204 research outputs found
The Effelsberg-Bonn HI Survey: Data reduction
Starting in winter 2008/2009 an L-band 7-Feed-Array receiver is used for a
21-cm line survey performed with the 100-m telescope, the Effelsberg-Bonn HI
survey (EBHIS). The EBHIS will cover the whole northern hemisphere for decl.>-5
deg comprising both the galactic and extragalactic sky out to a distance of
about 230 Mpc. Using state-of-the-art FPGA-based digital fast Fourier transform
spectrometers, superior in dynamic range and temporal resolution to
conventional correlators, allows us to apply sophisticated radio frequency
interference (RFI) mitigation schemes.
In this paper, the EBHIS data reduction package and first results are
presented. The reduction software consists of RFI detection schemes, flux and
gain-curve calibration, stray-radiation removal, baseline fitting, and finally
the gridding to produce data cubes. The whole software chain is successfully
tested using multi-feed data toward many smaller test fields (1--100 square
degrees) and recently applied for the first time to data of two large sky
areas, each covering about 2000 square degrees. The first large area is toward
the northern galactic pole and the second one toward the northern tip of the
Magellanic Leading Arm. Here, we demonstrate the data quality of EBHIS Milky
Way data and give a first impression on the first data release in 2011.Comment: 17 pages, 14 figures; to be published in ApJ
The Global Magneto-Ionic Medium Survey: Polarimetry of the Southern Sky from 300 to 480 MHz
Much data on the Galactic polarized radio emission has been gathered in the
last five decades. All-sky surveys have been made, but only in narrow, widely
spaced frequency bands, and the data are inadequate for the characterization of
Faraday rotation, the main determinant of the appearance of the polarized radio
sky at decimetre wavelengths. We describe a survey of the polarized radio
emission from the Southern sky, aiming to characterize the magneto-ionic
medium, particularly the strength and configuration of the magnetic field. This
work is part of the Global Magneto-Ionic Medium Survey (GMIMS). We have
designed and built a feed and receiver covering the band 300 to 900 MHz for the
CSIRO Parkes 64-m Telescope. We have surveyed the entire sky between
declinations -90 and +20 degrees. We present data covering 300 to 480 MHz with
angular resolution 81' to 45'. The survey intensity scale is absolutely
calibrated, based on measurements of resistors at known temperatures and on an
assumed flux density and spectral index for Taurus A. Data are presented as
brightness temperatures. We have applied Rotation Measure Synthesis to the data
to obtain a Faraday depth cube of resolution 5.9 radians per metre squared,
sensitivity of 60 mK of polarized intensity, and angular resolution 1.35
degrees. The data presented in this paper are available at the Canadian
Astronomy Data Centre.Comment: Accepted for publication in the Astronomical Journal Modified 29th
June 2019 to replace outdated doi: for access to dat
An ultra-wide bandwidth (704 to 4 032 MHz) receiver for the Parkes radio telescope
We describe an ultra-wide-bandwidth, low-frequency receiver recently installed on the Parkes radio telescope. The receiver system provides continuous frequency coverage from 704 to 4032 MHz. For much of the band ( ), the system temperature is approximately 22 K and the receiver system remains in a linear regime even in the presence of strong mobile phone transmissions. We discuss the scientific and technical aspects of the new receiver, including its astronomical objectives, as well as the feed, receiver, digitiser, and signal processor design. We describe the pipeline routines that form the archive-ready data products and how those data files can be accessed from the archives. The system performance is quantified, including the system noise and linearity, beam shape, antenna efficiency, polarisation calibration, and timing stability
An International Survey of Front-End Receivers and Observing Performance of Telescopes for Radio Astronomy
This paper presents a survey of microwave front-end receivers installed at
radio telescopes throughout the World. This unprecedented analysis was
conducted as part of a review of front-end developments for Italian radio
telescopes, initiated by the Italian National Institute for Astrophysics in
2016. Fifteen international radio telescopes have been selected to be
representative of the instrumentation used for radio astronomical observations
in the frequency domain from 300 MHz to 116 GHz. A comprehensive description of
the existing receivers is presented and their characteristics are compared and
discussed. The observing performances of the complete receiving chains are also
presented. An overview of on-going developments illustrates and anticipates
future trends in front-end projects to meet the most ambitious scientific
research goals.Comment: 34 pages, 13 figures, accepted to PAS
Limits on Absorption from a 332-MHz survey for Fast Radio Bursts
