Positron Processes in the Sun

Gopalswamy, N.

doi:10.3390/atoms8020014

Cited by 5 publications

(3 citation statements)

References 43 publications

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“…For a long time, it was thought that only processes involving electrons contribute to the opacity of the Sun and the interstellar medium. However, positrons do exist in many regions of the Sun and the interstellar medium [51]. Therefore, it is necessary to consider positrons in calculations of opacity.…”

Section: Discussionmentioning

confidence: 99%

Photoejection from Various Systems and Radiative-Rate Coefficients

Bhatia

2022

Atoms

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Photoionization or photodetachment is an important process. It has applications in solar- and astrophysics. In addition to accurate wave function of the target, accurate continuum functions are required. There are various approaches, like exchange approximation, method of polarized orbitals, close-coupling approximation, R-matrix formulation, exterior complex scaling, the recent hybrid theory, etc., to calculate scattering functions. We describe some of them used in calculations of photodetachment or photoabsorption cross sections of ions and atoms. Comparisons of cross sections obtained using different approaches for the ejected electron are given. Furthermore, recombination rate coefficients also are also important in solar- and astrophysics and they have been calculated at various electron temperatures using the Maxwell velocity distribution function. Approaches based on the method of polarized orbitals do not provide any resonance structure of photoabsorption cross sections, in spite of the fact that accurate results have been obtained away from the resonance region and in the resonance region by calculating continuum functions to calculate resonance widths using phase shifts in the Breit–Wigner formula for calculating resonance parameters. Accurate resonance parameters in the elastic cross sections have been obtained using the hybrid theory and they compare well with those obtained using the Feshbach formulation. We conclude that accurate results for photoabsorption cross sections can be obtained using the hybrid theory.

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Section: Discussionmentioning

confidence: 99%

Photoejection from Various Systems and Radiative-Rate Coefficients

Bhatia

2022

Atoms

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“…SGREs >100 MeV are produced by >300 MeV protons precipitating from the solar corona into the solar chromosphere, where their interactions with the dense plasma layers create pions, which then decay into the observed >100 MeV gamma rays (e.g., Murphy et al 1987). The dominant source of >100 MeV gamma rays is neutral pion decay (e.g., Kafexhiu et al 2018;Gopalswamy 2020). Forrest et al (1985) first reported a clear detection of >40 MeV gamma rays that require pion production during the extended phase of the 1982 June 3 gamma-ray flare.…”

Section: Introductionmentioning

confidence: 99%

Speed and Acceleration of Coronal Mass Ejections Associated with Sustained Gamma-Ray Emission Events Observed by Fermi/LAT

Mäkelä,

Gopalswamy,

Akiyama

et al. 2023

ApJ

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The sustained gamma-ray emission (SGRE) from the Sun is a prolonged enhancement of >100 MeV gamma-ray emission that extends beyond the flare impulsive phase. The origin of the >300 MeV protons resulting in SGRE is debated, with both flares and shocks driven by coronal mass ejections (CMEs) being the suggested sites of proton acceleration. We compared the near-Sun acceleration and space speed of CMEs with “Prompt” and “Delayed” (SGRE) gamma-ray components. We found that “Delayed”-component-associated CMEs have higher initial accelerations and space speeds than “Prompt Only”-component-associated CMEs. We selected halo CMEs (HCMEs) associated with type II radio bursts (shock-driving HCMEs) and compared the average acceleration and space speed between HCME populations with or without SGRE events, major solar energetic particle (SEP) events, metric, or decameter-hectometric (DH) type II radio bursts. We found that the SGRE-producing HCMEs associated with a DH type II radio burst and/or a major SEP event have higher space speeds and especially initial accelerations than those without an SGRE event. We estimated the radial distances and speeds of the CME-driven shocks at the end time of the 2012 January 23 and March 7 SGRE events using white-light images of STEREO Heliospheric Imagers and radio dynamic spectra of Wind WAVES. The shocks were at the radial distances of 0.6–0.8 au and their speeds were high enough (≈975 km s−1 and ≈750 km s−1, respectively) for high-energy particle acceleration. Therefore, we conclude that our findings support the CME-driven shock as the source of >300 MeV protons.

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“…It has been known that there are positrons present in the Sun [8] and in interstellar space, as indicated by the detection of the 0.511 MeV line from the center of the galaxy due to the annihilation of the positron and electron pairs [9,10]. Positrons are produced due to various processes: when two protons collide, during the formation of 3 He nuclei, the decay of radioactive nuclei, and the decay of positive pions to muons, which further decay into positrons [11].…”

Section: Introductionmentioning

confidence: 99%

A Note on the Opacity of the Sun’s Atmosphere

Bhatia

Pesnell

2020

Atoms

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The opacity of the atmosphere of the Sun is due to processes such as Thomson scattering, bound–bound transitions and photodetachment (bound–free) of hydrogen and positronium ions. The well-studied free–free transitions involving photons, electrons, and hydrogen atoms are re-examined, while free–free transitions involving positrons are considered for the first time. Cross sections, averaged over a Maxwellian velocity distribution, involving positrons are comparable to those involving electrons. This indicates that positrons do contribute to the opacity of the atmosphere of the Sun. Accurate results are obtained because definitive phase shifts are known for electron–hydrogen and positron–hydrogen scattering.

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Positron Processes in the Sun

Cited by 5 publications

References 43 publications

Photoejection from Various Systems and Radiative-Rate Coefficients

Photoejection from Various Systems and Radiative-Rate Coefficients

Speed and Acceleration of Coronal Mass Ejections Associated with Sustained Gamma-Ray Emission Events Observed by Fermi/LAT

A Note on the Opacity of the Sun’s Atmosphere

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