Days after Gilead Sciences ($GILD) spurred a wave of buyout rumors with its effort to bring in $10 billion, Biogen ($BIIB) laid out plans to raise $6 billion of its own, providing few details as it looks to bolster its cash position. The Cambridge, MA, drugmaker priced four series of senior notes, maturing between 2020 and 2045, in an offering expected to close next week. Some of the money will go toward a previously announced share repurchase program, the company said, with the rest tabbed for the vague "working capital and other general corporate purposes." More