France Airforce over Strasbourg (MERL400)

[zillionstel]

I set up a 'Virtual Radar Server' for the first time and saw a military plane not listed on flightradar. Callsign is MERL400 and they are circling since two hours in 23000ft over Strasbourg. Does somebody know what the purpose behind this behavior is? Maybe it's something like an AWACS?

Here a picture for better visualization:
merl400___2.jpg