6,722 research outputs found
The multifrequency Siberian Radioheliograph
The 10-antenna prototype of the multifrequency Siberian radioheliograph is
described. The prototype consists of four parts: antennas with broadband
front-ends, analog back-ends, digital receivers and a correlator. The prototype
antennas are mounted on the outermost stations of the Siberian Solar Radio
Telescope (SSRT) array. A signal from each antenna is transmitted to a workroom
by an analog fiber optical link, laid in an underground tunnel. After mixing,
all signals are digitized and processed by digital receivers before the data
are transmitted to the correlator. The digital receivers and the correlator are
accessible by the LAN. The frequency range of the prototype is from 4 to 8 GHz.
Currently the frequency switching observing mode is used. The prototype data
include both circular polarizations at a number of frequencies given by a list.
This prototype is the first stage of the multifrequency Siberian
radioheliograph development. It is assumed that the radioheliograph will
consist of 96 antennas and will occupy stations of the West-East-South subarray
of the SSRT. The radioheliograph will be fully constructed in autumn of 2012.
We plan to reach the brightness temperature sensitivity about 100 K for the
snapshot image, a spatial resolution up to 13 arcseconds at 8 GHz and
polarization measurement accuracy about a few percent.
First results with the 10-antenna prototype are presented of observations of
solar microwave bursts. The prototype abilities to estimate source size and
locations at different frequencies are discussed
Status Report of the DPHEP Study Group: Towards a Global Effort for Sustainable Data Preservation in High Energy Physics
Data from high-energy physics (HEP) experiments are collected with
significant financial and human effort and are mostly unique. An
inter-experimental study group on HEP data preservation and long-term analysis
was convened as a panel of the International Committee for Future Accelerators
(ICFA). The group was formed by large collider-based experiments and
investigated the technical and organisational aspects of HEP data preservation.
An intermediate report was released in November 2009 addressing the general
issues of data preservation in HEP. This paper includes and extends the
intermediate report. It provides an analysis of the research case for data
preservation and a detailed description of the various projects at experiment,
laboratory and international levels. In addition, the paper provides a concrete
proposal for an international organisation in charge of the data management and
policies in high-energy physics
LOFAR discovery of the fastest-spinning millisecond pulsar in the Galactic field
We report the discovery of PSR J09520607, a 707-Hz binary millisecond
pulsar which is now the fastest-spinning neutron star known in the Galactic
field (i.e., outside of a globular cluster). PSR J09520607 was found using
LOFAR at a central observing frequency of 135 MHz, well below the 300 MHz to 3
GHz frequencies typically used in pulsar searches. The discovery is part of an
ongoing LOFAR survey targeting unassociated Fermi Large Area Telescope
-ray sources. PSR J09520607 is in a 6.42-hr orbit around a very
low-mass companion ( M) and we identify a
strongly variable optical source, modulated at the orbital period of the
pulsar, as the binary companion. The light curve of the companion varies by 1.6
mag from at maximum to , indicating that it is
irradiated by the pulsar wind. Swift observations place a 3- upper
limit on the keV X-ray luminosity of erg
s (using the 0.97 kpc distance inferred from the dispersion measure).
Though no eclipses of the radio pulsar are observed, the properties of the
system classify it as a black widow binary. The radio pulsed spectrum of PSR
J09520607, as determined through flux density measurements at 150 and 350
MHz, is extremely steep with (where ).
