<i>RHESSI</i>Observations of the Solar Flare Iron‐Line Feature at 6.7 keV

Phillips, K. J. H.; Chifor, C.; Dennis, B. R.

doi:10.1086/505518

Cited by 41 publications

(53 citation statements)

References 22 publications

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“…We analysed the output from a single RHESSI detector 4F only because of its fine energy resolution of 0.98 keV (Smith et al 2002). Also, it produces a photon spectrum close to the mean spectrum of all front detectors usable for spectroscopy (Phillips et al 2006). Moreover, the drm_mod function can only be used to fit single-detector spectra.…”

Section: Rhessimentioning

confidence: 99%

Diagnostics of non-thermal distributions in solar flare spectra observed by RESIK and RHESSI

Kulinová

Kašparová

Dzifčáková

et al. 2011

A&A

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Context. During solar flares an enormous amount of energy is released, and the charged particles, like electrons, are accelerated. These non-thermal electrons interact with the plasma in various parts of solar flares, where the distribution function of electrons can therefore be non-Maxwellian. Aims. We focus on the non-thermal components of the electron distribution in the keV range and analyse high-energy resolution X-ray spectra detected by RESIK and RHESSI for three solar flares. Methods. In the 2-4 keV range we assume that the electron distribution can be modelled by an n-distribution. Using a method of line-intensity ratios, we analyse allowed and satellite lines of Si observed by RESIK and estimate the parameters of this n-distribution. At higher energies we explore RHESSI bremsstrahlung spectra. Adopting a forward-fitting approach and thick-target approximation, we determine the characteristics of injected electron beams. Results. RHESSI non-thermal component associated with the electron beam is correlated well with presence of the non-thermal n-distribution obtained from the RESIK spectra. In addition, such an n-distribution occurs during radio bursts observed in the 0.61-15.4 GHz range. Furthermore, we show that the n-distribution could also explain RHESSI emission below ∼5 keV. Therefore, two independent diagnostics methods indicate the flare plasma being affected by the electron beam can have a non-thermal component in the ∼2-5 keV range, which is described by the n-distribution well. Finally, spectral line analysis reveals that the n-distribution does not occupy the same location as the thermal component detected by RHESSI at ∼10 keV.

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Section: Rhessimentioning

confidence: 99%

Diagnostics of non-thermal distributions in solar flare spectra observed by RESIK and RHESSI

Kulinová

Kašparová

Dzifčáková

et al. 2011

A&A

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“…The thermal plasma emission was modeled with an isothermal component (describing the free-free and free-bound continuum) and one Gaussian function to fit the 6.7 keV Fe line feature (method described in detail by Phillips et al 2006). The observed high-energy emission ( > ∼ 10 keV) was modeled as a nonthermal component with a power-law distribution I(E) ∝ E −γ , where γ represents the power-law index of the photon flux spectrum.…”

Section: September 13 (Event 1: On-disk)mentioning

confidence: 99%

X-ray precursors to flares and filament eruptions

Chifor¹,

Tripathi²,

Mason³

et al. 2007

A&A

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Aims. To study preflare X-ray brightenings as diagnostics of the destabilisation of flare-associated erupting filaments/prominences. Methods. We combine new observations from the Transition Region and Coronal Explorer (TRACE) and the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI), as well as revisit events reported in the literature to date, in order to scrutinise the preflare activity during eight flare-associated filament eruptions. Results. The preflare activity occurs in the form of discrete, localised X-ray brightenings observed between 2 and 50 min before the impulsive phase of the flare and filament acceleration. These transient preflare brightenings are situated on or near (within 10 of) the polarity inversion line (PIL), coincident with emerging and/or canceling magnetic flux. The filaments begin to rise from the location of the preflare brightenings. In five out of eight events, the preflare brightenings were observed beneath the filament channel, close to the filament footpoint first observed to rise. Both thermal and nonthermal hard X-ray emissions during the preflare enhancement were detected with RHESSI, suggesting that both plasma heating and electron acceleration occurred at this time. The main energy release during the impulsive phase of the flare is observed close to (within 50 of) the preflare brightenings. The fast-rise phase of the filament eruption starts at the same time as the onset of the main flare or up to 5 min later. Conclusions. The preflare brightenings are precursors to the flare and filament eruption. These precursors represent distinct, localised instances of energy release, rather than a gradual energy release prior to the main flare. The X-ray precursors represent clearly observable signatures in the early stages of the eruption. Together with the timing of the filament fast-rise at or after the main flare onset, the X-ray precursors provide evidence for a tether-cutting mechanism initially manifested as localised magnetic reconnection being a common trigger for both flare emission and filament eruption.

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“…Also, analysis of broad-band data from the RHESSI instrument in its A0 attenuator state (Phillips et al 2006) similarly indicates that there is a non-flaring component of emission, with temperature corresponding to the active region, as well as a hotter flare component.…”

Section: Observationsmentioning

confidence: 94%

“…It is assumed, as was found from the RESIK flare observations of Ar xvii line ratios (Sylwester et al 2008) and analysis of broad-band spectra from RHESSI in its A0 attenuator state (Phillips et al 2006), that a two-component emission measure distribution describes the observed spectra, a low-temperature component (1-4 MK) appropriate for the Na x and Ne ix emission from the non-flaring active region and The Na x lines were included in the synthesis program from the Aggarwal et al (2009) atomic data (Sect. 3.3) and the Na ix satellites, both those excited by dielectronic recombination and those formed by inner-shell excitation, from the data discussed in Sect.…”

Section: Synthetic Spectramentioning

confidence: 99%

Highly Ionized sodium X-ray line emission from the solar corona and the abundance of sodium

Phillips¹,

Aggarwal

Landi³

et al. 2010

A&A

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Context. The Na x X-ray lines between 10.9 and 11.2 Å have attracted little attention but are of interest since they enable an estimate of the coronal abundance of Na to be made. This is of great interest in the continuing debate on the nature of the FIP (first ionization potential) effect.Aims. Observations of the Na x lines with the Solar Maximum Mission Flat Crystal Spectrometer and a rocket-borne X-ray spectrometer are used to measure the Na/Ne abundance ratio, i.e. the ratio of an element with very low FIP to one with high FIP. Methods. New atomic data are used to generate synthetic spectra which are compared with the observations, with temperature and the Na/Ne abundance ratio as free parameters. Results. Temperature estimates from the observations indicate that the line emission is principally from non-flaring active regions, and that the Na/Ne abundance ratio is 0.07 ± 50%. Conclusions. The Na/Ne abundance ratio is close to a coronal value for which the abundances of low-FIP elements (FIP < 10 eV) are enhanced by a factor of 3 to 4 over those found in the photosphere. For low-temperature (T e 1.5 MK) spectra, the presence of Fe xvii lines requires that either a higher-temperature component is present or a revision of ionization or recombination rates is needed.

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RHESSIObservations of the Solar Flare Iron‐Line Feature at 6.7 keV

Cited by 41 publications

References 22 publications

Diagnostics of non-thermal distributions in solar flare spectra observed by RESIK and RHESSI

Diagnostics of non-thermal distributions in solar flare spectra observed by RESIK and RHESSI

X-ray precursors to flares and filament eruptions

Highly Ionized sodium X-ray line emission from the solar corona and the abundance of sodium

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