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Abstract: A promising source of the positrons that contribute through annihilation tothe diffuse Galactic 511keV emission is the beta-decay of unstable nuclei like56Ni and 44Ti synthesised by massive stars and supernovae. Although a largefraction of these positrons annihilate in the ejecta of SNe-SNRs, nopoint-source of annihilation radiation appears in the INTEGRAL-SPI map of the511keV emission. We exploit the absence of detectable annihilation emissionfrom young local SNe-SNRs to derive constraints on the transport of MeVpositrons inside SN-SNR ejecta and their escape into the CSM-ISM, both aspectsbeing crucial to the understanding of the observed Galactic 511keV emission. Wesimulated 511keV lightcurves resulting from the annihilation of the decaypositrons of 56Ni and 44Ti in SNe-SNRs and their surroundings using a simplemodel. We computed specific 511keV lightcurves for Cas A, Tycho, Kepler,SN1006, G1.9+0.3 and SN1987A, and compared these to the upper-limits derivedfrom INTEGRAL-SPI observations. The predicted 511keV signals from positronsannihilating in the ejecta are below the sensitivity of the SPI instrument byseveral orders of magnitude, but the predicted 511keV signals for positronsescaping the ejecta and annihilating in the surrounding medium allowed toderive upper-limits on the positron escape fraction of ~13% for Cas A, ~12% forTycho, ~30% for Kepler and ~33% for SN1006. The transport of ~MeV positronsinside SNe-SNRs cannot be constrained from current observations of the 511keVemission from these objects, but the limits obtained on their escape fractionare consistent with a nucleosynthesis origin of the positrons that give rise tothe diffuse Galactic 511keV emission.



Autor: Pierrick Martin, Jacco Vink, Sarka Jiraskova, Pierre Jean, Roland Diehl

Fuente: https://arxiv.org/







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