Burlington software company Exa begins trading
Burlington software maker Exa Corp. rang the opening bell on the Nasdaq Thursday morning and became the first company since Facebook Inc. to debut on the exchange. Exa priced its initial public offering on Wednesday night at $10 a share, below its range of $11 to $13, and raised $62.5 million. It began trading Thursday morning. Another Massachusetts company, Waltham biotech firm Tesaro Inc., priced its initial public offering on Thursday and raised $81 million.