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Papers by Leonid B
Proceedings of RFI mitigation workshop — PoS(RFI2010), 2010
It is shown that the excellent Murchison Radio-astronomy Observatory site allows the Murchison Wi... more It is shown that the excellent Murchison Radio-astronomy Observatory site allows the Murchison Widefield Array to employ a simple RFI blanking scheme and still calibrate visibilities and form images in the FM radio band. The techniques described are running autonomously in our calibration and imaging software, which is currently being used to process an FM-band survey of the entire southern sky. RFI mitigation workshop 29-31 March 2010 Groningen, the Netherlands * Speaker. † This work uses data obtained from the Murchison Radio-astronomy Observatory. We acknowledge the Wajarri Yamatji people as the traditional owners of the Observatory site.
Geophysical Research Letters, 2002
New magnetic parameters, dAE and dAO, are introduced to determine the preferential times for subs... more New magnetic parameters, dAE and dAO, are introduced to determine the preferential times for substorm onsets. dAE and dAO are time derivatives of the standard AE and AO indices. By analyzing long series of dAE and dAO we reveal their seasonal and diurnal variations, which, unlike those of the original AE and AO, show reasonable similarity. The preferential periods of substorm onsets are shifted from the spring and fall equinoxes; they occur around 0900-1800 UT for the winter months with maxima of occurrence in October-November and February-March. Substorms are rarer during summer months at all UT hours, which is in agreement with the results of Newell et al. [1996] that aurora are suppressed in sunlight. The substorm suppression during summer months corresponding to large total conductance of conjugate ionospheres is consistent with one of the potential substorm triggering mechanisms, the magnetosphere-ionosphere feedback instability.
In this thesis, the relationship between several high-latitude phenomena and the ionospheric cond... more In this thesis, the relationship between several high-latitude phenomena and the ionospheric conductance in both hemispheres is studied theoretically and experimentally. Theoretically, the high-latitude electrodynamics is studied by considering currents in the magnetosphere-ionosphere system resulting from the ionospheric sheet current redistribution between the conjugate ionospheres. It is shown that strong flow between the conjugate ionospheres, the interhemispheric currents (IHC), can
arXiv: Instrumentation and Methods for Astrophysics, 2016
General Relativity predicts that the emission close to a black hole must be lensed by its strong ... more General Relativity predicts that the emission close to a black hole must be lensed by its strong gravitational field, illuminating the last photon orbit. This results in a dark circular area known as the black hole 'shadow'. The Event Horizon Telescope (EHT) is a (sub)mm VLBI network capable of Schwarzschild-radius resolution on Sagittarius A* (or Sgr A*), the 4 million solar mass black hole at the Galactic Center. The goals of the Sgr A* observations include resolving and measuring the details of its morphology. However, EHT data are sparse in the visibility domain, complicating reliable detailed image reconstruction. Therefore, direct pixel imaging should be complemented by other approaches. Using simulated EHT data from a black hole emission model we consider an approach to Sgr A* image reconstruction based on a simple and computationally efficient analytical model that produces images similar to the synthetic ones. The model consists of an eccentric ring with a brightnes...
Proceedings of RFI mitigation workshop — PoS(RFI2010), 2010
It is shown that the excellent Murchison Radio-astronomy Observatory site allows the Murchison Wi... more It is shown that the excellent Murchison Radio-astronomy Observatory site allows the Murchison Widefield Array to employ a simple RFI blanking scheme and still calibrate visibilities and form images in the FM radio band. The techniques described are running autonomously in our calibration and imaging software, which is currently being used to process an FM-band survey of the entire southern sky. RFI mitigation workshop 29-31 March 2010 Groningen, the Netherlands * Speaker. † This work uses data obtained from the Murchison Radio-astronomy Observatory. We acknowledge the Wajarri Yamatji people as the traditional owners of the Observatory site.
Geophysical Research Letters, 2002
New magnetic parameters, dAE and dAO, are introduced to determine the preferential times for subs... more New magnetic parameters, dAE and dAO, are introduced to determine the preferential times for substorm onsets. dAE and dAO are time derivatives of the standard AE and AO indices. By analyzing long series of dAE and dAO we reveal their seasonal and diurnal variations, which, unlike those of the original AE and AO, show reasonable similarity. The preferential periods of substorm onsets are shifted from the spring and fall equinoxes; they occur around 0900-1800 UT for the winter months with maxima of occurrence in October-November and February-March. Substorms are rarer during summer months at all UT hours, which is in agreement with the results of Newell et al. [1996] that aurora are suppressed in sunlight. The substorm suppression during summer months corresponding to large total conductance of conjugate ionospheres is consistent with one of the potential substorm triggering mechanisms, the magnetosphere-ionosphere feedback instability.
In this thesis, the relationship between several high-latitude phenomena and the ionospheric cond... more In this thesis, the relationship between several high-latitude phenomena and the ionospheric conductance in both hemispheres is studied theoretically and experimentally. Theoretically, the high-latitude electrodynamics is studied by considering currents in the magnetosphere-ionosphere system resulting from the ionospheric sheet current redistribution between the conjugate ionospheres. It is shown that strong flow between the conjugate ionospheres, the interhemispheric currents (IHC), can
arXiv: Instrumentation and Methods for Astrophysics, 2016
General Relativity predicts that the emission close to a black hole must be lensed by its strong ... more General Relativity predicts that the emission close to a black hole must be lensed by its strong gravitational field, illuminating the last photon orbit. This results in a dark circular area known as the black hole 'shadow'. The Event Horizon Telescope (EHT) is a (sub)mm VLBI network capable of Schwarzschild-radius resolution on Sagittarius A* (or Sgr A*), the 4 million solar mass black hole at the Galactic Center. The goals of the Sgr A* observations include resolving and measuring the details of its morphology. However, EHT data are sparse in the visibility domain, complicating reliable detailed image reconstruction. Therefore, direct pixel imaging should be complemented by other approaches. Using simulated EHT data from a black hole emission model we consider an approach to Sgr A* image reconstruction based on a simple and computationally efficient analytical model that produces images similar to the synthetic ones. The model consists of an eccentric ring with a brightnes...