4,692 research outputs found
High Resolution Rapid Response observations of compact radio sources with the Ceduna Hobart Interferometer (CHI)
Context. Frequent, simultaneous observations across the electromagnetic
spectrum are essential to the study of a range of astrophysical phenomena
including Active Galactic Nuclei. A key tool of such studies is the ability to
observe an object when it flares i.e. exhibits a rapid and significant increase
in its flux density.
Aims. We describe the specific observational procedures and the calibration
techniques that have been developed and tested to create a single baseline
radio interferometer that can rapidly observe a flaring object. This is the
only facility that is dedicated to rapid high resolution radio observations of
an object south of -30 degrees declination. An immediate application is to
provide rapid contemporaneous radio coverage of AGN flaring at {\gamma}-ray
frequencies detected by the Fermi Gamma-ray Space Telescope.
Methods. A single baseline interferometer was formed with radio telescopes in
Hobart, Tasmania and Ceduna, South Australia. A software correlator was set up
at the University of Tasmania to correlate these data.
Results. Measurements of the flux densities of flaring objects can be made
using our observing strategy within half an hour of a triggering event. These
observations can be calibrated with amplitude errors better than 15%. Lower
limits to the brightness temperatures of the sources can also be calculated
using CHI.Comment: 6 pages, 6 figures, 1 table. Accepted for publication in A&
Comparing Wilson and Clover Quenched Spectroscopy with an Improved Gauge Action
We present results of quenched hadron spectroscopy comparing
\order(a) improved Wilson (Clover) fermions with conventional Wilson
fermions. The configurations were generated using an \order(a^2) improved
6-link pure gauge action at 's corresponding to lattice spacings
of , , , , and fm. We find evidence that
fermionic scaling violations are consistent with \order(a^2) for Clover and
\order(a) with a nonnegligible \order(a^2) term for standard Wilson
fermions. This latter mixed ansatz makes a reliable continuum extrapolation
problematic for Wilson fermions. We also find that the slope of the scaling
violations is roughly for both Wilson and Clover fermions.Comment: 3 pages latex with 2 postscript figures. Talk presented at
LATTICE96(spectrum
A novel quark-field creation operator construction for hadronic physics in lattice QCD
A new quark-field smearing algorithm is defined which enables efficient
calculations of a broad range of hadron correlation functions. The technique
applies a low-rank operator to define smooth fields that are to be used in
hadron creation operators. The resulting space of smooth fields is small enough
that all elements of the reduced quark propagator can be computed exactly at
reasonable computational cost. Correlations between arbitrary sources,
including multi hadron operators can be computed a posteriori without requiring
new lattice Dirac operator inversions. The method is tested on realistic
lattice sizes with light dynamical quarks.Comment: 14 pages, 9 figure
Quenched hadron spectroscopy using improved fermionic and gauge actions
We present results of quenched hadron spectroscopy using \order(a)
improved Wilson fermions. The configurations were generated using an
\order(a^2) improved 6-link pure gauge action at 's
corresponding to lattice spacings of , , , , and
fm. We find evidence that fermionic scaling violations are consistent with
\order(a^2) errors.Comment: 4 pages latex with 3 postscript figures. Corrected column heading in
tabl
SCRI Results With the Tadpole-Improved Clover Action
We compare light hadron spectroscopy using the Wilson and Clover fermionic
actions. We show that a Clover coefficient chosen using tadpole-improved
tree-level perturbation theory effectively eliminates the O(a) discretization
errors present in the Wilson action. We find that discretization errors in
light spectroscopy for both the Wilson and Clover actions are characterized by
an energy scale mu of about 200-300 MeV, indicating that these errors can be
reduced to the 5% level by using the Clover action at an inverse lattice
spacing of about 1.3 GeV.Comment: Talk presented at the International Workshop on Lattice QCD On
Parallel Computers, University of Tsukuba, March 10-15 1997. 9 LaTex pages
plus 6 postscript figures, uses espcrc2.st
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