Not a pirate station, but a worthwhile student project, and a good possible dx catch.
"Individual Broadcast radio broadcast, "Green Eyes" will air on May 7 at 16:00 on frequency 25900 kHz, will be devoted to Radio Day - anniversary of the opening Popov method transmitting information via radio waves and the invention of the world's radio."
The station is run by students of the Moscow Technical University of Communications and Informatics (MTUCI). Transmitter power is 400 watts.
They normally broadcast every Friday from 12-15 UTC on 25900, so this seems like an extra broadcast.
The process of the setting up of this station is covered in the blog "Forum for discussion of legalization Individual broadcasting" at http://tubes.radiostation.ru/arb/index.php.