High-resolution observation of the solar positron-electron annihilation line

Gerald H. Share; Ronald J. Murphy; Jeffrey G. Skibo; David M. Smith; Hugh S. Hudson; Robert P. Lin; Albert Y. Shih; Brian R. Dennis; Richard A. Schwartz; Benzion Kozlovsky

doi:10.1086/378174

High-resolution observation of the solar positron-electron annihilation line

Gerald H. Share^*, Ronald J. Murphy, Jeffrey G. Skibo, David M. Smith, Hugh S. Hudson, Robert P. Lin, Albert Y. Shih, Brian R. Dennis, Richard A. Schwartz, Benzion Kozlovsky

^*Corresponding author for this work

School of Physics and Astronomy

Research output: Contribution to journal › Article › peer-review

46 Scopus citations

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 3γ/2γ ratio (ratio of annihilation photons in the positronium continuum to the number 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 8.1 ± 1.1 keV (FWHM), indicating temperatures of ∼(4-7) × 10⁵ K. The measured 3γ/2γ ratio does not constrain the density when the annihilation takes place in 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.

Original language	English
Pages (from-to)	L85-L88
Journal	Astrophysical Journal
Volume	595
Issue number	2 II
DOIs	https://doi.org/10.1086/378174
State	Published - 1 Oct 2003

Funding

Funders	Funder number
National Aeronautics and Space Administration	DPR W10049, DPR W19746
U.S. Naval Research Laboratory
School of Public Health, University of California Berkeley	NAS 5-98033
Israel Science Foundation

Keywords

Sun: X-rays, gamma rays
Sun: flares
Sun: particle emission

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10.1086/378174

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@article{202e3dafef8248f39ff718419ccd6241,

title = "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 3γ/2γ ratio (ratio of annihilation photons in the positronium continuum to the number 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 8.1 ± 1.1 keV (FWHM), indicating temperatures of ∼(4-7) × 105 K. The measured 3γ/2γ ratio does not constrain the density when the annihilation takes place in 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.",

keywords = "Sun: X-rays, gamma rays, Sun: flares, Sun: particle emission",

author = "Share, {Gerald H.} and Murphy, {Ronald J.} and Skibo, {Jeffrey G.} and Smith, {David M.} and Hudson, {Hugh S.} and Lin, {Robert P.} and Shih, {Albert Y.} and Dennis, {Brian R.} and Schwartz, {Richard A.} and Benzion Kozlovsky",

note = "Funding Information: This work was supported NASA DPR W19746 and DPR W10049 at the NRL. The work at the UCB and NASA Goddard was supported by NASA contract NAS 5-98033. B. Kozlovsky acknowledges the Israeli Science Foundation for support. The positronium calculations used here were derived from a computer code written by Jeffrey Skibo while he was at NRL; a paper that he was preparing with coauthors Nidhal Guessoum and Reuven Ramaty has not yet been submitted for publication. We thank John Mariska for discussing evidence of high densities at transition-region temperatures during flares.",

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doi = "10.1086/378174",

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journal = "Astrophysical Journal",

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AU - Share, Gerald H.

AU - Murphy, Ronald J.

AU - Skibo, Jeffrey G.

AU - Smith, David M.

AU - Hudson, Hugh S.

AU - Lin, Robert P.

AU - Shih, Albert Y.

AU - Dennis, Brian R.

AU - Schwartz, Richard A.

AU - Kozlovsky, Benzion

N1 - Funding Information: This work was supported NASA DPR W19746 and DPR W10049 at the NRL. The work at the UCB and NASA Goddard was supported by NASA contract NAS 5-98033. B. Kozlovsky acknowledges the Israeli Science Foundation for support. The positronium calculations used here were derived from a computer code written by Jeffrey Skibo while he was at NRL; a paper that he was preparing with coauthors Nidhal Guessoum and Reuven Ramaty has not yet been submitted for publication. We thank John Mariska for discussing evidence of high densities at transition-region temperatures during flares.

PY - 2003/10/1

Y1 - 2003/10/1

N2 - 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 3γ/2γ ratio (ratio of annihilation photons in the positronium continuum to the number 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 8.1 ± 1.1 keV (FWHM), indicating temperatures of ∼(4-7) × 105 K. The measured 3γ/2γ ratio does not constrain the density when the annihilation takes place in 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.

AB - 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 3γ/2γ ratio (ratio of annihilation photons in the positronium continuum to the number 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 8.1 ± 1.1 keV (FWHM), indicating temperatures of ∼(4-7) × 105 K. The measured 3γ/2γ ratio does not constrain the density when the annihilation takes place in 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.

KW - Sun: X-rays, gamma rays

KW - Sun: flares

KW - Sun: particle emission

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SN - 0004-637X

VL - 595

SP - L85-L88

JO - Astrophysical Journal

JF - Astrophysical Journal

IS - 2 II

ER -

High-resolution observation of the solar positron-electron annihilation line

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