Fast Radio Bursts (FRBs) are bright, extragalactic radio pulses whose origins
are still unknown. Until recently, most FRBs have been detected at frequencies
greater than 1 GHz with a few exceptions at 800 MHz. The recent discoveries of
FRBs at 400 MHz from the Canadian Hydrogen Intensity Mapping Experiment (CHIME)
telescope has opened up possibilities for new insights about the progenitors
while many other low frequency surveys in the past have failed to find any
FRBs. Here, we present results from a FRB survey recently conducted at the
Jodrell Bank Observatory at 332 MHz with the 76-m Lovell telescope for a total
of 58 days. We did not detect any FRBs in the survey and report a 90 upper
limit of 5500 FRBs per day per sky for a Euclidean Universe above a fluence
threshold of 46 Jy ms. We discuss the possibility of absorption as the main
cause of non-detections in low frequency (< 800 MHz) searches and invoke
different absorption models to explain the same. We find that Induced Compton
Scattering alone cannot account for absorption of radio emission and that our
simulations favour a combination of Induced Compton Scattering and Free-Free
Absorption to explain the non-detections. For a free-free absorption scenario,
our constraints on the electron density are consistent with those expected in
the post-shock region of the ionized ejecta in Super-Luminous SuperNovae
(SLSNe).Comment: 12 pages, 9 Figures, 2 Tables, Second revision submitted to MNRA
Architecture and Information Requirements to Assess and Predict Flight Safety Risks During Highly Autonomous Urban Flight Operations
As aviation adopts new and increasingly complex operational paradigms, vehicle types, and technologies to broaden airspace capability and efficiency, maintaining a safe system will require recognition and timely mitigation of new safety issues as they emerge and before significant consequences occur. A shift toward a more predictive risk mitigation capability becomes critical to meet this challenge. In-time safety assurance comprises monitoring, assessment, and mitigation functions that proactively reduce risk in complex operational environments where the interplay of hazards may not be known (and therefore not accounted for) during design. These functions can also help to understand and predict emergent effects caused by the increased use of automation or autonomous functions that may exhibit unexpected non-deterministic behaviors. The envisioned monitoring and assessment functions can look for precursors, anomalies, and trends (PATs) by applying model-based and data-driven methods. Outputs would then drive downstream mitigation(s) if needed to reduce risk. These mitigations may be accomplished using traditional design revision processes or via operational (and sometimes automated) mechanisms. The latter refers to the in-time aspect of the system concept. This report comprises architecture and information requirements and considerations toward enabling such a capability within the domain of low altitude highly autonomous urban flight operations. This domain may span, for example, public-use surveillance missions flown by small unmanned aircraft (e.g., infrastructure inspection, facility management, emergency response, law enforcement, and/or security) to transportation missions flown by larger aircraft that may carry passengers or deliver products. Caveat: Any stated requirements in this report should be considered initial requirements that are intended to drive research and development (R&D). These initial requirements are likely to evolve based on R&D findings, refinement of operational concepts, industry advances, and new industry or regulatory policies or standards related to safety assurance
Multi-frequency measurements of the NVSS foreground sources in the Cosmic Background Imager fields. I. Data release
We present the results of the flux density measurements at 4.85 GHz and 10.45
GHz of a sample of 5998 NVSS radio sources with the Effelsberg 100 m telescope.
The initial motivation was the need to identify the NVSS radio sources that
could potentially contribute significant contaminating flux in the frequency
range at which the Cosmic Background Imager experiment operated. An efficient
way to achieve this challenging goal has been to compute the high frequency
flux density of those sources by extrapolating their radio spectrum. This is
determined by the three-point spectral index measured on the basis of the NVSS
entry at 1.4 GHz and the measurements at 4.85 GHz and 10.45 GHz carried out
with the 100 m Effelsberg telescope. These measurements are important since the
targeted sample probes the weak part of the flux density distribution, hence
the decision to make the data available. We present the table with flux density
measurements of 3434 sources that showed no confusion allowing reliable
measurements, their detection rates, their spectral index distribution and an
interpretation which explains satisfactorily the observed uncertainties.Comment: 13 pages, 9 figures, in pres
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