Time Profiles and Photon Spectra of Solar Hard X-Rays

Beek, H. F. van; Feiter, L. D. De; Jager, C. de

doi:10.1007/978-94-010-2172-2_34

Cited by 17 publications

(6 citation statements)

References 3 publications

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“…Under these conditions, the rapid changes of the radio emission pattern are more in favor of rapid changes of the magnetic structure involved in the acceleration rather than to electron diffusion from a single acceleration site. This study performed on one flare is consistent with previous results (Machado et al 1988;Willson et al 1990) and is in agreement with the earlier idea that a hard X-ray flare is made of several elementary bursts (van Beek, de Feiter, & de Jager 1974). It shows, however, that each elementary burst involves a slightly different site of the acceleration volume.…”

Section: Coronal Signatures Of the Accelerated Electrons: Evolution Osupporting

confidence: 93%

Solar Hard X-Ray and Gamma-Ray Observations from GRANAT

Vilmer

1994

International Astronomical Union Colloquium

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Hard X-rays and gamma-rays are the most direct signature of the energetic electrons and ions which are accelerated during solar flares. Since the beginning of 1990 the PHEBUS instrument and the SIGMA anticoincidence shield aboard GRANAT have provided hard X-ray and gamma-ray observations of solar bursts in the energy range 0.075-124 and 0.200-15 MeV, respectively. After a brief description of the experiments, we present some results obtained on solar bursts recorded in 1990 and 1991 June. Special emphasis is given to the results related with particle acceleration during solar flares.The first part of the review is devoted to the constraints obtained on the electron acceleration timescale through the analysis of the temporal characteristics of the bursts. Combined studies of hard X-ray and gamma-ray emissions from PHEBUS and radio emissions from the Nançay Multifrequency Radioheliograph are used to infer constraints on the coronal magnetic topology involved in flares. The characteristics (location, spectrum) of the radio-emitting sources are found to vary within a flare from one hard X-ray peak to the other. Hard X-ray and gamma-ray burst onsets and rapid increases of the > 10 MeV emission are coincident with changes in the associated radio emission pattern. These results will be discussed in the context of the flare energy release.The second part of the paper concerns the heliocentric angle distribution of > 10 MeV events and presents more detailed observations of some of the largest flares in the gamma-ray line and the high-energy domains produced by ultrarelativistic electrons and > 100 MeV nucleon−1 ions. The PHEBUS observations of the gamma-ray line flare of 11 June 1991 have been used to deduce the hardness of the accelerated ion spectrum. The link between the main part of the flare and the late long-lasting >50 MeV emission detected by EGRET/COMPTON is discussed. Finally some observations of the large 1990 May 24 flare which produced a large neutron event at ground level are presented.Subject headings: acceleration of particles — Sun: flares — Sun: radio radiation — Sun: X-rays, gamma rays

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Section: Coronal Signatures Of the Accelerated Electrons: Evolution Osupporting

confidence: 93%

Solar Hard X-Ray and Gamma-Ray Observations from GRANAT

Vilmer

1994

International Astronomical Union Colloquium

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“…ejection of energetic electrons. The authors (Van Beek et al, 1974) consider these short bursts to be the essential physical phenomena which when clustered together in large numbers, as may be the case in the August 4 flare, constitute the conventional high energy flare. Figure 2 shows the time-integrated solar and background gamma ray pulse height spectra accumulated between 0624-0633 UT.…”

Section: Channel Numbermentioning

confidence: 99%

Observations of solar gamma ray continuum between 360 keV and 7 MeV on August 4, 1972

et al. 1975

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Measurements were made of the time-averaged gamma ray energy loss spectrum in the energy range 360 keV to 7 MeV by the gamma ray detector on the OSO-7 satellite during the 3B flare on August 4, 1972. The differential photon spectrum unfolded from this spectrum after subtracting the background spectrum and contributions from gamma ray lines is best described by a power law with spectral index of 3.4d_0.3 between 360-700 keV and by an exponential law of the form exp (--E/Eo) with E0=l.0• MeV above 700 keV. It is suggested that this spectrum is due to nonthermal electron bremsstrahlung from a population of electrons, with a strong break in the spectrum at 2 MeV. Since the observational data indicates that the matter number density must be n~ ~> 5 • 101~ cm -a in the production region, the number of electrons above 100 keV required to explain the results is ~< 2 x 10 a4.

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“…Since the pioneering works of Frost (1969) and van Beek et al (1974), it was proposed that bursts are built up with what were originally called, in X-rays, the Elementary Flare Bursts (EFB) by de Jager & de Jonge (1978). Similarly at microwaves, Kaufmann et al (1980) later extended this concept to smaller time scales, adding a quasi-quantization hypothesis.…”

Section: Introductionmentioning

confidence: 99%

Multi-resolution wavelet analysis of high time resolution millimeter wavelength observations of solar bursts

Castro

Raulin

Mandrini

et al. 2001

A&A

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Abstract. By means of the wavelet representation of multi-resolution analysis, we study millimeter wavelength (mm-w) radio solar bursts obtained at 48 GHz with high time resolution (≤8 ms); observed at Itapetinga (Brazil). The multi-resolution analysis decomposes the signal locally both in time and in frequency, allowing us to identify the different temporal structures which underlie the flux density time series and the transient phenomena characteristic of solar bursts. The analysis was applied to the flux time profile of four solar bursts observed at a mm-w, studying separately the pre-flare, impulsive and post-flare phases when possible. We find that a wide range of time scales contributes to the radio flux. The minimum time scale found for the impulsive phase is 32 ms, after which the noise dominates the emission; the maximum is 8 s. Pre-and post-flare phases have a minimum time scale of 256 ms and a maximum between 1 to 8 s. Multi-resolution "spectral indexes", which are a measure of the self-similar behavior of the signal, are in some cases bigger for the impulsive phase than for the pre-and post-flare phases. We find that as the flux becomes higher the contribution from shorter time scales is enhanced.

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Time Profiles and Photon Spectra of Solar Hard X-Rays

Cited by 17 publications

References 3 publications

Solar Hard X-Ray and Gamma-Ray Observations from GRANAT

Solar Hard X-Ray and Gamma-Ray Observations from GRANAT

Observations of solar gamma ray continuum between 360 keV and 7 MeV on August 4, 1972

Multi-resolution wavelet analysis of high time resolution millimeter wavelength observations of solar bursts

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