Chen, X. , Kontar, E. P. , Clarkson, D. L. and Chrysaphi, N. (2023) The frequency ratio and time delay of solar radio emissions with fundamental and harmonic components. Monthly Notices of the Royal Astronomical Society, 520(2), pp. 3117-3126. (doi: 10.1093/mnras/stad325)
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Abstract
Solar radio bursts generated through the plasma emission mechanism produce radiation near the local plasma frequency (fundamental emission) and double the plasma frequency (harmonic). While the theoretical ratio of these two frequencies is close to 2, simultaneous observations give ratios ranging from 1.6 to 2, suggesting either a ratio different from 2, a delay of the fundamental emission, or both. To address this long-standing question, we conducted high frequency, high time resolution imaging spectroscopy of type III and type J bursts with fine structures for both the fundamental and harmonic components with LOFAR between 30 and 80 MHz. The short-lived and narrow frequency-band fine structures observed simultaneously at fundamental and harmonic frequencies give a frequency ratio of 1.66 and 1.73, similar to previous observations. However, frequency-time cross-correlations suggest a frequency ratio of 1.99 and 1.95 with a time delay between the F and H emissions of 1.00 and 1.67 s, respectively for each event. Hence, simultaneous frequency ratio measurements different from 2 are caused by the delay of the fundamental emission. Among the processes causing fundamental emission delays, anisotropic radio-wave scattering is dominant. Moreover, the levels of anisotropy and density fluctuations reproducing the delay of fundamental emissions are consistent with those required to simulate the source size and duration of fundamental emissions. Using these simulations we are able to, for the first time, provide quantitative estimates of the delay time of the fundamental emissions caused by radio-wave propagation effects at multiple frequencies, which can be used in future studies.
| Item Type: | Articles |
|---|---|
| Status: | Published |
| Refereed: | Yes |
| Glasgow Author(s) Enlighten ID: | Kontar, Professor Eduard and Clarkson, Dr Daniel and Chrysaphi, Dr Nicolina and Chen, Dr Xingyao |
| Authors: | Chen, X., Kontar, E. P., Clarkson, D. L., and Chrysaphi, N. |
| College/School: | College of Science and Engineering > School of Physics and Astronomy |
| Journal Name: | Monthly Notices of the Royal Astronomical Society |
| Publisher: | Oxford University Press |
| ISSN: | 0035-8711 |
| ISSN (Online): | 1365-2966 |
| Published Online: | 31 January 2023 |
| Copyright Holders: | Copyright © 2023 The Authors |
| First Published: | First published in Monthly Notices of the Royal Astronomical Society 520(2): 3117-3126 |
| Publisher Policy: | Reproduced under a Creative Commons License |
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