A benchmark index of Indian equities markets, the 30-scrip Sensitive Index (Sensex), on Thursday surged 507.15 points or 1.97 percent during the afternoon session.The wider 50-scrip Nifty of the National Stock Exchange (NSE) also gained 151.90 points or 1.95 percent and was trading at 7,943.75 points.The Sensex of the S&P Bombay Stock Exchange (BSE), which opened at 26,137.03 points, was trading at 26,221.81 points (at 2.11 p.m.) in the afternoon session -- up 507.15 points or 1.97 percent from the previous day's close at 25,714.66 points.The Sensex touched a high of 26,256.44 points and a low of 25,943.75 points in the trade so far.