** Shares of U.S. refiner CVR Energy CVI.N up 1.8% at $18.65
** Billionaire activist Carl Icahn's investment firm Icahn Enterprises IEP.O unveils slightly sweetened public bid to boost its stake in the refiner to 84%
** IEP launches offer to buy 17.8 million additional shares in the refining firm at $18.25 per share
** IEP already owns 66.3% of the refiner
** Including session's gain, stock is down 38.5% YTD
(Reporting by Sourasis Bose in Bengaluru)
((Sourasis.bose@thomsonreuters.com))