TITLE: GCN CIRCULAR NUMBER: 25147 SUBJECT: LIGO/Virgo S190720a: Thacher Observatory follow-up observations DATE: 19/07/25 03:03:29 GMT FROM: Charles Kilpatrick at UC Santa Cruz J. Swift, Y. Yin (Thacher School Observatory), C. D. Kilpatrick, J. S. Brown, D. A. Coulter, G. Dimitriadis, R. J. Foley, T. Hung, D. O. Jones, C. Rojas-Bravo, M. R. Siebert, K. Siellez (UCSC) report on behalf of the One-Meter Two Hemisphere (1M2H) collaboration: in the process of following up the localization region of LIGO/Virgo event S190720a (GCN 25138), we observed the following fields for 300s each in r-band with the 0.7-m Thacher telescope at the Thacher School Observatory. The localization region was provided by the LIGO/Virgo collaboration in the LALinference map of July 22 17:43:30. All Thacher observations were performed on UT 2019 Jul 23. The approximate center of each image is noted in the table below, and the field of view is a 21 arcmin x 21 arcmin rectangle. We note the approximate 3-sigma limiting magnitude of each image. Comparing our images to PS1 r-band images of the same fields, we did not detect any transient sources. RA (J2000) | Dec (J2000) | MJD | Limiting Magnitude 19:45:50.18 | +35:28:46.2 | 58687.34652 | 20.4 19:55:39.26 | +37:12:37.4 | 58687.35060 | 20.1 19:54:27.91 | +37:33:24.8 | 58687.35459 | 19.8 19:52:21.53 | +38:14:58.9 | 58687.35855 | 20.2 19:55:01.25 | +37:54:12.6 | 58687.36250 | 20.0 19:56:12.58 | +37:33:26.6 | 58687.36645 | 18.8 19:53:15.86 | +37:54:13.0 | 58687.37039 | 19.0 19:57:23.21 | +37:12:40.3 | 58687.37435 | 20.1 19:56:49.44 | +36:51:54.7 | 58687.37831 | 20.5 19:50:35.76 | +38:15:01.4 | 58687.38227 | 20.7 19:51:30.55 | +37:54:15.1 | 58687.38623 | 20.6 19:52:42.91 | +37:33:27.7 | 58687.39022 | 20.6 19:53:54.65 | +37:12:41.8 | 58687.39418 | 20.6 19:55:05.59 | +36:51:56.2 | 58687.39814 | 20.3 19:48:50.04 | +38:15:02.2 | 58687.40209 | 20.2 19:49:45.19 | +37:54:15.8 | 58687.40606 | 19.7 19:50:58.03 | +37:33:29.5 | 58687.41002 | 18.5 19:52:10.22 | +37:12:43.6 | 58687.41397 | 18.9 19:53:21.70 | +36:51:57.2 | 58687.41792 | 17.1 19:54:32.47 | +36:31:12.0 | 58687.42186 | 16.9 Please direct all communication related to this circular to Charlie Kilpatrick (cdkilpat@ucsc.edu).