TITLE: GCN CIRCULAR NUMBER: 6985 SUBJECT: GRB 071021: R-band detection and analysis DATE: 07/10/24 20:23:32 GMT FROM: Silvia Piranomonte at OAR S. Piranomonte (INAF/OAR), P. D'Avanzo (INAF/OABr), D. Malesani (DARK), A. Fernandez-Soto ( U.Valencia), G. Tagliaferri (INAF/OABr), G. Chincarini (U.Bicocca), S. Covino (INAF/OABr), F. Fiore (INAF/OAR), D. Fugazza (INAF/OABr), L. Stella (INAF/OAR), report on behalf of the MISTICI collaboration: We observed the field of GRB 071021 (Sakamoto et al., GCN 6958) with the 8.2m VLT+FORS2 equipped with the R filter (effective wavelength: 6550 A; FWHM: 1650 A). An eight-minute exposure was obtained on Oct 22.06688 , and a second, thirty-minute exposure, on Oct 22.99604. A weak source is detected in both images at the position of the candidate afterglow provided by Castro-Tirado et al. (GCNs 6968, 6971). The object has not faded significantly between both epochs, although the very low S/N (~2) in the first image does not allow for a strong statement regarding its variability. Combining our own data and all the available optical-NIR data (GCNs 6962, 6973, 6974, 6975, 6976, 6980, 6983) we have measured a photometric redshift z~5, but with a 2-sigma confidence interval that includes all values in the z=[0 ... 5.5] range. An alternative explanation for all the available data is that of a strongly reddened afterglow (detected as a fading source in the H- and K-band images), having taken place in a galaxy at a significantly lower redshift (detected in our deeper, bluer, R- and z-band images). This model should be checked via spectroscopy of the putative host galaxy. Our R-band images and the results of the preliminary photometric redshift analysis are posted at: http://ayalga.uv.es/~fsoto/grb/grb071021/ We acknowledge excellent support from the ESO staff, in particular Emanuela Pompei and Hugues Sana. This message may be cited. ------------------------------------------------- This mail sent through IMP: http://horde.org/imp/