TITLE: GCN CIRCULAR NUMBER: 17002 SUBJECT: GRB 141031A: VLT/X-shooter optical observations DATE: 14/10/31 18:46:44 GMT FROM: Daniele Malesani at Dark Cosmology Centre, Niels Bohr Inst D. Xu (DARK/NBI), A. de Ugarte Postigo (IAA/CSIC and DARK/NBI), S. D. Vergani (CNRS/GEPI), A. J. Levan (Univ. Warwick), J. P. U. Fynbo (DARK/NBI), N. R. Tanvir (Univ. Leicester), B. Milvang-Jensen (DARK/NBI), D. Malesani (DARK/NBI), K. Wiersema (Univ. Leicester), report on behalf of a larger collaboration: We observed the field of GRB 141031A (Gompertz et al., GCN 16995) using the VLT X-shooter spectrograph, using the robotic rapid response mode (RRM). In a 15-s acquisition image, taken at 7:41:19 UT (22.8 min after the GRB1), we identify three objects consistent with, or in the close vicinity of, the currently available XRT error circle (1.4" error radius; Evans et al., GCN 16997 and http://www.swift.ac.uk/xrt_positions/). Their coordinates are (all J2000): A) RA = 08:34:26.11 Dec = -59:10:04.2 B) RA = 08:34:25.73 Dec = -59:10:04.8 C) RA = 08:34:26.05 Dec = -59:10:04.9 Sources A and C are partially blended. Source B is the one detected by GROND (GCN 16996), looks extended in our data (under 0.6" seeing), and is now formally outside the latest XRT position (2.7"+-1.4" away). The limiting magnitude of the image is R ~ 21.7. A finding chart is available at http://www.astro.ku.dk/~malesani/GRB/141031A/finder_XS.jpg A later image (30 s exposure) was taken 104.5 min after the GRB. Image subtraction reveals no obvious variation of any of the sources, despite the significant time difference between the two epochs (factor of 4.5 in time since GRB). A spectrum was secured of source A, covering the wavelength range 3000-25,000 AA. Several features are observed in absorption, including the Balmer series from Halpha to H15, and Ca H and K, at z = 0.0013. Such redshift is consistent with the Milky Way or the Local Group, though the corresponding velocity (390 km/s) is substantial for an origin in the MW disk. Our slit did not cover, unfortunately, objects B and C. Further analysis is in progress, and we invite further monitoring of these object to single out variability. We acknowldge excellent support from the observing staff in Paranal, in particular Juan Carlos Munoz-Mateos, Francisco Caceres, Rodrigo Romero, and Steffen Mieske.