** Rosenblatt Securities upgrades audio entertainment firm SiriusXM SIRI.O to "buy" from "neutral"
** Raises PT to $46 from $24, implying a 63.9% upside to stock's last close
** Argues that the YouTube deal announced on Wednesday could be a "huge unlock of value" for the stock
** Under the deal, Alphabet's GOOGL.O YouTube will become SIRI's exclusive audio advertising sales partner in the U.S.; new buying option expected to be launched this fall
** Average rating of 16 analysts is "hold;" their median PT is $24 - data compiled by LSEG
** Stock has risen 40.8% YTD
(Reporting by Anhata Rooprai in Bengaluru)
((Anhata.Rooprai@thomsonreuters.com))