Strings in AdS_3 and the SL(2,R) WZW Model. Part 2: Euclidean Black Hole
  We consider the one-loop partition function for Euclidean BTZ black hole backgrounds or equivalently thermal AdS_3 backgrounds which are quotients of H_3 (Euclidean AdS_3). The one-loop partition function is modular invariant and we can read off the spectrum which is consistent to that found in hep-th/0001053. We see long strings and discrete states in agreement with the expectations. 
Juan Maldacena, Hirosi Ooguri, and John Son