Based on observations with INTEGRAL, an ESA project with instruments and science data centre funded by ESA member states (especially the PI countries: Denmark, France, Germany, Italy, Switzerland, Spain), Czech Republic and Poland, and with the participation of Russia and the USA.

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... $\Gamma = 1.8 {+1.5 \atop -0.6}$

Errors are 2 $\sigma$ errors throughout the paper.

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