show no evidence for variability.Comment: gzip compressed tar file including LaTeX text and 4 postscript
figures (14 pages total incl. 4 tables), accepted for publication in the
Astrophysical Journal. Contact address is [email protected]
A New Measurement of Cosmic Ray Composition at the Knee
The Dual Imaging Cerenkov Experiment (DICE) was designed and operated for
making elemental composition measurements of cosmic rays near the knee of the
spectrum at several PeV. Here we present the first results using this
experiment from the measurement of the average location of the depth of shower
maximum, , in the atmosphere as a function of particle energy. The value
of near the instrument threshold of ~0.1 PeV is consistent with
expectations from previous direct measurements. At higher energies there is
little change in composition up to ~5 PeV. Above this energy is deeper
than expected for a constant elemental composition implying the overall
elemental composition is becoming lighter above the knee region. These results
disagree with the idea that cosmic rays should become on average heavier above
the knee. Instead they suggest a transition to a qualitatively different
population of particles above 5 PeV.Comment: 7 pages, LaTeX, two eps figures, aas2pp4.sty and epsf.sty included,
accepted by Ap.J. Let
Constraints on Gamma-ray Emission from the Galactic Plane at 300 TeV
We describe a new search for diffuse ultrahigh energy gamma-ray emission
associated with molecular clouds in the galactic disk. The Chicago Air Shower
Array (CASA), operating in coincidence with the Michigan muon array (MIA), has
recorded over 2.2 x 10^{9} air showers from April 4, 1990 to October 7, 1995.
We search for gamma rays based upon the muon content of air showers arriving
from the direction of the galactic plane. We find no significant evidence for
diffuse gamma-ray emission, and we set an upper limit on the ratio of gamma
rays to normal hadronic cosmic rays at less than 2.4 x 10^{-5} at 310 TeV (90%
confidence limit) from the galactic plane region: (50 degrees < l < 200
degrees); -5 degrees < b < 5 degrees). This limit places a strong constraint on
models for emission from molecular clouds in the galaxy. We rule out
significant spectral hardening in the outer galaxy, and conclude that emission
from the plane at these energies is likely to be dominated by the decay of
neutral pions resulting from cosmic rays interactions with passive target gas
molecules.Comment: Astrophysical Journal, submitted, 11 pages, AASTeX Latex, 3
Postscript figure
Region of Excessive Flux of PeV Cosmic Rays in the Direction Toward Pulsars PSR J1840+5640 and LAT PSR J1836+5925
An analysis of arrival directions of extensive air showers (EAS) registered
with the EAS MSU and EAS-1000 prototype arrays has revealed a region of
excessive flux of PeV cosmic rays in the direction toward pulsars PSR
J1840+5640 and LAT PSR J1836+5925 at significance level up to 4.5sigma. The
first of the pulsars was discovered almost 30 years ago and is a well-studied
old radio pulsar located at the distance of 1.7pc from the Solar system. The
second pulsar belongs to a new type of pulsars, discovered by the space
gamma-ray observatory Fermi, pulsations of which are not observed in optical
and radio wavelengths but only in the gamma-ray range of energies
(gamma-ray-only pulsars). In our opinion, the existence of the region of
excessive flux of cosmic rays registered with two different arrays provides a
strong evidence that isolated pulsars can give a noticeable contribution to the
flux of Galactic cosmic rays in the PeV energy range.Comment: 14 pages; v.2: a few remarks to match a version accepted for
Astronomy Letters added. They can be found by redefining the \NEW command in
the preamble of the LaTeX fil
Visitor spending at wine festivals: Perspectives on stakeholder benefits
Economic benefit is a motivator for communities and wineries to participate in events (Byrd et al., 2016; Kim et al., 2008). Two primary stakeholders have a vested interest in the success of wine festivals: participating wineries and host communities. Tourism is a driver of local wine sales, since most regional wineries are small-scale and lack access to traditional distribution channels. Nonetheless, investment in festivals needs to be evaluated against the reality that events often fail to meet expectations for returns on stakeholder investment (Crompton & Lee, 2000)
Search for Ultra High Energy (UHE) γ-ray counterparts of BATSE 3B catalog events
We search for a Ultra High Energy (E>1014 eV)(E>1014eV) counterpart source to cosmic γ-ray bursts detected with the BATSE detectors. Using the 3B catalog positions, we examine 115 candidate bursts with the CASA-MIA detector for UHE γ-ray emission at or near the time of the observed γ-ray burst. No statistically significant excess of γ-rays is found from any of the candidate event regions. Based upon these results, we calculate the flux limits for UHE emission from these candidate event regions. Typical 95% confidence level flux limits are about 6×10−12 γ  cm−2 sec−16×10−12γcm−2sec−1 at a γ-ray detection threshold of 160 TeV. © 1996 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87368/2/598_1.pd
Observations of the Crab nebula at TeV energies
The results of four years of observation of the Crab Nebula at TeV energies by the Whipple group are discussed and the status of the Crab Nebula as a standard candle for TeV astronomy is reviewed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87647/2/270_1.pd
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