GCN Circular 21987
John R. Thorstensen (Dartmouth) and Jules P. Halpern (Columbia) report: Automated analysis of Swift XRT data (GCN #21986) on Fermi-LAT GRB 171010A (GCN #21985) reports a fading X-ray source at: (J2000.0) 04:26:19.44 -10:27:47.1 +/- 1.4" We pointed the 1.3m McGraw-Hill telescope of the MDM Observatory at this location beginning on 2017 October 11 08:31 UT, 13.5 hr after the burst, and obtained images in the Cousins R filter that show a new object at: (J2000.0) 04:26:19.48 -10:27:46.2 +/- 0.4" with position referenced to the PPMXL catalog. In comparison with nearby stars with r magnitudes from Pan-STARRS, we estimate r = 18.0 at 08:31 UT. Continuing photometry shows that the OT faded from r = 18.05 to 18.38 between 8:55 UT and 10:28 UT. There is also a faint galaxy at this position on the digitized POSS II and in Pan-STARRS, but bright moon now makes it difficult to detect in our images. The Pan-STARRS position of this possible host galaxy is: (J2000.0) 04:26:19.56 -10:27:45.8 Using the 2.4m Hiltner telescope with Modspec, we obtained 17x12 minutes spectra of the OT covering the wavelength range 4400-7500 A at 4 A resolution, which when summed show a featureless continuum with a signal-to-noise ratio of about 50 per 2 A pixel.