Picture of the Month 

January 2006

INTEGRAL Picture Of the Month (POM): Galactic Rotation seen in the 26 Al line by INTEGRAL

Galactic Rotation seen in the 26Al line by INTEGRAL

In a recent article in Nature (published January 5 2006) Diehl et al. present observations on the Galactic Centre obtained with the SPI instrument onboard INTEGRAL. The exposure time at the Galactic Center is 4 Ms.

The picture shows at the left the line profiles obtained at different locations; a clear shift in the line centroid in the top and bottom panels compared to the center panel (l = 0) is visible. Detailed modelling shows that the shift is fully consistent with the Doppler shift of the line energy (1809 keV) expected from the galactic rotation. The map on the right shows this expectaction based on modelling the Galactic rotation curve and a 3-dimensional distribution of 26Al sources. The observed line shift is less than 0.5 keV, demonstrating the superb quality of SPI's spectral resolution capabilities. The dominant sources of 26Al emission are massive stars. This observation shows that 26Al emission is truly global, as we see the entire amount of it throughout our Galaxy and co-rotate with the Galaxy.

From this observation Diehl et al. determine a present-day equilibrium mass of 2.8 +/- 0.8 solar masses of 26Al. In addition, this observation allows to independently estimate the frequency of core-collapse supernovae in our Galaxy to be 1.9 +/- 1.1 events per century.

Credits: R. Diehl (MPE, Garching Germany)

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