High-resolution, high dynamic range VLA images of the M87 jet at 2 centimeters

High Resolution Noise Radar without Fast ADCConventional digital signal processing scheme in noise radars has certain limitations related to combination of high resolution and high dynamic range. The bandwidth of radar signal defines range resolution of any radar: the wider the spectrum the better the resolution. In noise radar with conventional processing the sounding and reference signals are to be digitized at intermediate frequency band and to be processed digitally. The power spectrum bandwidth of noise signal which can be digitized with ADC depends on its sampling rate. In currently available ADCs the faster is sampling rate the smaller is its depth (number of bits). Depth of the ADC determines relation between the smallest and highest observable signals and thus limits its dynamic range. Actually this is the main bottleneck of high resolution Noise Radars: conventional processing does not enable getting high range resolution and high dynamic range at the same time. In the paper we discuss ways to go around this drawback by changing signal processing ideology in noise radar. We present results of our consideration and design of two types of high resolution Noise Radar which uses slow ADCs: noise radar with digital generation of sounding signal and analog evaluation of cross-correlation and stepped frequency noise radar. We describe main ideas of these radar schemes and results of experimental tests of the approaches.

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The radio remnant of Supernova 1987A at high frequencies and high resolution

Proceedings of the International Astronomical Union ◽

10.1017/s1743921313009186 ◽

2013 ◽

Vol 9 (S296) ◽

pp. 23-26

Author(s):

G. Zanardo ◽

L. Staveley-Smith ◽

C. -Y. Ng ◽

B. M. Gaensler ◽

T. M. Potter ◽

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Keyword(s):

High Resolution ◽

Dynamic Range ◽

High Dynamic Range ◽

Radio Image ◽

High Frequencies ◽

Compact Source ◽

Supernova 1987A ◽

New Radio ◽

High Dynamic ◽

Compact Array

AbstractAs the remnant of Supernova (SN) 1987A has been getting brighter over time, new observations at high frequencies have allowed imaging of the radio emission at unprecedented detail. We present a new radio image at 44 GHz of the supernova remnant (SNR), derived from observations performed with the Australia Telescope Compact Array (ATCA) in 2011. The diffraction-limited image has a resolution of 349×225 mas, which is the highest achieved to date in high-dynamic range images of the SNR. We also present a new image at 18 GHz, also derived from ATCA observations performed in 2011, which is super-resolved to 0″.25. The new 44 and 18 GHz images yield the first high-resolution spectral index map of the remnant. The comparison of the 44 GHz image with contemporaneous X-ray and Hα observations allows further investigations of the nature of the remnant asymmetry and sheds more light into the progenitor hypotheses and SN explosion. In light of simple free-free absorption models, we discuss the likelihood of detecting at 44 GHz the possible emission originating from a pulsar wind nebula (PWN) or a compact source in the centre of the remnant.

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