TITLE: GCN CIRCULAR NUMBER: 25526 SUBJECT: LIGO/Virgo S190814bv: no variation of DESGW candidates AT 2019onj and AT 2019okr from ENGRAVE VLT/HAWK-I observations, and archival detection DATE: 19/08/28 19:26:10 GMT FROM: Susanna Vergani at INAF/Brera J. Japelj (Univ. of Amsterdam), E. Kankare (Univ. Turku), E. Kool (OKC), A. J. Levan (Radboud Univ.), K. Maguire (Trinity College Dublin), D. B. Malesani (DTU Space), S. Mattila (Univ. Turku), B. Milvang-Jensen (DAWN/NBI), T. Reynolds (Univ. Turku), N.B. Sabha (Univ. Innsbruck), S. D. Vergani (Paris Observatory-CNRS) report on behalf of the ENGRAVE collaboration: ENGRAVE targeted 9 fields containing 17 high-probability host galaxies for S190814bv, based on the LALInference skymap (LIGO Scientific Collaboration and Virgo Collaboration, GCN 25333), with deep VLT/HAWK-I imaging over two epochs in a search for intrinsically faint, near-infrared transient sources. As part of this search, we observed the field of two candidates, AT 2019onj and AT 2019okr, reported by Soares-Santos et al. (GCN 25486). The observations were conducted between 06:55 and 07:14 UT on 2019-08-16 and a second epoch between 04:32 and 04:50 UT on 2019-08-21, approximately 1.4 and 6.3 d after S190814bv, respectively (600 s exposure per epoch in the Ks filter). The sources are detected in both epochs with magnitudes: Name dT Ks mag AT 2019onj 1.4 d 19.20 +- 0.03 AT 2019onj 6.3 d 19.15 +- 0.02 AT 2019okr 1.4 d 19.55 +- 0.03 AT 2019okr 6.3 d 19.54 +- 0.03 The magnitudes (in the Vega system, not corrected for extinction) are based on preliminary photometry calibrated against a single 2MASS star, and the absolute calibration has an extra error by 0.05 mag. No significant variability can be measured between our HAWK-I observations. This field was also covered serendipitously by the ESO/VISTA survey telescope in the Ks band during its science verification program. Both objects are detected in images from 2009-10-23 and 2009-10-30, and both are fainter than in the HAWK-I images (by 0.68+-0.18 and 0.83 +- 0.26 mag for AT 2019onj and AT 2019okr, respectively). The large uncertainty is entirely due to the low S/N of the archival VISTA data. The lack of variability between the VLT/HAWK-I epochs and especially the archival detections suggest that AT2019onj and AT2019okr are unrelated to S190814bv. We acknowledge the ESO observing staff at Paranal, in particular S. Brillant, J. Corral-Santana, B. Haussler, C. Opitom, F. J. Selman, and T. Szeifert. Based on observations collected by the ENGRAVE collaboration at the European Southern Observatory under ESO program 0103.D-0722 (for further information on ENGRAVE see http://www.engrave-eso.org/). The VISTA data were secured under science verification program 60.A-9285(A). We acknowledge valuable help with the archival VISTA data by Carlos Gonzalez-Fernandez (CASU / IoA Cambridge).