LIGO/Virgo S190720a: Thacher Observatory follow-up observations

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).