Kavli Affiliate: Robert Goeke
| First 5 Authors: Akshay Suresh, Rohit Sharma, Divya Oberoi, Srijan B. Das, Victor Pankratius
| Summary:
Low radio frequency solar observations using the Murchison Widefield Array
have recently revealed the presence of numerous weak, short-lived and
narrow-band emission features, even during moderately quiet solar conditions.
These non-thermal features occur at rates of many thousands per hour in the
30.72 MHz observing bandwidth, and hence, necessarily require an automated
approach for their detection and characterization. Here, we employ continuous
wavelet transform using a mother Ricker wavelet for feature detection from the
dynamic spectrum. We establish the efficacy of this approach and present the
first statistically robust characterization of the properties of these
features. In particular, we examine distributions of their peak flux densities,
spectral spans, temporal spans and peak frequencies. We can reliably detect
features weaker than 1 SFU, making them, to the best of our knowledge, the
weakest bursts reported in literature. The distribution of their peak flux
densities follows a power law with an index of -2.23 in the 12-155 SFU range,
implying that they can provide an energetically significant contribution to
coronal and chromospheric heating. These features typically last for 1-2
seconds and possess bandwidths of about 4-5 MHz. Their occurrence rate remains
fairly flat in the 140-210 MHz frequency range. At the time resolution of the
data, they appear as stationary bursts, exhibiting no perceptible frequency
drift. These features also appear to ride on a broadband background continuum,
hinting at the likelihood of them being weak type-I bursts.
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