Per John Blake on Twitter, the Rangers have activated pitcher Alexi Ogando from the 15 day disabled list.
The move appears to be essentially procedural in nature, as Ogando is not expected to be ready for game action for a few more days, at least. However, with rosters having expanded, there is no reason not to add Ogando to the active roster at this point.
Ogando has only made 15 starts and thrown 80.1 innings this season, as he has been on the disabled list three different times. There is no indication as of yet whether Ogando will re-join the rotation when he's ready to pitch again, or if he will go to the bullpen. Travis Blackley is currently acting as the team's #5 starter, and Nick Tepesch, who spent the first half of the season in the rotation, was activated from the disabled list on September 1 and is also a rotation option.