Without a traceflag, there's nothing written into the SQL errorlog.
The deadlock error is sev 16, not enough to be logged. You can set up an agent alert for it or, since you're on SQL 2008 you can poll the system health extended events session and get the entire deadlock graph.
The system health session is much like the default trace, it's a circular file so any deadlocks caught aren't kept forever.
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