The established ratio for the merger is 4.6 shares of SIRI stock for every share of XM stock. The ratio that these equities have been trading at typically runs between 3.9 and 4.1, showing about a 20% discount if you buy XM shares in belief that the merger will pass.
At some point, the arbitrage of this trade will come into play. Particularly if sentiment about merger approval is high. The question is when the Arb's will decide is the right time to jump in, and how will that effect the stock price.
Are people using this as a strategy to by XMSR shares when the ratio falls below 4 to 1? It will be an interesting summer.