Daily Image
08-08-2018
Twinkle, Twinkle, little Quasar - Observing the Solar Wind with LOFAR
| Submitter: | David McKenna |
| Description: | Interplanetary scintillation is a phenomenon seen when a compact radio source is observed close to the Sun and manifests itself as variations of intensity on short time scales caused by density variations in the solar wind. The outflow of different solar wind streams with different densities and powerful events such as Coronal Mass Ejections (CMEs) cause variation in the strength of the scintillation, thus leading to measurements of this parameter being a valuable tool to probe the solar wind and observe CMEs in the interplanetary medium. However, extraction of a "scintillation index" as a measure of the strength of the scintillation with a phased array system such as LOFAR is not as straightforward as from using a traditional dish system. In this project we took observations of 3C48 and 3C147 with simultaneous interferometric imaging using the Dutch array (at sub 10th of a second, a first for LOFAR), tied-array beams using the full core, with a ring of off-source reference beams, and "fly's eye" observations using the international stations on various dates during the spring. The imaging data were initially processed using the method outlined by Morgan et al. (2017) for extracting scintillation indices with the MWA wide-field images, and used as a reference baseline to compare approaches for implementing similar methodologies to extract scintillation indices from the beam-formed data sets. Both data sets were then used to implement a power spectrum method introduced by Manoharan (1993), where the area under the spectrum is used to assess the amount of scintillation, a method typically applied to single station time series data but now also applicable to the fast imaging we undertook with LOFAR. We obtained consistent results between the imaging and beam-formed data, demonstrating both that reliable scintillation indices can be calculated from LOFAR data, and that the faster processing and less data-intensive beam-formed data are sufficient for this. The technique was applied also to 3C147 LOFAR data from September 2017 to identify and observe the passage of the fastest CME of the current solar cycle! The video is a WSClean image cube from an observation of 3C48 on the 18th of April, at a sampling rate of 12.04Hz and an excessively-detailed pixel resolution, showing the source scintillating due to the solar wind. |
| Copyright: | David McKenna |
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