Impulsive phase of flares in soft X-ray emission

Antonucci, E.; Gabriel, A. H.; Acton, L. W.; Culhane, J. L.; Doyle, J. G.; Leibacher, J. W.; Machado, M. E.; Orwig, L. E.; Rapley, C. G.

doi:10.1007/bf00151147

Cited by 293 publications

(125 citation statements)

References 14 publications

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“…First, the expected outflow of hot gas into the corona during the hard phase was detected with SMM (Antonucci et al 1982). Second, the properties of the H a emission in bright points in the impulsive phase agree well with those calculated in models (Bruevich 1995).…”

Section: Accelerated Particles In Impulsive Solar Flaressupporting

confidence: 78%

Physical Processes During Impulsive Solar and Stellar Flares

Katsova

Livshits

1995

International Astronomical Union Colloquium

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Investigations of impulsive flares on both the Sun and red dwarf stais during more than 30 years allow us to arrive at quite definite conclusions. Here we will consider impulsive events; on the Sun the impulsive phase of a flare is observed as a hard X-ray burst with the emission of photons with energies E > 30 keV up to the γ-ray range. At the same time microwave radio bursts, and sometimes UV and optical continuum bursts are registered. Typical durations of these processes are ∼l-3 min. In this time interval other kinds of flare emission like soft X-ray (2-10 keV) emission, meter radio bursts and Balmer line emission begin to rise, but their maxima occur later on, in the gradual (thermal) phase of the flare.Impulsive stellar flares are often observed as a significant increase in optical continuum, especially in the U-band, of similar duration (1-3 min), and this time interval is, like in the solar case, the rise phase of the soft X-ray emission.Modern observations demonstrate that both the impulsive phase of a flare or an impulsive flare develops in low-lying loops. Earlier only indirect evidence existed in optical and radio data. Recently, however, the heights of the hard X-ray sources in impulsive solar events were determined directly from YOHKOH’s HXT (Kosugi 1994, Masuda 1994) (Fig. 1a). Statistically, the height of the hard X-ray source in the 14-23 keV range is 9700 ± 2000 km above the photosphere, and this height reduces to 6500 km in the 53-93 keV range. Besides two hard X-ray sources in the loop footpoints, a third hard X-ray source exists at the top of the loop at least in some cases. The authors of this experiment suppose that the appearance of this loop-top source is due to reconnection in the impulsive phase. Note that the reconnection begins close to the apex of the loop, when this loop is filled by hot plasma that evaporated from both footpoints.

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Section: Accelerated Particles In Impulsive Solar Flaressupporting

confidence: 78%

Physical Processes During Impulsive Solar and Stellar Flares

Katsova

Livshits

1995

International Astronomical Union Colloquium

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“…At the onset, blue shifts of the order of 150 km s −1 to 300 km s −1 were also observed, occasionally even 500 km s −1 . Antonucci et al (1982) studied soft X-ray emission observed with SMM, and also found turbulent velocities of more than 100 km s −1 and upflows with speeds up to 400 km s −1 . Similar results were obtained from the Bragg Crystal Spectrometer (BCS) on Yohkoh (Mariska 1994).…”

Section: Flaresmentioning

confidence: 97%

Observations of the Sun at Vacuum-Ultraviolet Wavelengths from Space. Part II: Results and Interpretations

et al. 2007

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In Part I of this review, the concepts of solar vacuum-ultraviolet (VUV) observations were outlined together with a discussion of the space instrumentation used for the investigations. A section on spectroradiometry provided some quantitative results on the solar VUV radiation without considering any details of the solar phenomena leading to the radiation. Here, in Part II, we present solar VUV observations over the last decades and their interpretations in terms of the plasma processes and the parameters of the solar atmosphere, with emphasis on the spatial and thermal structures of the chromosphere, transition region and corona of the quiet Sun. In addition, observations of active regions, solar flares and prominences are included as well as of small-scale events. Special sections are devoted to the elemental composition of the solar atmosphere and theoretical considerations on the heating of the corona and the generation of the solar wind.

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“…Doschek et al 1979), the Solar Maximum Mission (SMM) X-ray polychromator (XRP) Bent Crystal Spectrometer (BCS) (cf. Antonucci et al 1982), and from the Bragg Crystal Spectrometer (BCS) on YOHKOH (see, e.g., Bentley et al 1994). The observations were mainly of Hand He-like lines (in particular Ca xix), which are formed over a very broad range of temperatures, 8-25 MK (1 MK = 1 × 10 6 K).…”

Section: Introductionmentioning

confidence: 99%

The 22 May 2007 B-class flare: new insights fromHinodeobservations

Zanna¹,

Mitra-Kraev²,

Bradshaw

et al. 2010

A&A

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We present multi-wavelength observations of a small B-class flare which occurred on the Sun on 2007 May 22. The observations include data from Hinode, GOES, TRACE and the Nobeyama Radioheliograph. We obtained spatially and spectrally-resolved information from the Hinode EUV Imaging Spectrometer (EIS) during this event. The temporal and temperature coverage of the EIS observations provides new insights into our understanding of chromospheric evaporation and cooling. The flare showed many "typical" features, such as brightenings in the ribbons, hot (10 MK) loop emission and subsequent cooling. We also observed a new feature, strong (up to 170 km s −1 ) blue-shifted emission in lines formed around 2-3 MK, located at the footpoints of the 10 MK coronal emission and within the ribbons. Electron densities at 2 MK in the kernels are high, of the order of 10 11 cm −3 , suggesting a very narrow layer where the chromospheric evaporation occurs. We have run a non-equilibrium hydrodynamic numerical simulation using the HYDRAD code to study the cooling of the 10 MK plasma, finding good agreement between the predicted and observed temperatures, densities and ion populations. Line blending for some potentially useful diagnostic lines for flares, which are observed with Hinode/EIS, is also discussed.

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Impulsive phase of flares in soft X-ray emission

Cited by 293 publications

References 14 publications

Physical Processes During Impulsive Solar and Stellar Flares

Physical Processes During Impulsive Solar and Stellar Flares

Observations of the Sun at Vacuum-Ultraviolet Wavelengths from Space. Part II: Results and Interpretations

The 22 May 2007 B-class flare: new insights fromHinodeobservations

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