TITLE: GCN CIRCULAR NUMBER: 11221 SUBJECT: GRB 100901A: Possible WSRT Radio Detection DATE: 10/09/06 04:36:07 GMT FROM: Alexander van der Horst at NASA/MSFC A.J. van der Horst (NASA/MSFC/ORAU), K. Wiersema (U of Leicester), A.P. Kamble, R.A.M.J. Wijers, E. Rol (U of Amsterdam) and C. Kouveliotou (NASA/MSFC) report on behalf of a large collaboration: "We observed the position of the GRB 100901A afterglow at 4.9 GHz with the Westerbork Synthesis Radio Telescope at September 3 20.35 UT to September 4 08.50 UT, i.e. 2.29 - 2.79 days after the burst (GCN 11159). We detect a radio source at the position of the X-ray and UV/optical counterpart (GCN 11195) at the 4-sigma level, with a flux density of 134 +/- 33 microJy. We would like to thank the WSRT staff for scheduling and obtaining these observations."