PSEC was removed from the S&P 600 index today. So rather then sell in the open market at a discount, they pre-arranged trades with other funds. Index funds that held this has no choice to sell. What they did was get on the phone and make arranged deals with other funds. (I know that to be true becasue I read it on the Web. LOL)
The total volume today, including after hours, is over 68 million shares; that's 15 times the 3-month daily average. Almost all of this was pre-arranged trades -- note the 16 million at 4:00 pm and the 9 million at 4:43 pm; these large trades did not have any affect on the market price.