Ion acceleration and positron production and annihilation in solar flares (original) (raw)
Related papers
Particle Acceleration in Solar Flares and Enrichment of 3He and Heavy Ions
2008
We discuss possible mechanisms of acceleration of particles in solar flares and show that turbulence plays an important role in all the mechanism. It is also argued that stochastic particle acceleration by turbulent plasma waves is the most likely mechanism for production of the high energy electrons and ions responsible for observed radiative signatures of solar flares and for solar energetic particle or SEPs, and that the predictions of this model agrees well with many past and recent high spectral and temporal observations of solar flares. It is shown that, in addition, the model explains many features of SEPs that accompany flares. In particular we show that it can successfully explain the observed extreme enhancement, relative to photospheric values, of 3 He ions and the relative spectra of 3 He and 4 He. It has also the potential of explaining the relative abundances of most ions including the increasing enhancements of heavy ions with ion mass or mass-to-charge ratio.
On the Positronium Continuum and 0.511 MeV Line in Solar Flares
Chinese Journal of Astronomy and Astrophysics, 2004
We have studied the influence of the density of the annihilation region on the positronium continuum. A relation between the ratio 3γ/2γ and the density is explicitly given, with which one can derive directly from the observed 3γ/2γ the density where the annihilation occurs. A unique solution may be found from the observed width of the 0.511 MeV line. We applied the method to three flares observed by GRS/SMM. It is shown that due to the measuring uncertainties in the 0.511 MeV line width, we cannot distinguish a chromospheric source from a coronal source, though both accurately localized. To improve the measuring accuracy of the 0.511 MeV line and the ratio 3γ/2γ will be an important step for a better understanding of the annihilation process in solar flares.
Solar flare electron acceleration: Comparing theories and observations
Advances in Space Research, 2003
A popular scenario for electron acceleration in solar flares is transit-time damping of low-frequency MHD waves excited by reconnection and its outflows. The scenario requires several processes in sequence to yield energetic electrons of the observed large number. Until now there was very little evidence for this scenario, as it is even not clear where the flare energy is released. RHESSI measurements of bremsstrahlung by non-thermal flare electrons yield energy estimates as well as the position where the energy is deposited. Thus quantitative measurements can be put into the frame of the global magnetic field configuration as seen in coronal EUV line observations. We present RHESSI observations combined with TRACE data that suggest primary energy inputs mostly into electron acceleration and to a minor fraction into coronal heating and primary motion. The more sensitive and lower energy X-ray observations by RHESSI have found also small events (C class) at the time of the acceleration of electron beams exciting meter wave Type III bursts. However, not all RHESSI flares involve Type III radio emissions. The association of other decimeter radio emissions, such as narrowband spikes and pulsations, with X-rays is summarized in view of electron acceleration.
Enhancement of ionizing radiation during a solar flare from ionospheric data
1973
A theoretical approach is adopted to find out the energy increase in ; ionizing radiation during a flare from the available ionospheric data. The total ; ion production rate is equated with individual ion production rates due to four ; prominent spectral bands in the extreme ultraviolet and x-ray regions. Such ; equations, containing four unknowns corresponding to the photon fluxes, are ; formed for 17 heights in the range 150 to 230 km. The equations are solved for ; photon flux value for normal days and at the time of flare. (auth);
Rhessi observations of particle acceleration in solar flares
Advances in Space Research, 2003
... RHESSI has obtained the first high-resolution measurement of the positron annihilation line (Share et al. 2003b). ... Although there is a coronal source present at this time, perhaps above the loop top, it is a superhot thermal source, unlike the nonthermal source of Masuda et al. ...
The Astrophysical Journal, 2000
Observations of polarization of chromospheric lines in solar Ñares can constrain the energy Ñux in accelerated protons. In this paper we analyze recently reported observations of Ha linear polarization obtained during a rather well observed Ñare on 1989 June 20. Modeling of the magnitude and orientation of the Ha polarization provides a constraint on the Ñux of low energy keV) protons, while (Z200 simultaneous gamma-ray and hard X-ray observations provide constraints on the Ñuxes of MeV Z10 protons and keV electrons, respectively. These, plus information on the energetics of the low-Z50 temperature and high-temperature thermal emissions, permit evaluation of both the absolute and relative roles of electrons and protons in the Ñare energy budget. We Ðnd that accelerated protons with energies keV can contain a signiÐcant portion of the total energy released during the Ñare, consistent with Z200 a steep extrapolation of the proton spectrum to such relatively low energies. We discuss these results in light of a uniÐed electron/proton stochastic particle acceleration model and show that the energetics are indeed consistent with this large proton energy content.
