SX-BGK is a Boeing 737-3Y0 (c/n 24679 / 1897), seen here at Paris-CDG on 24Jun01.
More on SX-BGK on Airliners.net.
Cronus Airlines was acquired by Aegean Airlines in 2001, traded temporarily as Aegean Cronus Airlines, then merged into Aegean AL.
The fleetlist in 2000 consisted of 737-300s (SX-BBT, SX-BBU, SX-BGI, SX-BGK) and 737-400s (SX-BHG, SX-BGJ); a 737-700 was on order for delivery in 2001.
Cronus Airlines on Airliners.netSource: AeroTransport Data Bank