By Vidya Ranganathan and Kevin Buckland SINGAPORE (Reuters) – The Japanese yen made a thumping 4 yen jump for a second straight session on Monday on suspected early intervention by the Bank of Japan, but struggled to hold its gains against a robust U.S. dollar. The yen hit a low of 149.70 per dollar in early deals before being swept to a high of 145.28 within minutes in a move that suggested the BOJ had stepped in for a second successive day. The currency, however, dropped back to near 148 soon. “It’s blindingly obvious that the BOJ is intervening,” said Ray Attrill, head of FX strategy at Nat…