Astronomy & Astrophysics
The shape of the gamma-ray line from radioactive 26Al, at 1808.7 keV energy in the frame of the decaying isotope,is determined by its kinematics when it decays, typically 106y after its ejection into the interstellar medium from its nucleosyn-thesis source. Three measurements of the line width exist: HEAO-C’s 1982 value of (0 + 3) keV FWHM, the GRIS 1996 valueof (5. 4 ± 1. 3) keV FWHM, and the recent RHESSI value of (2. 0 ± 0. 8) keV FWHM, suggesting either “cold”, “hot”, or “warm”26Al in the ISM. We model the line width as expected from Galactic rotation, expanding supernova ejecta, and/or Wolf-Rayetwinds, and predict a value below 1 keV (FWHM) with plausible assumptions about26Al initial velocities and expansion history.Even though the recent RHESSI measurement reduces the need to explain a broad line corresponding to 540 km s− 1 mean 26Al velocity through extreme assumptions about grain transport of26Al or huge interstellar cavities, our results suggest thatstandard26Al ejection models produce a line on the narrow side of what is observed by RHESSI and INTEGRAL. ImprovedINTEGRAL and RHESSI spatially-resolved line width measurements should help to disentangle the eﬀ ects of Galactic rotationfrom the ISM trajectories of 26Al
Please use publisher's recommended citation.