We discuss the growing evidence that the fastest-spinning radio pulsars have
exceptionally steep radio spectra, as well as the prospects for finding more
sources like PSR J09520607.Comment: 9 pages, 3 figures, 1 table, published in ApJ letter
ASCR/HEP Exascale Requirements Review Report
This draft report summarizes and details the findings, results, and
recommendations derived from the ASCR/HEP Exascale Requirements Review meeting
held in June, 2015. The main conclusions are as follows. 1) Larger, more
capable computing and data facilities are needed to support HEP science goals
in all three frontiers: Energy, Intensity, and Cosmic. The expected scale of
the demand at the 2025 timescale is at least two orders of magnitude -- and in
some cases greater -- than that available currently. 2) The growth rate of data
produced by simulations is overwhelming the current ability, of both facilities
and researchers, to store and analyze it. Additional resources and new
techniques for data analysis are urgently needed. 3) Data rates and volumes
from HEP experimental facilities are also straining the ability to store and
analyze large and complex data volumes. Appropriately configured
leadership-class facilities can play a transformational role in enabling
scientific discovery from these datasets. 4) A close integration of HPC
simulation and data analysis will aid greatly in interpreting results from HEP
experiments. Such an integration will minimize data movement and facilitate
interdependent workflows. 5) Long-range planning between HEP and ASCR will be
required to meet HEP's research needs. To best use ASCR HPC resources the
experimental HEP program needs a) an established long-term plan for access to
ASCR computational and data resources, b) an ability to map workflows onto HPC
resources, c) the ability for ASCR facilities to accommodate workflows run by
collaborations that can have thousands of individual members, d) to transition
codes to the next-generation HPC platforms that will be available at ASCR
facilities, e) to build up and train a workforce capable of developing and
using simulations and analysis to support HEP scientific research on
next-generation systems.Comment: 77 pages, 13 Figures; draft report, subject to further revisio
KM3NeT: Towards a km3 Mediterranean Neutrino Telescope
The observation of high-energy extraterrestrial neutrinos is one of the most
promising future options to increase our knowledge on non-thermal processes in
the universe. Neutrinos are e.g. unavoidably produced in environments where
high-energy hadrons collide; in particular this almost certainly must be true
in the astrophysical accelerators of cosmic rays, which thus could be
identified unambiguously by sky observations in "neutrino light". To establish
neutrino astronomy beyond the detection of single events, neutrino telescopes
of km3 scale are needed. In order to obtain full sky coverage, a corresponding
detector in the Mediterranean Sea is required to complement the IceCube
experiment currently under construction at the South Pole. The groups pursuing
the current neutrino telescope projects in the Mediterranean Sea, ANTARES, NEMO
and NESTOR, have joined to prepare this future installation in a 3-year,
EU-funded Design Study named KM3NeT. This report will highlight some of the
physics issues to be addressed with the KM3NeT detector and will outline the
path towards its realisation, with a focus on the upcoming Design Study.Comment: Presented at VLVnT2 Workshop, Catania, Siciliy, Italy, 8-11 Nov 200
The structure and emission model of the relativistic jet in the quasar 3C 279 inferred from radio to high-energy gamma-ray observations in 2008-2010
We present time-resolved broad-band observations of the quasar 3C 279
obtained from multi-wavelength campaigns conducted during the first two years
of the Fermi Gamma-ray Space Telescope mission. While investigating the
previously reported gamma-ray/optical flare accompanied by a change in optical
polarization, we found that the optical emission appears delayed with respect
to the gamma-ray emission by about 10 days. X-ray observations reveal a pair of
`isolated' flares separated by ~90 days, with only weak gamma-ray/optical
counterparts. The spectral structure measured by Spitzer reveals a synchrotron
component peaking in the mid-infrared band with a sharp break at the
far-infrared band during the gamma-ray flare, while the peak appears in the
mm/sub-mm band in the low state. Selected spectral energy distributions are
fitted with leptonic models including Comptonization of external radiation
produced in a dusty torus or the broad-line region. Adopting the interpretation
of the polarization swing involving propagation of the emitting region along a
curved trajectory, we can explain the evolution of the broad-band spectra
during the gamma-ray flaring event by a shift of its location from ~ 1 pc to ~
4 pc from the central black hole. On the other hand, if the gamma-ray flare is
generated instead at sub-pc distance from the central black hole, the
far-infrared break can be explained by synchrotron self-absorption. We also
model the low spectral state, dominated by the mm/sub-mm peaking synchrotron
component, and suggest that the corresponding inverse-Compton component
explains the steady X-ray emission.Comment: 23 pages, 18 figures 5 tables, Accepted for publication in The
Astrophysical Journa
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