The upgrade in rating from Underweight to Equal-Weight by a major financial institution like Barclays indicates a positive reassessment of SL Green Realty's market position and future prospects. The significant increase in the price target from $35 to $48 further underscores the optimism about the company's potential for growth or recovery. This kind of analyst action typically leads to increased investor confidence and can drive up the stock price in the short term as market participants adjust their expectations based on the new information.