INTEGRAL SPI observes the gamma-ray lines of interstellar 60Fe
The SPI instrument on board INTEGRAL has observed the 60Fe lines (at
1173 and 1333 keV) from the inner galaxy. The picture shows the
combined 60Fe signal from the two lines. The line flux is 3.7 ± 1.1 x
10^5 cm^{-2} s^{-1} per line. The origin of the iron line is believed
to be core-collapse supernovae which seed the interstellar medium with
isotopes such as 60Fe. From other SPI measurements of the 26Al line
the ratio 60Fe/26Al = 0.11 ±0.03 is derived, which is substantially
smaller than predictions (0.40) for massive stars. This ratio supports
the idea that there is an extra source of 26Al in addition to the
core-collapse supernovae.
