TITLE: GCN CIRCULAR NUMBER: 26473 SUBJECT: LIGO/Virgo S191216ap: No significant counterpart candidates in SAGUARO observations DATE: 19/12/17 14:13:53 GMT FROM: Michael J. Lundquist at University of Arizona Michael J. Lundquist, David J. Sand (UA), Wen-fai Fong, Jillian Rastinejad, Kerry Paterson (Northwestern), Jennifer Andrews (UA), Sam Wyatt (UA), Eric Christensen, Alex Gibbs, Frank Shelly, report on behalf of the SAGUARO collaboration: We initiated observations of 24 fields (each 5 deg^2, totalling 120 deg^2) within the LVC localization region for the GW trigger S191216ap (LVC Circ 26454) starting on 2019-12-17 at 1:25 UT (3.9 hours after the GW trigger) with the 1.5m Catalina Sky Survey (CSS) telescope on Mt. Lemmon, AZ. Below are the field centers observed. RA Dec 321.5850 1.10417 321.3495 3.3125 321.3495 5.52081 321.1110 7.72917 321.1110 9.93747 320.8695 12.1458 323.1060 12.1458 320.3775 14.3541 322.6410 14.3541 320.1255 16.5625 322.4055 16.5625 321.9225 18.7708 319.6155 18.7708 321.4290 20.9792 319.0905 20.9792 320.9205 23.1875 318.5520 23.1875 320.1330 25.3958 317.7180 25.3958 319.3155 27.6042 316.8495 27.6042 318.4605 29.8125 317.5710 32.0208 316.6425 34.2291 Overall image quality was poor. We perform real-time processing and image subtraction (described in Lundquist et al. 2019, ApJL, 881, 2). After discarding known moving objects, stellar sources and known transients (cross-correlating with the Transient Name Server and the ZTF alert stream), we find no significant candidates with S/N>5, although a more detailed analysis is ongoing. We have posted our pointings to the Treasure Map, and encourage others to do the same: http://treasuremap.space/alerts?graceids=S191216ap SAGUARO is supported by the National Science Foundation under Award Nos. AST-1909358 and AST-1908972.