Synchrotron emission pervades the Galactic plane at low radio frequencies, originating from cosmic ray electrons interacting with the Galactic magnetic field. Using a low-frequency radio telescope, ...the Murchison Widefield Array (MWA), we measure the free-free absorption of this Galactic synchrotron emission by intervening H ii regions along the line of sight. These absorption measurements allow us to calculate the Galactic cosmic ray electron emissivity behind and in front of 47 detected H ii regions in the region 250... < l < 355..., |b| < 2°. We find that all average emissivities between the H ii regions and the Galactic edge along the line of sight (eb) are in the range of 0.39 ~ 1.45 K pc-1 with a mean of 0.77 K pc-1 and a variance of 0.14 K pc-1 at 88 MHz. Our best model, the two-circle model, divides the Galactic disc into three regions using two circles centring on the Galactic Centre. It shows a high emissivity region near the Galactic Centre, a low emissivity region near the Galactic edge, and a medium emissivity region between these two regions, contrary to the trend found by previous studies. (ProQuest: ... denotes formulae/symbols omitted.)
In this paper we explore the possibility that the MWA can be used for the purposes of Space Situational Awareness (SSA). In particular we propose that the MWA can be used as an element of a passive ...radar facility operating in the frequency range 87.5-108 MHz (the commercial FM broadcast band). The imaging capabilities of the MWA can be used to simultaneously detect multiple pieces of space debris, image their positions on the sky as a function of time, and provide tracking data that can be used to determine orbital parameters. We provide a feasibility assessment of this proposal, based on simple calculations and electromagnetic simulations, that shows that the detection of sub-meter size debris should be possible (debris radius of > 0.5 m to ~ 1000 km altitude).
Critical Tales Lyons, John D; McKinley, Mary B
11/2016
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Provocative and wide-ranging, appealing to specialists in numerous fields, Critical Tales is the first collective volume of studies in English on the Heptameron.
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