Wavelet-based Characterization of Small-scale Solar Emission Features at Low Radio Frequencies
| Autor: | Rohit Sharma, Judd D. Bowman, Alan R. Whitney, Lincoln J. Greenhill, Victor Pankratius, Eric Kratzenberg, Bryna J. Hazelton, Thiagaraj Prabu, Colin J. Lonsdale, A. Roshi, Brian E. Corey, B. Timar, Divya Oberoi, David Emrich, Robert F. Goeke, Frank H. Briggs, N. Udaya Shankar, M. Waterson, Randall B. Wayth, Roger J. Cappallo, Daniel A. Mitchell, Steven Tingay, Alan E. E. Rogers, Ravi Subrahmanyan, Miguel F. Morales, Eric R. Morgan, Andrew Williams, K. S. Srivani, Stephen R. McWhirter, Melanie Johnston-Hollitt, Avinash A. Deshpande, Rachel L. Webster, Stephen M. Ord, M. J. Lynch, Akshay Suresh, Justin C. Kasper, Srijan Bharati Das, David L. Kaplan, Christopher L. Williams |
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| Jazyk: | angličtina |
| Rok vydání: | 2017 |
| Předmět: |
Physics
010504 meteorology & atmospheric sciences Frequency drift FOS: Physical sciences Astronomy and Astrophysics Murchison Widefield Array Astrophysics 01 natural sciences Corona Nanoflares Narrowband Wavelet Astrophysics - Solar and Stellar Astrophysics Space and Planetary Science 0103 physical sciences Radio frequency 010303 astronomy & astrophysics Continuous wavelet transform Solar and Stellar Astrophysics (astro-ph.SR) 0105 earth and related environmental sciences |
| Popis: | 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. 15 pages, 14 figures, Accepted for publication in ApJ |
| Databáze: | OpenAIRE |
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