Annihilation emission from young supernova remnants

Abstract

A promising source of the positrons that contribute through annihilation to the diffuse Galactic 511keV emission is the beta-decay of unstable nuclei like 56Ni and 44Ti synthesised by massive stars and supernovae. Although a large fraction of these positrons annihilate in the ejecta of SNe/SNRs, no point-source of annihilation radiation appears in the INTEGRAL/SPI map of the 511keV emission. We exploit the absence of detectable annihilation emission from young local SNe/SNRs to derive constraints on the transport of MeV positrons inside SN/SNR ejecta and their escape into the CSM/ISM, both aspects being crucial to the understanding of the observed Galactic 511keV emission. We simulated 511keV lightcurves resulting from the annihilation of the decay positrons of 56Ni and 44Ti in SNe/SNRs and their surroundings using a simple model. We computed specific 511keV lightcurves for Cas A, Tycho, Kepler, SN1006, G1.9+0.3 and SN1987A, and compared these to the upper-limits derived from INTEGRAL/SPI observations. The predicted 511keV signals from positrons annihilating in the ejecta are below the sensitivity of the SPI instrument by several orders of magnitude, but the predicted 511keV signals for positrons escaping the ejecta and annihilating in the surrounding medium allowed to derive upper-limits on the positron escape fraction of ~13% for Cas A, ~12% for Tycho, ~30% for Kepler and ~33% for SN1006. The transport of ~MeV positrons inside SNe/SNRs cannot be constrained from current observations of the 511keV emission from these objects, but the limits obtained on their escape fraction are consistent with a nucleosynthesis origin of the positrons that give rise to the diffuse Galactic 511keV emission.

15 pages, 11 figures, accepted for publication in A&A

References in corpus (11)

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• Continuum gamma-ray emission from light dark matter positrons and electrons
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• Microquasars as sources of positron annihilation radiation
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Cited by in corpus (10)

• Supernova remnants: the X-ray perspective
• Supernova Ejecta in the Youngest Galactic Supernova Remnant G1.9+0.3
• Interacting dark matter contribution to the Galactic 511 keV gamma ray emission: constraining the morphology with INTEGRAL/SPI observations
• Monte Carlo modelling of the propagation and annihilation of nucleosynthesis positrons in the Galaxy
• Supernova bounds on axion-like particles coupled with nucleons and electrons
• Galactic annihilation emission from nucleosynthesis positrons
• Radioactivity and Electron Acceleration in Supernova Remnants
• Searching for the 511 keV annihilation line from galactic compact objects with the IBIS gamma ray telescope
• On the quadruple Beltrami fields in thermally relativistic electron-positron-ion plasma
• Radioactive Decay