Technically, I guess The Fed (the central bank of the US) doesn't own any gold (source):
But the Fed says it stores gold owned by "other central banks", so some central banks must own gold.The New York Fed’s gold vault is on the basement floor of its main office building in Manhattan. ...
None of the gold stored in the vault belongs to the New York Fed or the Federal Reserve System. The New York Fed acts as the guardian and custodian of the gold on behalf of account holders, which include the U.S. government, foreign governments, other central banks, and official international organizations.
BTW, that was a very interesting graph. But if it's a model of what will happen in the coming crisis, we can expect half a year of bargain gold prices before it jumps right back and resumes its ascent.