Athenahealth on Monday announced it had received an unsolicited cash offer from Elliott Management, the hedge fund of activist investor Paul Singer, to buy the health information technology company for roughly $6.9 billion. Elliott Management offered $160 per share in cash, which represented a 27 percent premium on market price of athenahealth stock at the time. Athenahealth provides administrative services for record-keeping, revenue tracking, patient engagement, care coordination and other health care-related services. It opened offices in Belfast in 2008 and is now among the three largest employers in Waldo County, with between 800 and 1,000 workers. The company restructured earlier this year in response to pressure from Singer and Elliott Management, which owns an 8.9 percent share of the athenahealth.