Macerich Company, the beleaguered mall REIT whose stock briefly soared last week before falling back down, is preparing to issue up to $500 million of new equity.One of the largest shopping center owners in the U.S., Macerich is now shopping for investors to help it meet its outstanding debt obligations, according to filings with the Securities and Exchange Commission. The Santa Monica, California-based company has a $1.5 billion line of credit that was fully drawn and comes due in July, along with $800 million in mortgages in forbearance plans.