TITLE:   GCN CIRCULAR
NUMBER:  25447
SUBJECT: LIGO/Virgo S190814bv: ENGRAVE VLT/HAWK-I observations and archival detection of the CFHT candidate
DATE:    19/08/22 14:06:23 GMT
FROM:    Daniele B Malesani at DTU Space  <malesani@space.dtu.dk>

J. Japelj (Univ. of Amsterdam), Z. Jin (PMO), E. Kankare (Univ. Turku), 
E. Kool (OKC), A. J. Levan (Radboud Univ.), K. Maguire (TCD), D. B. 
Malesani (DTU Space), S. Mattila (Univ. Turku), B. Milvang-Jensen 
(DAWN/NBI), T. Reynolds (Univ. Turku), N. B. Sabha (Univ. Innsbruck), A. 
Sagues Carracedo (Stockholm Univ.), 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 host 
galaxy 2MASX J00472894-2526263 of the Canada-France-Hawaii Telescope 
(CFHT) candidate reported by Ruan et al. (GCN 25443).

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 source is detected in both 
epochs with AB magnitudes of 21.0 +- 0.1 and 20.9 +- 0.1, respectively 
(based on preliminary photometry calibrated against the 2MASS catalogue).

This field was also covered serendipitously by the ESO/VISTA survey 
telescope in the Ks band during the science verification program. The 
CFHT candidate is detected in images from 2009-10-23 and 2009-10-30. We 
measure a brightness around 0.5 mag fainter in the historic data 
compared to the HAWK-I measurement. This confirms some level of 
long-term variability, consistent with the report by Ruan et al. (GCN 
25443).

The lack of variability between the two VLT/HAWK-I images and especially 
the archival detection suggest that this object is 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).

[GCN OPS NOTE(23aug19): Per author's request, The "Drout" references
in the 1st and 3 paragraphs were changed to "Ruan".]