Multifrequency observations of a remarkable solar radio burst

S. M. White, M. R. Kundu, T. S. Bastian, D. E. Gray, G. J. Hurford, T. Kucera, John H Bieging

Research output: Contribution to journalArticle

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Abstract

Observations of an impulsive solar radio burst from three observatories are presented. The striking observational aspects of this flare are that the time profile was identical throughout at 8.6, 15, and 86 GHz, that the spectrum was apparently flat from 15 to 86 GHz, and that there was a sharp cutoff in the spectrum between 5.0 and 8.6 GHz. The simplest interpretation of the cutoff, namely as a plasma frequency effect, leads to the conclusion that there was exceptionally high-density material in the solar corona (∼ 5 × 1011 cm-3). Very Large Array images at 15 GHz show a single loop structure which brightened uniformly and showed little change in size during the whole impulsive phase. The flat spectrum is consistent with optically thin thermal bremsstrahlung emission, but the lack of observed soft X-ray emission and other properties of the flare cannot easily be accommodated by this mechanism. We also explore the possibility that the emission is optically thick due to thermal absorption of nonthermal gyrosynchrotron emission, or optically thin gyrosynchrotron emission absorbed by high-density material intervening along the line of sight. Both of these explanations also face difficulties.

Original languageEnglish (US)
Pages (from-to)656-664
Number of pages9
JournalAstrophysical Journal
Volume384
Issue number2
StatePublished - 1992

Fingerprint

solar radio bursts
radio
flares
cut-off
thermal absorption
nonthermal radiation
Very Large Array (VLA)
solar corona
plasma frequencies
bremsstrahlung
line of sight
observatories
corona
observatory
plasma
profiles
x rays

Keywords

  • Radiation mechanisms: cyclotron and synchrotron
  • Sun: flares
  • Sun: radio radiation

ASJC Scopus subject areas

  • Space and Planetary Science

Cite this

White, S. M., Kundu, M. R., Bastian, T. S., Gray, D. E., Hurford, G. J., Kucera, T., & Bieging, J. H. (1992). Multifrequency observations of a remarkable solar radio burst. Astrophysical Journal, 384(2), 656-664.

Multifrequency observations of a remarkable solar radio burst. / White, S. M.; Kundu, M. R.; Bastian, T. S.; Gray, D. E.; Hurford, G. J.; Kucera, T.; Bieging, John H.

In: Astrophysical Journal, Vol. 384, No. 2, 1992, p. 656-664.

Research output: Contribution to journalArticle

White, SM, Kundu, MR, Bastian, TS, Gray, DE, Hurford, GJ, Kucera, T & Bieging, JH 1992, 'Multifrequency observations of a remarkable solar radio burst', Astrophysical Journal, vol. 384, no. 2, pp. 656-664.
White SM, Kundu MR, Bastian TS, Gray DE, Hurford GJ, Kucera T et al. Multifrequency observations of a remarkable solar radio burst. Astrophysical Journal. 1992;384(2):656-664.
White, S. M. ; Kundu, M. R. ; Bastian, T. S. ; Gray, D. E. ; Hurford, G. J. ; Kucera, T. ; Bieging, John H. / Multifrequency observations of a remarkable solar radio burst. In: Astrophysical Journal. 1992 ; Vol. 384, No. 2. pp. 656-664.
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AU - Kundu, M. R.

AU - Bastian, T. S.

AU - Gray, D. E.

AU - Hurford, G. J.

AU - Kucera, T.

AU - Bieging, John H

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N2 - Observations of an impulsive solar radio burst from three observatories are presented. The striking observational aspects of this flare are that the time profile was identical throughout at 8.6, 15, and 86 GHz, that the spectrum was apparently flat from 15 to 86 GHz, and that there was a sharp cutoff in the spectrum between 5.0 and 8.6 GHz. The simplest interpretation of the cutoff, namely as a plasma frequency effect, leads to the conclusion that there was exceptionally high-density material in the solar corona (∼ 5 × 1011 cm-3). Very Large Array images at 15 GHz show a single loop structure which brightened uniformly and showed little change in size during the whole impulsive phase. The flat spectrum is consistent with optically thin thermal bremsstrahlung emission, but the lack of observed soft X-ray emission and other properties of the flare cannot easily be accommodated by this mechanism. We also explore the possibility that the emission is optically thick due to thermal absorption of nonthermal gyrosynchrotron emission, or optically thin gyrosynchrotron emission absorbed by high-density material intervening along the line of sight. Both of these explanations also face difficulties.

AB - Observations of an impulsive solar radio burst from three observatories are presented. The striking observational aspects of this flare are that the time profile was identical throughout at 8.6, 15, and 86 GHz, that the spectrum was apparently flat from 15 to 86 GHz, and that there was a sharp cutoff in the spectrum between 5.0 and 8.6 GHz. The simplest interpretation of the cutoff, namely as a plasma frequency effect, leads to the conclusion that there was exceptionally high-density material in the solar corona (∼ 5 × 1011 cm-3). Very Large Array images at 15 GHz show a single loop structure which brightened uniformly and showed little change in size during the whole impulsive phase. The flat spectrum is consistent with optically thin thermal bremsstrahlung emission, but the lack of observed soft X-ray emission and other properties of the flare cannot easily be accommodated by this mechanism. We also explore the possibility that the emission is optically thick due to thermal absorption of nonthermal gyrosynchrotron emission, or optically thin gyrosynchrotron emission absorbed by high-density material intervening along the line of sight. Both of these explanations also face difficulties.

KW - Radiation mechanisms: cyclotron and synchrotron

KW - Sun: flares

KW - Sun: radio radiation

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