TITLE: GCN CIRCULAR NUMBER: 21670 SUBJECT: LIGO/Virgo G298048: ATCA follow-up of SSS17a in NGC 4993 DATE: 17/08/24 04:30:05 GMT FROM: Tara Murphy at U of Sydney C. Lynch (University of Sydney), T. Murphy (University of Sydney), D. Kaplan (UWM), K. Bannister (CSIRO), D. Dobie (University of Sydney) on behalf of the VAST collaboration. Following Bannister et. al. (LVC GCN 21559) and Kaplan et al. (LVC GCN 21574), we observed a second epoch of NGC 4993 with the Australia Telescope Compact Array at 8.5 and 10.5 GHz. Observations started at 2017-08-20 23:31:02.9 UT and ended at 2017-08-21 11:20:00 UT with approximately 13 minutes of on-source time. We fit and subtracted a point-source at the optical position of NGC 4993 (13:09:47.71, -23:23:01.79; Skrutskie et al. 2003, 2MASS Extended Source Catalog). From this we set a 3-sigma upper limit of 135 uJy and 99 uJy on radio emission from SSS17a at 8.5 and 10.5 GHz respectively. Subsequent epochs are planned. Thank you to CSIRO staff for supporting these observations.