State Sen. Scott Brown (R) said Thursday that he had raised over $600,000 for his long-shot Massachusetts Senate campaign in the month of December.

That more than doubles what Brown has reported in receipts through Nov. 18. But it is well behind the fundraising pace of state Attorney General Martha Coakley (D), the favorite in the race, who announced raising more than $1 million in the reporting period that began on November 20th through the end of December. That brings her total fundraising number since the beginning of the Senate campaign to more than $5.2 million.

The Brown campaign also released plans Thursday for a “moneybomb” scheduled for Jan. 11, eight days before the Jan. 19 special election. The fundraising technique, pioneered by the presidential campaign of Rep. Ron Paul (R-Texas), encourages donors to coordinate their giving on a certain day.