Letter to the Editor

Detection of γ-ray lines from interstellar Fe by the high resolution spectrometer SPI

¹ Centre d'Étude Spatiale des Rayonnements, BP 4346, 31028 Toulouse Cedex 4, France e-mail: Mike.Harris@cesr.fr
² IASF, via E. Bassini 15, 20133 Milano, Italy
³ Max-Planck-Institut für extraterrestrische Physik, Postfach 1603, 85740 Garching, Germany
⁴ DSM/DAPNIA/SAp, CEA Saclay, 91191 Gif-sur-Yvette, France

Received: 1 February 2005
Accepted: 23 February 2005

Abstract

It is believed that core-collapse supernovae (CCSN), occurring at a rate ~once per century, have seeded the interstellar medium with long-lived radioisotopes such as ⁶⁰Fe (half-life 1.5 Myr), which can be detected by the γ-rays emitted when they β-decay. Here we report the detection of the ⁶⁰Fe decay lines at 1173 keV and 1333 keV with fluxes 3.7 ± 1.1   per line, in spectra taken by the SPI spectrometer on board INTEGRAL during its first year. The same analysis applied to the 1809 keV line of ²⁶Al yielded a line flux ratio ⁶⁰Fe/²⁶Al = 0.11 ± 0.03. This supports the hypothesis that there is an extra source of ²⁶Al in addition to CCSN.