* Nikkei and Topix both up 0.6 pct * Sony rises after hedge fund ups stake, presses spin-off By Dominic Lau TOKYO, June 18 (Reuters) - Japan's Nikkei rose on Tuesday, heading for a third straight day of gains, which will mark its longest winning run since a sharp selloff on May 23, underpinned by hopes the Federal Reserve will reinforce its commitment to support the U.S. economy. Sony Corp climbed 3.6 percent after New York-based hedge fund company Third Point said it had raised its stake in the Japanese firm and asked for an opportunity to present its proposal for a partial spin-off of Sony's entertainment unit to the board. It was the most traded stock on the main board by turnover. The Nikkei advanced 0.6 percent to 13,107.03, breaking above the bottom of the Ichimoku cloud in a bullish sign. It climbed 2.7 percent on Monday, lifting the index out of bear market territory. "The yen move is obviously driving the yen-sensitives higher from their low positions ... It's a nice pick-up in volume versus yesterday but nothing really fundamental," a senior trader at a foreign brokerage said. The yen was last traded at 94.79 yen to the dollar on Tuesday, down from the previous session's high of 94.08, giving exporters some support. Toyota Motor Corp put on 1.6 percent and was the second-most traded, while Subaru maker Fuji Heavy Industries added 1.9 percent and Mazda Motor gained 1.4 percent. The broader Topix index gained 0.6 percent to 1,091.18, ahead of a two-day Fed meeting that will begin on Tuesday. Many investors have been cutting their long Japanese equities and short yen positions on concerns that the Fed will scale back its stimulus and after the Nikkei had rallied more than 80 percent from mid-November to its 5-1/2 year peak hit on May 23. Since then, trading in Japanese equities has been extremely volatile. Disappointment over a growth strategy unveiled by the Japanese government recently and worries over slowing growth in China have also contributed to the market tumult. Underscoring the volatility, since May 23 the Nikkei has had 15 sessions where intraday swings exceeded 2.5 percent, compared with 16 such trading days for the year up to May 22 and four such days in the whole of 2012. The U.S. S&P 500 only has had one such trading day in 2013, and the Euro STOXX 50 index has 11. The benchmark Nikkei has fallen 17.6 percent since that mulityear high on May 23, but is still up 6 percent since April 4, when the Bank of Japan unveiled sweeping stimulus measures and has risen 26 percent this year.