Wavelet-based Characterization of Small-scale Solar Emission Features at Low Radio Frequencies

Journal Article · Sat Jul 01 00:00:00 EDT 2017 · Astrophysical Journal

DOI:https://doi.org/10.3847/1538-4357/AA774A· OSTI ID:22663459

Suresh, A. ^[1]; Sharma, R.; Oberoi, D. ^[2]; Das, S. B. ^[3]; Pankratius, V.; Lonsdale, C. J.; Cappallo, R. J.; Corey, B. E.; Kratzenberg, E. ^[4]; Timar, B. ^[5]; Bowman, J. D. ^[6]; Briggs, F. ^[7]; Deshpande, A. A. ^[8]; Emrich, D. ^[9]; Goeke, R. ^[10]; Greenhill, L. J. ^[11]; Hazelton, B. J. ^[12]; Johnston-Hollitt, M. ^[13]; Kaplan, D. L. ^[14]; others, and

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1. Indian Institute of Science Education and Research, Pune-411008 (India)
2. National Centre for Radio Astrophysics, Tata Institute for Fundamental Research, Pune 411007 (India)
3. Indian Institute of Science Education and Research, Kolkata-741249 (India)
4. MIT Haystack Observatory, Westford, MA 01886 (United States)
5. California Institute of Technology, Pasadena, CA 91125 (United States)
6. School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287 (United States)
7. Research School of Astronomy and Astrophysics, Australian National University, Canberra, ACT 2611 (Australia)
8. Raman Research Institute, Bangalore 560080 (India)
9. International Centre for Radio Astronomy Research, Curtin University, Bentley, WA 6102 (Australia)
10. Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139 (United States)
11. Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138 (United States)
12. Department of Physics, University of Washington, Seattle, WA 98195 (United States)
13. School of Chemical and Physical Sciences, Victoria University of Wellington, P.O. Box 600, Wellington 6140 (New Zealand)
14. Department of Physics, University of Wisconsin–Milwaukee, Milwaukee, WI 53201 (United States)

Low radio frequency solar observations using the Murchison Widefield Array have recently revealed the presence of numerous weak short-lived narrowband emission features, even during moderately quiet solar conditions. These nonthermal 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 s 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.

• OSTI ID: 22663459
• Journal Information: Astrophysical Journal, Vol. 843, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
COSMIC RADIO SOURCES
DETECTION
DISTRIBUTION
EMISSION
FLUX DENSITY
MHZ RANGE
RADIOWAVE RADIATION
SOLAR RADIATION
SPECTRA
SPECTRAL DENSITY
SUN
TIME RESOLUTION