Line shape diagnostics of Galactic 26Al
Abstract
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 106 y after its ejection into the interstellar medium from its nucleosynthesis source. Three measurements of the line width exist: HEAO-C's 1982 value of (0+3) keV FWHM, the GRIS 1996 value of (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-Rayet winds, and predict a value below 1 keV (FWHM) with plausible assumptions about 26Al 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 of 26Al or huge interstellar cavities, our results suggest that standard 26Al ejection models produce a line on the narrow side of what is observed by RHESSI and INTEGRAL. Improved INTEGRAL and RHESSI spatially-resolved line width measurements should help to disentangle the effects of Galactic rotation from the ISM trajectories of 26Al.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- December 2003
- DOI:
- 10.1051/0004-6361:20034604
- arXiv:
- arXiv:astro-ph/0311218
- Bibcode:
- 2003A&A...412L..47K
- Keywords:
-
- nuclear reactions;
- nucleosynthesis;
- abundances;
- gamma rays: observations;
- supernovae: general;
- ISM: supernova remnants;
- stars: formation;
- Astrophysics
- E-Print:
- 5 pages, 4 figures, accepted for publication in A&