Positron Annihilation Radiation from the Inner Galaxy

Kinzer, R. L.; Milne, Peter; Kurfess, J. D.; Strickman, M. S.; Johnson, W. N.; Purcell, W. R.

doi:10.1086/322371

Cited by 70 publications

(136 citation statements)

References 56 publications

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“…This gives a positronium fraction 5 f of 0.97-1.08, consistent with other determinations (Kinzer et al 2001;Jean et al 2004;Churazov et al 2005); although this is not the main goal of this analysis, it provides a consistency check on the analysis methods. While the positronium flux decreases by a factor at least ∼7 from |l| < 10…”

Section: Spectrasupporting

confidence: 87%

“…The inner Galactic ridge is known to be an intense source of continuum hard X-and soft γ-ray emission: hard X-ray emission was discovered in 1972 (Bleach et al 1972), and interstellar emission has subsequently been observed from keV to MeV energies by ASCA, Ginga, RXTE, OSSE, COMPTEL and most recently by Chandra and XMM-Newton. Most directly comparable to our INTEGRAL analysis are results from OSSE on the Compton Gamma Ray Observatory (Purcell et al 1996;Kinzer et al 1999Kinzer et al , 2001.…”

Section: Introductionsupporting

confidence: 81%

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Gamma-ray continuum emission from the inner Galactic region as observed with INTEGRAL/SPI

Strong¹,

Diehl²,

Halloin³

et al. 2005

A&A

117

100

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The diffuse continuum emission from the Galactic plane in the energy range 18-1000 keV has been studied using 16 Ms of data from the SPI instrument on INTEGRAL. With such an exposure we can exploit the imaging properties of SPI to achieve a good separation of point sources from the various diffuse components. Using a candidate-source catalogue derived with IBIS on INTEGRAL and a number of sky distribution models we obtained spectra resolved in Galactic longitude. We can identify spectral components of a diffuse continuum of power law shape with index about 1.7, a positron annihilation component with a continuum from positronium and the line at 511 keV, and a second, roughly power-law component from detected point sources. Our analysis confirms the concentration of positron annihilation emission in the inner region (|l| < 10• ), the disk (10 • < |l| < 30• ) being at least a factor 7 weaker in this emission. The power-law component in contrast drops by only a factor 2, showing a quite different longitude distribution and spatial origin. Detectable sources constitute about 90% of the total Galactic emission between 20 and 60 keV, but have a steeper spectrum than the diffuse emission, their contribution to the total emission dropping rapidly to a small fraction at higher energies. The spectrum of diffuse emission is compatible with RXTE and COMPTEL at lower and higher energies respectively. In the SPI energy range the flux is lower than found by OSSE, probably due to the more complete accounting for sources by SPI. The power-law emission is difficult to explain as of interstellar origin, inverse Compton giving at most 10%, and instead a population of unresolved point sources is proposed as a possible origin, AXPs with their spectral hardening above 100 keV being plausible candidates. We present a broadband spectrum of the Galactic emission from 10 keV to 100 GeV.

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Section: Spectrasupporting

confidence: 87%

Section: Introductionsupporting

confidence: 81%

Gamma-ray continuum emission from the inner Galactic region as observed with INTEGRAL/SPI

Strong¹,

Diehl²,

Halloin³

et al. 2005

A&A

117

100

View full text Add to dashboard Cite

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“…For the purposes of this illustrative exercise, we extend this bound up to 10 GeV (roughly consistent with the line limit we have derived). Each annihilation to an electron-positron pair produces two 511-keV photons either directly (7% of all annihilations) or by producing positronium and decaying (23.3% of all annihilations); the rest produce noncontributing continuum photons [24,26]. The resulting flux of 511-keV photons is (for Majorana particles) …”

Section: Discussionmentioning

confidence: 99%

Search with EGRET for a gamma ray line from the Galactic center

2007

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We search data from the Energetic Gamma Ray Experiment Telescope (EGRET) for a gamma-ray line in the energy range 0.1-10 GeV from the 10 10 region around the Galactic center. Our null results lead to upper limits to the line flux from the Galactic center. Such lines may have appeared if the dark matter in the Galactic halo is composed of weakly interacting massive particles (WIMPs) in the mass range 0.1-10 GeV. For a given dark-matter-halo model, our null search translates to upper limits to the WIMP two-photon annihilation cross section as a function of WIMP mass. We show that, for a toy model in which Majorana WIMPs in this mass range annihilate only to electron-positron pairs, these upper limits supersede those derived from measurements of the 511-keV line and continuum photons from internal bremsstrahlung at the Galactic center.

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“…Observations made by the NASA CGRO/OSSE and ESA INTEGRAL/SPI (Figs. E12, E13) instruments suggest a time-invariant emission that features an anomalously large contribution from the galactic bulge/halo, relative to emission at other wavelengths [90,49,51]. As it becomes increasingly clear that the emission is brightest in the direction of the galactic center, but that the emission appears truly diffuse (rather than from a point source near the galactic center), new theories are being explored to explain the bulge/halo positrons.…”

Section: Positron Astrophysicsmentioning

confidence: 99%

“…The 511 keV line-to-positronium continuum ratio suggests that upwards of 93% of positronelectron annihilations occur after first forming positronium [49]. A positronium fraction that high ________________________________________________________________________________________________ 17 …Witness to the Fires of Creation helps to exclude some media as the annihilation site for the bulk of the positron-electron annihilations.…”

Section: Positron Astrophysicsmentioning

confidence: 99%