TITLE: GCN CIRCULAR NUMBER: 8501 SUBJECT: GRB 081109: REM NIR afterglow detection DATE: 08/11/09 09:54:49 GMT FROM: Stefano Covino at Brera Astronomical Observatory P. D'Avanzo, S. Covino, L.A. Antonelli, D. Malesani, D. Fugazza, L. Calzoletti, S. Campana, G. Chincarini, M.L. Conciatore, S. Cutini, V. D'Elia, F. D'Alessio, F. Fiore, P. Goldoni, D. Guetta, C. Guidorzi, G.L. Israel, E. Maiorano, N. Masetti, A. Melandri, E.J.A. Meurs, L. Nicastro, E. Palazzi, E. Pian, S. Piranomonte, L. Stella, G. Stratta, G. Tagliaferri, G. Tosti, V. Testa, S.D. Vergani, F. Vitali report on behalf of the REM team: The robotic 60-cm REM telescope located at La Silla (Chile) observed automatically the field of the GRB 081109 (Immler et al. GCN 8500) on Nov 09 starting about 52 s after the burst. Observations were carried out at high airmass (~ 6). We clearly detect an object in our first K-band image inside the XRT error box (Immler et al. GCN 8500) at the following coordinates (J2000): R.A. = 22:03:09.72 Dec = -54:42:39.5 with an uncertainty of 1.0". The object is not visible in the single RJH images taken approximately at the same epoch. Coadding all the available RJH images taken around the same epoch we obtain the following results: Mean_obs texp #frames_coadd Filter Mag Nov 09.30604 UT 780 s 11 R > 16.5 (3sigma) Nov 09.30707 UT 65 s 4 J > 15.8 (3sigma) Nov 09.29936 UT 75 s 7 H 15.47 ± 0.26 Nov 09.30145 UT 10 s 1 K 14.51 ± 0.27 The object subsequently brightened, reaching K = 14.27 ± 0.16 on Nov 09.30612 UT. No object is detected at this position in the 2MASS and USNO catalogs. We propose this is the NIR afterglow of GRB 081109. We cannot indeed exclude the possibility that the lack of detection blueward of the H band is due to an high-redshift nature of this event. We note, however, that the large airmass badly affects the images in the J and R bands, so that our limits are not very constraining Further deep optical/NIR observations are encouraged.