A Technique for Detecting Propagating Coronal Waves with the VLA

Details A Technique for Detecting Propagating Coronal Waves with the VLA A Technique for Detecting Propagating Coronal Waves with the VLA

Jan 2012

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2012aas...21914401s&link_type=abstract

American Astronomical Society, AAS Meeting #219, #144.01

Astronomy and Astrophysics

Astronomy

Scientific paper

There is currently great interest in measuring outward-propagating waves and disturbances in the solar corona. These waves and disturbances are naturally interpreted as the Alfvén waves which heat the corona and drive the solar wind. An ideal way of measuring these waves is via Faraday rotation measurements with the Very Large Array (VLA) of an extended radio source viewed through the corona. In principle, the same rotation measure time series should be observed for each polarized component in the source, but lagged by the propagation time across the source. The difficulty with this type of measurement is that VLA maps must be made with a fast cadence, i.e. 10 - 30 seconds, to resolve the expected propagation time across a typical source with an angular extent of 40 - 60 arcseconds. Such a short integration time results in noisy maps and nearly precludes measurements of the polarization position angle χ. In this paper, I discuss an alternative technique for measuring coronal rotation measure time series for two or more components of an extended radio source, using the directly measured intensities of the Stokes parameters Q and U. The technique was applied to VLA observations of the radio galaxy 3C228 during the coronal occultation of August 2003. Although the signal-to-noise environment in this case was not sufficient to measure propagating disturbances, the exercise does show that the algorithm and data processing method work. The data also show weak evidence for rotation measure fluctuations on time scales of a few minutes. Observations with the Expanded Very Large Array (EVLA) should permit a successful application of the technique. This research was supported at the University of Iowa by grant ATM-0956901 from the National Science Foundation.

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