Letter to the Editor

Line shape diagnostics of Galactic Al

¹ Max-Planck-Institut für extraterrestrische Physik, Postfach 1312, 85741 Garching, Germany
² Department of Physics & Astronomy, Clemson University, Clemson, SC 29634-0978, USA

Corresponding author: K. Kretschmer, kkr@mpe.mpg.de

Received: 7 July 2003
Accepted: 6 November 2003

Abstract

The shape of the gamma-ray line from radioactive , 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  keV FWHM, the GRIS 1996 value of  keV FWHM, and the recent RHESSI value of  keV FWHM, suggesting either “cold”, “hot”, or “warm”  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  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  velocity through extreme assumptions about grain transport of  or huge interstellar cavities, our results suggest that standard  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 .