The Austrian prosecutors' office has opened an investigation into Wien Energie, the Vienna power company that recently received state help with surging margin calls but whose trading in futures markets has been questioned by the finance minister. As power futures rocketed to new records above 1,000 euros ($1,000) per megawatt hour at the end of last month, the city-owned company and the city government appealed to the federal government for help in dealing with the cost of margin calls - amounts required for accounts to keep trading.