Coronal γ-Ray Bremsstrahlung from Solar Flare-accelerated Electrons

Krucker, S.; Hurford, G. J.; MacKinnon, A. L.; Shih, Albert Y.; Lin, R. P.

doi:10.1086/588381

Cited by 71 publications

(72 citation statements)

References 28 publications

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“…According to the CGRO/BATSE light curve, the flux decreased almost twice during this time interval, hence in the maximum the photons more energetic than 600 keV were emitted. Krucker et al (2008b) interpret the coronal γ-ray emission as relativistic electron-electron bremsstrahlung at energies perhaps of a few MeV. Therefore, these observations directly imply that flare-accelerated MeV electrons reside stably in the corona, losing their energy collisionally and producing γ-ray continuum.…”

Section: Coronal γ-Ray Sourcesmentioning

confidence: 90%

The YOHKOH survey of partially occulted flares in hard X-rays

Tomczak

2009

A&A

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Context. Modern solar X-ray imagers did not breakthrough the problem of detailed diagnostics of faint hard X-ray sources in the presence of stronger ones. This is the case of the impulsive phase of solar flares in which footpoint sources are usually stronger than loop-top ones. Aims. For this aim, flares being partially occulted by the solar limb, are the best reservoir of our knowledge about hard X-ray loop-top sources. Recently, the survey of partially occulted flares observed by the RHESSI has been published . The extensive Yohkoh database still awaits such activities. This work is an attempt to fill this gap. Methods. Among from 1286 flares in the Yohkoh Hard X-ray Telescope Flare Catalogue (Sato et al. 2006), for which the hard X-ray images had been enclosed, we identified 98 events that occurred behind the solar limb. We investigated their hard X-ray spectra and spatial structure. Results. We found that in most cases the hard X-ray spectrum of partially occulted flares consists of two components, non-thermal and thermal, which are co-spatial. The photon energy spectra of the partially occulted flares are systematically steeper than spectra of the non-occulted flares. Such a difference we explain as a consequence of intrinsically dissimilar conditions ruling in coronal parts of flares, in comparison with the footpoints which usually dominate the hard X-ray emission of disk flares. At least two reasons of the difference should be taken into consideration: (1) stronger contamination of hard X-rays with emission of thermal plasma, (2) different mechanism in which non-thermal electrons radiate their energy. For events unbiased with the thermal component the difference, ∆γ =γ LT −γ FP , is equal to 1.5. Conclusions. A schematic picture, in which thin-target mechanism is responsible for hard X-ray emission of loop-top sources and thick-target mechanism -for emission of footpoint sources, is modified by the presence of some coronal thick-target sources. At least a part of them suggests a magnetic trapping. Investigated flares do not respond the overall (global) magnetic configuration of the solar corona. For their characteristics conclusive is rather the local magnetic configuration in which they were developed.

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Section: Coronal γ-Ray Sourcesmentioning

confidence: 90%

The YOHKOH survey of partially occulted flares in hard X-rays

Tomczak

2009

A&A

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“…RHESSI hard X-ray imaging observations in the 250Y450 keV range show two hard X-ray footpoints and a fainter third source in between the footpoints ( Hurford et al 2006). This third source is unlikely a footpoint source but is rather emission from the corona (Krucker et al 2008), although projection effects do not allow us to unambiguously identify the origin of this source.…”

Section: Imagingmentioning

confidence: 91%

Radio Submillimeter and γ‐Ray Observations of the 2003 October 28 Solar Flare

Trottet

Krucker

Lüthi

et al. 2008

ApJ

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Radio observations at 210 GHz taken by the Bernese Multibeam Radiometer for KOSMA ( BEMRAK ) are combined with hard X-ray and -ray observations from the SONG instrument on board CORONA-F and the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI ) to investigate high-energy particle acceleration during the energetic solar flare of 2003 October 28. Two distinct components at submillimeter wavelengths are found. The first is a gradual, long-lasting (>30 minutes) component with large apparent source sizes ($60 00 ). Its spectrum below $200 GHz is consistent with synchrotron emission from flare-accelerated electrons producing hard X-ray and -ray bremsstrahlung assuming a magnetic field strength of !200 G in the radio source and a confinement time of the radioemitting electrons in the source of less than 30 s. The other component is impulsive and starts simultaneously with high-energy (>200 MeV nucleon À1 ) proton acceleration and the production of pions. The derived radio source size is compact ( 10 00 ), and the emission is cospatial with the location of precipitating flare-accelerated >30 MeV protons as seen in -ray imaging. The close correlation in time and space of radio emission with the production of pions suggests that synchrotron emission of positrons produced in charged-pion decay might be responsible for the observed compact radio source. However, order-of-magnitude approximations rather suggest that the derived numbers of positrons from charged-pion decay are probably too small to account for the observed radio emission. Synchrotron emission from energetic electrons therefore appears as the most likely emission mechanism for the compact radio source seen in the impulsive phase, although it does not account for its close correlation, in time and space, with pion production.

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“…In the reconnection model, one also expects the particles to be accelerated along the open field lines reaching into the upper corona. Hard X-ray observations have been made at the loop top of flares (Masuda et al 1994), but it is not until recently that RHESSI has been able to detect a signature of independent particle distributions on either side of an assumed current sheet (Krucker et al 2008). This investigation strongly supports the picture where the acceleration region is located in the corona, and that particles are accelerated in both directions away from the local reconnection region.…”

Section: Introductionmentioning

confidence: 99%

Test particle acceleration in a numerical MHD experiment of an anemone jet

Rosdahl

Galsgaard²

2010

A&A

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Aims. To use a 3D numerical MHD experiment representing magnetic flux emerging into an open field region as a background field for tracing charged particles. The interaction between the two flux systems generates a localised current sheet where MHD reconnection takes place. We investigate how efficiently the reconnection region accelerates charged particles and what kind of energy distribution they acquire. Methods. The particle tracing is done numerically using the Guiding Center Approximation on individual data sets from the numerical MHD experiment. Results. We derive particle and implied photon distribution functions having power law forms, and look at the impact patterns of particles hitting the photosphere. We find that particles reach energies far in excess of those seen in observations of solar flares. However the structure of the impact region in the photosphere gives a good representation of the topological structure of the magnetic field.

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Coronal γ-Ray Bremsstrahlung from Solar Flare-accelerated Electrons

Cited by 71 publications

References 28 publications

The YOHKOH survey of partially occulted flares in hard X-rays

The YOHKOH survey of partially occulted flares in hard X-rays

Radio Submillimeter and γ‐Ray Observations of the 2003 October 28 Solar Flare

Test particle acceleration in a numerical MHD experiment of an anemone jet

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