279 research outputs found
Centaurus A at Ultra-High Energies
We review the importance of Centaurus A in high energy astrophysics as a
nearby object with many of the properties expected of a major source of very
high energy cosmic rays and gamma-rays. We examine observational techniques and
the results so far obtained in the energy range from 200 GeV to above 100 EeV
and attempt to fit those data with expectations of Centaurus A as an
astrophysical source from VHE to UHE energies.Comment: 11 pages, 4 figures, accepted for publication in PAS
NIMBUS: The Near-Infrared Multi-Band Ultraprecise Spectroimager for SOFIA
We present a new and innovative near-infrared multi-band ultraprecise
spectroimager (NIMBUS) for SOFIA. This design is capable of characterizing a
large sample of extrasolar planet atmospheres by measuring elemental and
molecular abundances during primary transit and occultation. This wide-field
spectroimager would also provide new insights into Trans-Neptunian Objects
(TNO), Solar System occultations, brown dwarf atmospheres, carbon chemistry in
globular clusters, chemical gradients in nearby galaxies, and galaxy
photometric redshifts. NIMBUS would be the premier ultraprecise spectroimager
by taking advantage of the SOFIA observatory and state of the art infrared
technologies.
This optical design splits the beam into eight separate spectral bandpasses,
centered around key molecular bands from 1 to 4 microns. Each spectral channel
has a wide field of view for simultaneous observations of a reference star that
can decorrelate time-variable atmospheric and optical assembly effects,
allowing the instrument to achieve ultraprecise calibration for imaging and
photometry for a wide variety of astrophysical sources. NIMBUS produces the
same data products as a low-resolution integral field spectrograph over a large
spectral bandpass, but this design obviates many of the problems that preclude
high-precision measurements with traditional slit and integral field
spectrographs. This instrument concept is currently not funded for development.Comment: 14 pages, 9 figures, SPIE Astronomical Telescopes and Instrumentation
201
Search for VHE gamma rays from SS433/W50 with the CANGAROO-II telescope
SS433, located at the center of the supernova remnant W50, is a close proximity binary system consisting of a compact star and a normal star. Jets of material are directed outwards from the vicinity of the compact star symmetrically to the east and west
The global oscillation network group site survey. II. Results
The Global Oscillation Network Group (GONG) Project will place a network of instruments around the world to observe solar oscillations as continuously as possible for three years. The Project has now chosen the six network sites based on analysis of survey data from fifteen sites around the world. The chosen sites are: Big Bear Solar Observatory, California; Mauna Loa Solar Observatory, Hawaii; Learmonth Solar Observatory, Australia; Udaipur Solar Observatory, India; Observatorio del Teide, Tenerife; and Cerro Tololo Interamerican Observatory, Chile.
Total solar intensity at each site yields information on local cloud cover, extinction coefficient, and transparency fluctuations. In addition, the performance of 192 reasonable components analysis. An accompanying paper describes the analysis methods in detail; here we present the results of both the network and individual site analyses.
The selected network has a duty cycle of 93.3%, in good agreement with numerical simulations. The power spectrum of the network observing window shows a first diurnal sidelobe height of 3 Ă 10â»âŽ with respect to the central component, an improvement of a factor of 1300 over a single site. The background level of the network spectrum is lower by a factor of 50 compared to a single-site spectrum
CANGAROO-III Search for Gamma Rays from SN 1987A and the Surrounding Field
Optical images of SN 1987A show a triple ring structure. The inner (dust)
ring has recently increased in brightness and in the number of hot spots
suggesting that the supernova shock wave has collided with the dense
pre-existing circumstellar medium, a scenario supported by radio and X-ray
observations. Such a shocked environment is widely expected to result in the
acceleration of charged particles, and the accompanying emission of very high
energy gamma-rays. Here, we report the results of observations made in 2004 and
2006 which yield upper limits on the TeV gamma-ray flux, which are compared
with a theoretical prediction. In addition, we set upper limits on the TeV flux
for four high energy objects which are located within the same field of view of
the observation: the super-bubble 30 Dor C, the Crab-like pulsar PSR
B054069, the X-ray binary LMC X-1, and the supernova remnant N157B.Comment: 5 pages, 5 figures, Accepted for publication in Ap
