High-Resolution Observation of the Solar Positron-Electron Annihilation Line

Abstract

The Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) has observed the positron-electron annihilation line at 511 keV produced during the 2002 July 23 solar flare. The shape of the line is consistent with annihilation in two vastly different solar environments. It can be produced by formation of positronium by charge exchange in flight with hydrogen in a quiet solar atmosphere at a temperature of ∼6000 K. However, the measured upper limit to the ratio (ratio of annihilation photons in the positronium continuum to the number 3g/2g in the line) is only marginally consistent with what is calculated for this environment. The annihilation line can also be fitted by a thermal Gaussian having a width of keV (FWHM), indicating temperatures of 8.1 ‫ע‬ 1.1 ∼ K. The measured ratio does not constrain the density when the annihilation takes place in 5 (4-7) # 10 3g/2g such an ionized medium, although the density must be high enough to slow down the positrons. This would require the formation of a substantial mass of atmosphere at transition-region temperatures during the flare. Subject headings: Sun: flares -Sun: particle emission -Sun: X-rays, gamma rays L86 SHARE ET AL.Vol. 595

Time delay between γ-ray lines and hard X-ray emissions during the 23 July 2002 solar flare interpreted by a trap plus precipitation model

“…Temporal evolution of X-ray and γ-ray line emissions Figure 1 shows the temporal evolution of the hard X-ray emissions at 150 keV and 1 MeV and of the gamma-ray line time profile. These time profiles are obtained from the spectroscopic analysis presented in Share et al (2003). The spectral analysis is performed for successive time intervals of 20 s and results from the fitting to observed count spectra of a model photon spectrum including a double power law for the bremsstrahlung continuum, a nuclear de-excitation line function made of 15 narrow and broad Gaussians (Smith et al 2003), a neutron-capture line , a α− 4 He fusion line complex between ∼400 and 500 keV , and the solar annihilation line at 511 keV and its positronium continuum.…”

INTEGRAL/SPI and Fermi/GBM Observation of the 2012 March 7th Solar Flares

“…2 ) 0.132 ± 0.005 GBM fluence (ph/cm 2 ) 67 ± 3 SPI flux (ph/s/cm 2 ) 0.115 ± 0.008 0.094 ± 0.009 SPI fluence (ph/cm 2 ) 80 ± 6 47 ± 5 SPI fluence total** (ph/cm 2 ) 85 ± 8 65 ± 7 * As marked by the greem bars in Figure 1 ** Total fluence of the line in the respective flares…”

“…Line intensities and their temporal evolution and line shape studies give information on properties of the solar atmosphere and the accelerated particle composition and their momenta and angular distributions [1]. Line shape studies which require high energy resolution spectroscopy, have been applied to several solar flares since the launch of the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) and INTEGRAL in 2002 [2][3][4] [5]. INTEGRAL is not designed for studying solar physics, but with its Germanium camera's high energy resolution and the 3 days uninterrupted observation, it makes a unique instrument to study gamma-ray lines in strong solar flares.…”

Solar Gamma-Ray Line Spectroscopy – Physics of a Flaring Star

“…It has been fit by folding an incident photon spectrum containing electron bremsstrahlung and nuclear lines through the instrument response function. The overall fit to the data is good and the individual components of the fit are shown separately in the figure; Share et al (2003a) list the best fitting parameters. The curves show the full instrumental response to the incident radiation, including both events in which the full energy has been absorbed and those in which only part of the energy has been absorbed (as reflected in the lower energy Compton continuum).…”

“…RHESSI made the first high-resolution observation of the solar positron-electron annihilation line during the July 23 flare (Share et al 2003a). We plot the measured line in the left panel of Figure 10, after removing contributions from the instrument and atmosphere.…”