How the world's biggest bond managers are investing in a tumultuous market

By Suzanne McGeeA tumultuous ride for bonds this year has left Vanguard's senior bond fund manager Arvind Narayan with one unequivocal message: "This is not the time to be a hero."Narayan, who co-heads a $55 billion bond fund, is one of eight of the largest US bond fund managers with whom Reuters s…