Detection of Gamma-rays around 1TeV from RX J0852.0-4622 by CANGAROO-II
We have detected gamma-ray emission at the 6sigma level at energies greater
than 500GeV from the supernova remnant RX J0852.0-4622 (G266.2-1.2) using the
CANGAROO-II Imaging Atmospheric Cherenkov Telescope (IACT). The flux was 0.12
times of that of Crab at 1TeV. The signal centroid is consistent with the peak
of the X-ray emission in the north-west rim of the remnant.Comment: 12pages, 4figures, to be published in ApJ
Induced pseudoscalar coupling of the proton weak interaction
The induced pseudoscalar coupling is the least well known of the weak
coupling constants of the proton's charged--current interaction. Its size is
dictated by chiral symmetry arguments, and its measurement represents an
important test of quantum chromodynamics at low energies. During the past
decade a large body of new data relevant to the coupling has been
accumulated. This data includes measurements of radiative and non radiative
muon capture on targets ranging from hydrogen and few--nucleon systems to
complex nuclei. Herein the authors review the theoretical underpinnings of
, the experimental studies of , and the procedures and uncertainties
in extracting the coupling from data. Current puzzles are highlighted and
future opportunities are discussed.Comment: 58 pages, Latex, Revtex4, prepared for Reviews of Modern Physic
The global oscillation network group site survey. II. Results
The Global Oscillation Network Group (GONG) Project will place a network of instruments around the world to observe solar oscillations as continuously as possible for three years. The Project has now chosen the six network sites based on analysis of survey data from fifteen sites around the world. The chosen sites are: Big Bear Solar Observatory, California; Mauna Loa Solar Observatory, Hawaii; Learmonth Solar Observatory, Australia; Udaipur Solar Observatory, India; Observatorio del Teide, Tenerife; and Cerro Tololo Interamerican Observatory, Chile.
Total solar intensity at each site yields information on local cloud cover, extinction coefficient, and transparency fluctuations. In addition, the performance of 192 reasonable components analysis. An accompanying paper describes the analysis methods in detail; here we present the results of both the network and individual site analyses.
The selected network has a duty cycle of 93.3%, in good agreement with numerical simulations. The power spectrum of the network observing window shows a first diurnal sidelobe height of 3 Ă 10â»âŽ with respect to the central component, an improvement of a factor of 1300 over a single site. The background level of the network spectrum is lower by a factor of 50 compared to a single-site spectrum
Search for Higgs Bosons in e+e- Collisions at 183 GeV
The data collected by the OPAL experiment at sqrts=183 GeV were used to
search for Higgs bosons which are predicted by the Standard Model and various
extensions, such as general models with two Higgs field doublets and the
Minimal Supersymmetric Standard Model (MSSM). The data correspond to an
integrated luminosity of approximately 54pb-1. None of the searches for neutral
and charged Higgs bosons have revealed an excess of events beyond the expected
background. This negative outcome, in combination with similar results from
searches at lower energies, leads to new limits for the Higgs boson masses and
other model parameters. In particular, the 95% confidence level lower limit for
the mass of the Standard Model Higgs boson is 88.3 GeV. Charged Higgs bosons
can be excluded for masses up to 59.5 GeV. In the MSSM, mh > 70.5 GeV and mA >
72.0 GeV are obtained for tan{beta}>1, no and maximal scalar top mixing and
soft SUSY-breaking masses of 1 TeV. The range 0.8 < tanb < 1.9 is excluded for
minimal scalar top mixing and m{top} < 175 GeV. More general scans of the MSSM
parameter space are also considered.Comment: 49 pages. LaTeX, including 33 eps figures, submitted to European
Physical Journal
A Measurement of the Product Branching Ratio f(b->Lambda_b).BR(Lambda_b->Lambda X) in Z0 Decays
The product branching ratio, f(b->Lambda_b).BR(Lambda_b->Lambda X), where
Lambda_b denotes any weakly-decaying b-baryon, has been measured using the OPAL
detector at LEP. Lambda_b are selected by the presence of energetic Lambda
particles in bottom events tagged by the presence of displaced secondary
vertices. A fit to the momenta of the Lambda particles separates signal from B
meson and fragmentation backgrounds. The measured product branching ratio is
f(b->Lambda_b).BR(Lambda_b->Lambda X) = (2.67+-0.38(stat)+0.67-0.60(sys))%
Combined with a previous OPAL measurement, one obtains
f(b->Lambda_b).BR(Lambda_b->Lambda X) = (3.50+-0.32(stat)+-0.35(sys))%.Comment: 16 pages, LaTeX, 3 eps figs included, submitted to the European
Physical Journal
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