TITLE: GCN CIRCULAR NUMBER: 22187 SUBJECT: GRB 171205A: NOEMA detection of a bright mm afterglow DATE: 17/12/06 10:26:44 GMT FROM: Antonio de Ugarte Postigo at IAA-CSIC A. de Ugarte Postigo (HETH/IAA-CSIC, DARK/NBI), S. Schulze (Weizmann), M. Bremer, M. Krips (IRAM), C.C. Thoene, L. Izzo, D.A. Kann, Z. Cano, K. Bensch (HETH/IAA-CSIC), S. Martin Ruiz, I. de Gregorio (ALMA), S. Kim (PUC), R. Sánchez-Ramirez (INAF-IAPS), D. Malesani (DARK/NBI) report: We observed the afterglow of GRB 171205A with NOEMA at 150GHz and 90GHz starting at 3:30 UT on the 6th of December (20.2 hrs after the GRB onset). We detect a bright afterglow in 150GHz with a preliminary flux density estimate of 35-40 mJy. The coordinates of the detected source are (J2000 +/- 0.05"): R.A.: 11:09:39.52 Dec.: -12:35:18.34 We note that if the flux density is confirmed, it would be the second brightest GRB ever detected in mm/submm wavelengths, after GRB 030329 (for a review on mm/submm data of GRBs see de Ugarte Postigo et al. 2012). Further follow-up observations are encouraged.