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Interactions among intermediate redshift galaxies. The case of SDSSJ134420.86+663717.8

ArXiv 2005.12888 (2020)

Authors:

Persis Misquitta, Micah Bowles, Andreas Eckart, Madeleine Yttergren, Gerold Busch, Monica Valencia-S, Nastaran Fazeli
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Plasma density gradients at the edge of polar ionospheric holes: the absence of phase scintillation

Annales Geophysicae Copernicus GmbH 38:2 (2020) 575-590

Authors:

Luke A Jenner, Alan G Wood, Gareth D Dorrian, Kjellmar Oksavik, Timothy K Yeoman, Alexandra R Fogg, Anthea J Coster

Abstract:

Abstract. Polar holes were observed in the high-latitude ionosphere during a series of multi-instrument case studies close to the Northern Hemisphere winter solstice in 2014 and 2015. These holes were observed during geomagnetically quiet conditions and under a range of solar activities using the European Incoherent Scatter (EISCAT) Svalbard Radar (ESR) and measurements from Global Navigation Satellite System (GNSS) receivers. Steep electron density gradients have been associated with phase scintillation in previous studies; however, no enhanced scintillation was detected within the electron density gradients at these boundaries. It is suggested that the lack of phase scintillation may be due to low plasma density levels and a lack of intense particle precipitation. It is concluded that both significant electron density gradients and plasma density levels above a certain threshold are required for scintillation to occur.
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An unusual observation of a plasma structure in the mid-latitude ionosphere

(2020)

Authors:

Alan Wood, Gareth Dorrian, Richard Fallows

Abstract:

<p>The LOFAR (Low Frequency Array) is one of the world’s leading radio telescopes, operating across the frequency band 10-250 MHz. As radio waves from astronomical sources pass through the ionosphere, they can undergo refraction and/or diffraction. The variations in the intensity of the received signal are caused by irregularities with a spatial scale size ranging from the Fresnel dimension to an order of magnitude below this value. The received signal can therefore be used to infer information on plasma structures in the ionosphere. As the frequencies used are significantly lower than the 1.4 GHz typically associated with Global Navigation Satellite Systems (GNSS), the plasma structures that affect the signals received by LOFAR are significantly larger, typically of the order of kilometres.</p><p>On 14<sup>th</sup> July 2018 the Dutch stations of LOFAR observed the strong natural radio sources Cassiopeia A and Cygnus A between 17:00 UT and 18:05 UT at a frequency range of 20-80 MHz. During the observation, the signal intensity received by many of the stations underwent a substantial reduction across all frequencies, lasting approximately 10 minutes. Immediately before and after this, periodic enhancements in the signal strength were observed. These enhancements showed a noticeable frequency dependence, with longer period oscillations at lower frequencies. The feature was not observed simultaneously by the stations and evolved during the observations. Such a feature is most likely to be the result of a large-scale density structure in the ionosphere, which appears to move west and north over the northern Netherlands.</p><p>The deep fading of the received signal may be due to the presence of sporadic-E, which is a consequence of variations in the neutral wind speed with altitude in the presence of the geomagnetic field, resulting in plasma accumulating in a thin layer. This can cause incident radio waves to be strongly refracted, affecting the strength of the received signal. The wave-like structure immediately before and after the deep fade is a likely consequence of scattering of the observed signal.</p>
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Break up of a polar cap patch in the nightside ionosphere due to a flow channel event

(2020)

Authors:

Elizabeth Donegan-Lawley, Alan Wood, Gareth Dorrian, Alexandra Fogg, Timothy Yeoman, Sean Elvidge

Abstract:

<p>Flow channel events have previously been observed breaking up polar cap patches on the dayside ionosphere but, to the best of our knowledge, have not been observed on the nightside. We report observations of a flow channel event in the evening of the 9th January 2019 under quiet geomagnetic conditions. This multi-instrument study was undertaken using a combination of multiple EISCAT (European Incoherent Scatter) radars, SuperDARN (Super Dual Auroral Radar Network), MSP (Meridian Scanning Photometer) and GNSS (Global Navigation Satellite System) scintillation data. These data were used to build a picture of the evening’s observations from 1800 to 2359 UT. The flow channel event lasted a total of 13 minutes and was responsible for segmenting a polar cap patch. A decrease in electron density was observed, from a patch value of 1.4x10<sup>11</sup> m<sup>3</sup> to a minimum value of 5x10<sup>10</sup> m<sup>3</sup>. In addition, ion velocities in excess of 1000 ms<sup>-1</sup> and ion temperatures of greater than 2000 K were also observed. </p>
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An extremely powerful long-lived superluminal ejection from the black hole MAXI J1820+070

(2020)

Authors:

JS Bright, RP Fender, SE Motta, DRA Williams, J Moldon, RM Plotkin, JCA Miller-Jones, I Heywood, E Tremou, R Beswick, GR Sivakoff, S Corbel, DAH Buckley, J Homan, E Gallo, AJ Tetarenko, TD Russell, DA Green, D Titterington, PA Woudt, RP Armstrong, PJ Groot, A Horesh, AJ van der Horst, EG Körding, VA McBride, A Rowlinson, RAMJ Wijers
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