First Images of a Solar Flare at Millimeter Wavelengths

Silva, Adriana V. R.; White, S. M.; Lin, R. P.; Pater, Imke de; Shibasaki, Κ.; Hudson, H. S.; Kundu, M. R.

doi:10.1086/309918

Cited by 17 publications

(11 citation statements)

References 12 publications

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“…Thus the centimeter radio emission confirms the differences between loop-top and footpoints found in X-ray sources. In addition to gyrosynchrotron emission, Wang et al (1994) and Silva et al (1996) report thermal loop-top radio emission at a temperature of about 30 MK, in rough agreement with the hot thermal component of the coronal soft X-ray source. These imaging results confirm previous interpretations of thermal flare radiation at centimeter wavelengths, known as "post-burst increase" and "gradual rise and fall" bursts with correlated soft X-ray emission (Kundu 1965).…”

Section: Particle Acceleration Sitementioning

confidence: 61%

Flare Observations

Benz

2016

Living Rev Sol Phys

511

317

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Solar flares are observed at all wavelengths from decameter radio waves to gamma-rays beyond 1 GeV. This review focuses on recent observations in EUV, soft and hard X-rays, white light, and radio waves. Space missions such as RHESSI, Yohkoh, TRACE, SOHO, and more recently Hinode and SDO have enlarged widely the observational base. They have revealed a number of surprises: Coronal sources appear before the hard X-ray emission in chromospheric footpoints, major flare acceleration sites appear to be independent of coronal mass ejections, electrons, and ions may be accelerated at different sites, there are at least 3 different magnetic topologies, and basic characteristics vary from small to large flares. Recent progress also includes improved insights into the flare energy partition, on the location(s) of energy release, tests of energy release scenarios and particle acceleration. The interplay of observations with theory is important to deduce the geometry and to disentangle the various processes involved. There is increasing evidence supporting magnetic reconThis article is a revised version of https://doi.org/10.12942/lrsp-2008-1. Change summary Major revision, updated and expanded. Change details Significant new results from RHESSI and SDO are included. In particular, Sect. 3.4 on "Emissions from above the coronal source" was added (including two new figures) and Sect. 3.2 on "Coronal hard X-ray sources" was expanded. New observations of flares in white light are reported (replaced Fig. 25 with a movie), as well as recent multi-wavelength observations in radio waves and gamma-rays combined with hard X-rays. Four references were removed and 49 new references added. Arnold O. Benz nection as the basic cause. While this process has become generally accepted as the trigger, it is still controversial how it converts a considerable fraction of the energy into non-thermal particles. Flare-like processes may be responsible for large-scale restructuring of the magnetic field in the corona as well as for its heating. Large flares influence interplanetary space and substantially affect the Earth's ionosphere. Flare scenarios have slowly converged over the past decades, but every new observation still reveals major unexpected results, demonstrating that solar flares, after 150 years since their discovery, remain a complex problem of astrophysics including major unsolved questions. Electronic supplementary material

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Section: Particle Acceleration Sitementioning

confidence: 61%

Flare Observations

Benz

2016

Living Rev Sol Phys

511

317

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“…Interferometric observations of flares have been made by the Berkeley, Illinois, Maryland Array (BIMA) at Hatcreek, California, at a wavelength of 3 mm since 1989 . With the recent upgrade of BIMA to a nine-element, 2D array, mm-λ imaging is now possible (Silva et al 1996, Raulin et al 1997. The construction of the Millimeter Array in the coming decade will provide vastly improved sensitivity and imaging at mm-λ and sub-mm-λ thereby supplying important new opportunities to study the most energetic electrons in flares with a resolution and image fidelity far in advance of any instrument now available.…”

Section: Instrumentationmentioning

confidence: 99%

Radio Emission From Solar Flares

Bastian

Benz²,

Gary

1998

Annu. Rev. Astron. Astrophys.

588

417

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Radio emission from solar flares offers a number of unique diagnostic tools to address long-standing questions about energy release, plasma heating, particle acceleration, and particle transport in magnetized plasmas. At millimeter and centimeter wavelengths, incoherent gyrosynchrotron emission from electrons with energies of tens of kilo electron volts to several mega electron volts plays a dominant role. These electrons carry a significant fraction of the energy released during the impulsive phase of flares. At decimeter and meter wavelengths, coherent plasma radiation can play a dominant role. Particularly important are type III and type III-like radio bursts, which are due to upward-and downwarddirected beams of nonthermal electrons, presumed to originate in the energy release site. With the launch of Yohkoh and the Compton Gamma-Ray Observatory, the relationship between radio emission and energetic photon emissions has been clarified. In this review, recent progress on our understanding of radio emission from impulsive flares and its relation to X-ray emission is discussed, as well as energy release in flare-like phenomena (microflares, nanoflares) and their bearing on coronal heating.

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“…When compared to hard X-ray observations, many of the flares observed with BIMA indicate a flattening of the electron energy spectrum towards higher energies (e.g. Lim et al 1992;Kundu et al 1994;Silva et al 1996;Raulin et al 1999). A similar change of the spectral slope has been reported for combined observations of hard X-rays and microwaves (Marsh et al 1981), whereas hard X-ray/γ-ray spectroscopy in the energy range of 30 keV-70 MeV allowed the direct observation of broken energy spectra (e.g.…”

Section: Introductionmentioning

confidence: 99%

First observation of a solar X-class flare in the submillimeter range with KOSMA

Lüthi¹,

Magun²,

Miller³

2004

A&A

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Abstract. We present the first solar flare observations with the KOSMA submillimeter telescope at 230 and 345 GHz. The GOES X2.0 flare on April 12, 2001 was also observed at millimeter and centimeter wavelengths, as well as in soft and hard X-rays. It exhibits both an impulsive phase of nonthermal gyrosynchrotron radiation and an extended phase of strong thermal free-free emission in the millimeter and submillimeter range. As in previous observations, a mismatch between the electron energy spectral indices, inferred from the millimeter and hard X-ray data, exists and is interpreted as a flattening of the energy spectrum above a break energy of several hundred keV. The observed thermal emission closely follows the shape of the mm/submm flux density time profile predicted from soft X-ray observations. As the observed absolute flux densities exceed the predicted ones by a factor of ∼1.5-3.4, both the mm/submm emission and the soft X-rays must be thermal bremsstrahlung with a common energy source, but from locations with different plasma parameters. KOSMA observations allowed an estimate of source locations and sizes for the nonthermal and thermal sources. All of them coincide within 0.2 arcmin and with those seen in soft and hard X-rays. Surprisingly, the thermal submillimeter source diameters at 230 and 345 GHz (42 and 70 arcsec respectively) increase with frequency.

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First Images of a Solar Flare at Millimeter Wavelengths

Cited by 17 publications

References 12 publications

Flare Observations

Flare Observations

Radio Emission From Solar Flares

First observation of a solar X-class flare in the submillimeter range with KOSMA

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