49 research outputs found
Radioastronomical investigations of the small scale spatial inhomogeneities' motions and dimensions
Radioastronomical method for solar wind measurement
Results of Observations of 560 Radio Sources in the Frequency of 86 Megahertz
Flux density measurements of 560 radio sources in 86 megahertz frequenc
IPS Observation System for Miyun 50m Radio Telescope and Its Acceptance Observation
Ground-based observation of Interplanetary Scintillation(IPS) is an important
approach of monitoring solar wind. A ground-based IPS observation system is
newly implemented on 50m radio telescope, Miyun station, National Astronomical
Observatories, Chinese Academy of Sciences(NAOC). This observation system is
constructed for purpose of observing the solar wind speed and scintillation
index by using the normalized cross-spectrum of simultaneous dual-frequency IPS
measurement. The system consists of a universal dual-frequency front-end and a
dual-channel multi-function back-end specially designed for IPS. After careful
calibration and testing, IPS observations on source 3C273B and 3C279 are
successfully carried out. The preliminary observation results show that this
newly developed observation system is capable of doing IPS observation.The
system sensitivity for IPS observation can reach over 0.3Jy in terms of IPS
polarization correlator with 4MHz bandwidth and 2s integration time.Comment: 8 pages, 7 figure
Observation of Interplanetary Scintillation with Single-Station Mode at Urumqi
The Sun affects the Earth's physical phenomena in multiple ways, in
particular the material in interplanetary space comes from coronal expansion in
the form of inhomogeneous plasma flow (solar wind), which is the primary source
of the interplanetary medium. Ground-based Interplanetary Scintillation (IPS)
observations are an important and effective method for measuring solar wind
speed and the structures of small diameter radio sources. We discuss one mode
of ground-based single-station observations: Single-Station Single-Frequency
(SSSF) mode. To realize the SSSF mode, a new system has been established at
Urumqi Astronomical Observatory (UAO), China, and a series of experimental
observations were carried out successfully from May to December, 2008
PSR B0809+74: Understanding Its Perplexing Subpulse-separation (P2) Variations
The longitude separation between adjacent drifting subpulses, , is
roughly constant for many pulsars. It was then perplexing when pulsar B0809+74
was found to exhibit substantial variations in this measure, both with
wavelength and with longitude position within the pulse window. We analyze
these variations between 40 and 1400 MHz, and we show that they stem primarily
from the incoherent superposition of the two orthogonal modes of polarization.Comment: Submitted for publication Astronomy and Astrophysic
Evidence for Cosmic Ray Acceleration in Cassiopeia A
Combining archival data taken at radio and infrared wavelengths with
state-of-the-art measurements at X-ray and gamma-ray energies, we assembled a
broadband spectral energy distribution (SED) of Cas A, a young supernova
remnant. Except for strong thermal emission at infrared and X-ray wavelengths,
the SED is dominated by non-thermal radiation. We attempted to model the
non-thermal SED with a two-zone leptonic model which assumes that the radio
emission is produced by electrons that are uniformly distributed throughout the
remnant while the non-thermal X-ray emission by electrons that are localized in
regions near the forward shock. Synchrotron emission from the electrons can
account for data from radio to X-ray wavelengths. Much of the GeV-TeV emission
can also be explained by a combination of bremsstrahlung emission and
inverse-Compton scattering (mainly of infrared thermal photons). However, the
model cannot fit a distinct feature at GeV energies. This feature can be well
accounted for by adding a pion-zero emission component to the model, providing
evidence for cosmic ray production in Cas A. We discuss the implications of the
results.Comment: 16 pages, 4 figure
Properties of the linearly polarized radiation from PSR B0950+08
Measurements of average pulse profiles made with a single linear polarization
over the range 41-112 MHz are presented for PSR B0950+08. We show that the
observed variable structure of the pulse profiles is a result of Faraday
sinusoidal modulation of the pulse intensity with frequency. The rotation
measure corresponding to this effect, RM = 4 rad/m^2, is about 3 times greater
than the tabulated value of RM = 1.35 rad/m^2.Comment: 18 pages, including 10 figures. Accepted for publication in A&