Solar observations with a millimeter-wavelength Array

White, S. M.; Kundu, M. R.

doi:10.1007/bf00155185

Cited by 62 publications

(30 citation statements)

References 60 publications

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“…By dividing different SXT filter images, the temperature and emission measure, EM, are determined for every pixel in the SXT images (Vaiana, Krieger, & Timothy 1973;McTiernan et al 1993). The optically thin ( Ͻ Ͻ 1) free-free flux density is given by (White & Kundu 1992) S free ϭ 1.577 ϫ 10 9 EM 55…”

Section: Discussionmentioning

confidence: 99%

“…The nonthermal millimeter emission is produced by electrons with energies of approximately 1 MeV (White & Kundu 1992), the same electrons that are responsible for the ␥-ray continuum (Kawabata et al 1982). Nonthermal emission is generally produced in the impulsive flash phase of flares.…”

Section: Introductionmentioning

confidence: 99%

“…Interferometers offer a powerful advantage for solar observations: by correlating the signal of two antennas, structures larger than the fringe spacing will be resolved out (White & Kundu 1992). Thus, the quiet-Sun background (scale size of the solar disk) measured by an interferometer will be much lower.…”

Section: Introductionmentioning

confidence: 99%

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First Images of a Solar Flare at Millimeter Wavelengths

Silva¹,

White²,

Lin³

et al. 1996

ApJ

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We present the first high spatial resolution images of a solar flare at millimeter wavelengths. On 1994 August 17, a GOES soft X-ray class M1 flare was observed by the Berkeley-Illinois-Maryland Array at 86 GHz by the Nobeyama 17 GHz array and by the Yohkoh spacecraft. The flare displayed both a prominent impulsive phase in microwaves and a gradual phase that lasted over 30 minutes. The millimeter data were taken only during the gradual phase. The millimeter images show a source with a size of 18Љ, a peak brightness temperature of 110 6 K, and maximum optical depth of 0.09. At both X-ray and radio wavelengths, the emitting region appeared to be compact (=20Љ). In soft X-ray, the images are resolved into two sources: one located at a footpoint and the other at the top of the flaring loop. The millimeter emission is consistent with the predicted free-free flux from an isothermal temperature (114 MK) loop-top source, a multitemperature footpoint source with a hot (122 MK), and a cold (112 MK) component. Most (80%) of the millimeter flux density originates from the top of the magnetic loop, and the footpoint contribution is only 20%.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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First Images of a Solar Flare at Millimeter Wavelengths

Silva¹,

White²,

Lin³

et al. 1996

ApJ

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“…However, higherfrequency nonthermal gyrosynchrotron emission requires emission at ever higher harmonics of the electron gyrofrequency, and this makes it sensitive to electrons with much higher energies than are required for microwave emission (MeV and higher energies rather than tens to hundreds of keV : Ramaty 1969;White & Kundu 1992;Ramaty et al 1994, and Figure 2.1). Bremsstrahlung is increasingly inefficient as electron energy increases because faster electrons suffer less deflection by a nucleus.…”

Section: Sol2002-04-21t01:51 (X15)mentioning

confidence: 99%

The Relationship Between Solar Radio and Hard X-ray Emission

White¹,

Benz²,

Christe³

et al. 2011

High-Energy Aspects of Solar Flares

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This review discusses the complementary relationship between radio and hard X-ray observations of the Sun using primarily results from the era of the Reuven Ramaty High Energy Solar Spectroscopic Imager satellite. A primary focus of joint radio and hard X-ray studies of solar flares uses observations of nonthermal gyrosynchrotron emission at radio wavelengths and bremsstrahlung hard X-rays to study the properties of electrons accelerated in the main flare site, since it is well established that these two emissions show very similar temporal behavior. A quantitative prescription is given for comparing the electron energy distributions derived separately from the two wavelength ranges: this is an important application with the potential for measuring the magnetic field strength in the flaring region, and reveals significant differences between the electrons in different energy ranges. Examples of the use of simultaneous data from the two wavelength ranges to derive physical conditions are then discussed, including the case of microflares, and the comparison of images at radio and hard X-ray wavelengths is presented. There have been puzzling results obtained from observations of solar flares at millimeter and submillimeter wavelengths, and the comparison of these results with corresponding hard X-ray data is presented. Finally, the review discusses the association of hard X-ray releases with radio emission at decimeter and meter wavelengths, which is dominated by plasma emission (at lower frequencies) and electron cyclotron maser emission (at higher frequencies), both coherent emission mechanisms that require small numbers of energetic electrons. These comparisons show broad general associations but detailed correspondence remains more elusive.

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“…Nevertheless, this emission is thought to be produced by > MeV electrons (White & Kundu 1992), the same ones that generate the 100-1000 keV hard X-rays. The results described here were obtained with the Solar Submillimeter Telescope (Figure 8), a 1.5 m dish installed at the CASLEO Observatory in the Argentinean Andes at an altitude of 2500 m (Kaufmann et al 2001).…”

Section: Flare At Submillimeter Wavelengthsmentioning

confidence: 99%

Variability of the solar spectral irradiance and energetic particles

Silva-Válio¹

2009

Proc. IAU

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Abstract. The total spectral irradiance of the Sun is seen to vary on many time scales. Three timescales are more prominent: (1) the longest one of about 11 years; (2) an intermediate timescale of the order of a few weeks; and (3) the shortest variation from hours to seconds. Every 11 years, the total solar irradiance periodically shows intervals of great activity and periods of almost no activity. The peak to peak variability, however, is less than 0.1%. This periodic variation of 11 years is called the solar cycle, which main tracer are sunspots. During times of maximum activity, there are many sunspots on the surface of the Sun, whereas during minimum there may be none. Sunspots are dark, and therefore cool, regions of enhanced magnetic fields of about a few hundred Gauss, that usually appear in groups on the solar photosphere. Basically, the solar cycle is regulated by the magnetic dynamo acting below the solar surface. Right now, the Sun is going through a time of minimum activity. The sunspot lifetime is of the order of one to two weeks, and are thus responsible for the intermediate variability timescale. The magnetic loops seen in ultraviolet and X-ray images have their footpoints anchored on sunspots. The most energetic phenomena of solar activity are flares and coronal mass ejections. Flares are large explosions that occur on the solar atmosphere and may last from a few seconds to hours. A solar flare is caused by a sudden, and yet unpredicted, energy release high above the magnetic loops. This magnetic energy is then used into particle acceleration and heating of the surrounding atmosphere. Both the energetic particles and the hot gas produce emission throughout the whole electromagnetic spectrum, from the very energetic gamma-rays all the way to long radio waves. From the observation of the emission produced during flares it is possible to infer the energetic particles spectra and thus have a clue on the acceleration mechanism that produced these particles. The recent findings of flare observations at gamma-rays by the RHESSI satellite and at high radio frequencies by the Solar Submillimeter Telescope are presented and discussed.

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Solar observations with a millimeter-wavelength Array

Cited by 62 publications

References 60 publications

First Images of a Solar Flare at Millimeter Wavelengths

First Images of a Solar Flare at Millimeter Wavelengths

The Relationship Between Solar Radio and Hard X-ray Emission

Variability of the solar spectral irradiance and energetic particles

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