Classical-Nova Contribution to the Milky Way's ${}^{26}$Al Abundance: Exit Channel of the Key ${}^{25}$Al($p,\gamma$)${}^{26}$Si Resonance

Abstract

Classical novae are expected to contribute to the 1809-keV Galactic $\gamma$-ray emission by producing its precursor ${}^{26}$Al, but the yield depends on the thermonuclear rate of the unmeasured ${}^{25}$Al($p,\gamma$)${}^{26}$Si reaction. Using the $\beta$ decay of ${}^{26}$P to populate the key $J^{\pi }=3^{+}$ resonance in this reaction, we report the first evidence for the observation of its exit channel via a $1741.6\pm 0.6(\text{stat})\pm 0.3(\text{syst})$ keV primary $\gamma$ ray, where the uncertainties are statistical and systematic, respectively. By combining the measured $\gamma$-ray energy and intensity with other experimental data on ${}^{26}$Si, we find the center-of-mass energy and strength of the resonance to be $E_r=414.9\pm 0.6(\text{stat})\pm 0.3(\text{syst})\pm 0.6(\text{lit.})$ keV and $\omega \gamma =23\pm 6(\text{stat}{)}_{-10}^{+11}(\text{lit.})$ meV, respectively, where the last uncertainties are from adopted literature data. We use hydrodynamic nova simulations to model ${}^{26}$Al production showing that these measurements effectively eliminate the dominant experimental nuclear-physics uncertainty and we estimate that novae may contribute up to 30% of the Galactic ${}^{26}$Al.

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• Spectral and intensity variations of Galactic 26^Al emission
• Spectroscopic factor of the 1+, 25Al(p,g)26Si resonance at Ex=5.68 MeV

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