NEW YORK (CNNMoney.com) -- Sirius Satellite said Wednesday it added new subscribers at a rapid pace in the third quarter, helping it narrow the gap with its larger rival XM Satellite Radio.

Sirius Satellite said it added 441,101 net new subscribers during the third quarter, up 23 percent from the same period a year ago.

Sirius, whose lineup includes shock jock Howard Stern, said it had about 5.1 million total subscribers at the end of the third quarter.

XM Satellite, the largest satellite radio company with nearly 7.2 million subscribers, said it added 285,000 new net subscribers during the third quarter, less than half the number of subscribers it added this time last year.

Shares of XM Satellite (down $0.22 to $12.36, Charts) fell 3 percent, while shares of Sirius Satellite (down $0.06 to $4.01, Charts) lost about 1.5 percent in morning trading on Nasdaq.

Both companies also reaffirmed previously announced forecasts for year-end subscribers. XM said it expects to end the year with between 7.7 million and 8.2 million subscribers, and Sirius expects to reach 6.3 million subscribers by the end of the year.

XM chair upbeat