Particle acceleration in solar flares: observations versus numerical simulations
Plasma Physics and Controlled Fusion, 2006
Solar flares are generally agreed to be impulsive releases of magnetic energy. Reconnection in dilute plasma is the suggested trigger for the coronal phenomenon. It releases up to 10 26 J, accelerates up to 10 38 electrons and ions and must involve a volume that greatly exceeds the current sheet dimension. The Ramaty High-Energy Solar Spectroscopic Imager satellite can image a source in the corona that appears to contain the acceleration region and can separate it from other x-ray emissions. The new observations constrain the acceleration process by a quantitative relation between spectral index and flux. We present recent observational results and compare them with theoretical modelling by a stochastic process assuming transit-time damping of fast-mode waves, escape and replenishment. The observations can only be fitted if additional assumptions on trapping by an electric potential and possibly other processes such as isotropization and magnetic trapping are made.
Electrons re-acceleration at the footpoints of Solar Flares
Hinode-3: The 3rd Hinode Science Meeting, 2010
Hinode's observations revealed a very dynamic and complex chromosphere. This require revisiting the assumption that the chromospheric footpoints of solar flares are areas where accelerated particles only lose energy due to collisions. Traditionally electrons are thought to be accelerated in the coronal part of the loop, then travel to the footpoints where they lose their energy and radiate the observed Hard X-ray. Increasing observational evidence challenges this assumption. We review the evidence against this assumption and present the new Local Re-acceleration Thick Target Model (LRTTM) where at the footpoints electrons receive a boost of re-acceleration in addition to the usual collisional loses. Such model may offer an alternative to the standard collisional thick target injection model (TTM) (Brown 1971) of solar HXR burst sources, requiring far fewer electrons and solving some recent problems with the TTM interpretation. We look at the different scenarios which could lead to such re-acceleration and present numerical results from one of them.
Proton acceleration in flares and magnetohydrodynamic solar activity
Solar Physics, 1993
The possibility of accelerated protons in solar flares having a sharp change in their spectral index is discussed. The analysis is based on the Tsytovich (1982, 1984, 1987a, b, c) acceleration model by MHD turbulence, which is shown to have different resonant conditions for non-relativistic and relativistic particles. The different resonant condition is shown to result in a sharp change in the accelerated proton spectral index, even in the absence of any peculiarity in the spectra of the MHD turbulence. Time scales for accelerated protons to relativistic energies are also derived, and shown to be consistent with observations. We also show that the threshold energy for electron acceleration by low frequency MHD turbulence is much greater than for proton acceleration. The turbulence therefore preferentially accelerates protons.
Advances in Space Research, 2005
Observations of hard X-ray (HXR)/c-ray continuum and c-ray lines produced by energetic electrons and ions, respectively, colliding with the solar atmosphere, have shown that large solar flares can accelerate ions up to many GeV and electrons up to hundreds of MeV. Solar energetic particles (SEPs) are observed by spacecraft near 1 AU and by ground-based instrumentation to extend up to similar energies as in large SEP events, but it appears that a different acceleration process, one associated with fast coronal mass ejections is responsible. Much weaker SEP events are observed that are generally rich in electrons, 3 He, and heavy elements. The energetic particles in these events appear to be similar to those accelerated in flares. The Ramaty high energy solar spectroscopic imager (RHESSI) mission provides high-resolution spectroscopy and imaging of flare HXRs and c-rays. Such observations can provide information on the location, energy spectra, and composition of the flare accelerated energetic particles at the Sun. Here, preliminary comparisons of the RHESSI observations with observations of both energetic electron and ion near 1 AU are reviewed, and the implications for the particle acceleration and escape processes are discussed.