TITLE:   GCN CIRCULAR
NUMBER:  21574
SUBJECT: LIGO/Virgo G298048: ATCA upper limits on radio emission from optical source SSS17a in NGC 4993 
DATE:    17/08/18 20:19:00 GMT
FROM:    David Kaplan at UW-Milwaukee  <kaplan@uwm.edu>

D. Kaplan (UWM), T. Murphy (University of Sydney), K. Bannister (CSIRO), C. Lynch (University of Sydney), D. Dobie (University of Sydney) on behalf of the VAST collaboration.

Following Bannister et al. (LVC GCN 21559), who reported ATCA detections of a radio source consistent with the position of NGC 4993 that is also seen with the VLA (Alexander et al. LVC GCN 21548), we present upper limits to the radio emission of any source at the position of the potential optical counterpart, SSS17a (Coulter et al., LVC GCN 21529).

We fit and subtracted a point-source at the optical position of NGC 4993 (13:09:47.706, -23:23:01.79; Skrutskie et al. 2003, 2MASS Extended Source Catalog).  The flux densities were consistent with the values reported by Bannister et al. (LVC GCN 21559).  We then measured the rms noise at the position of SSS17a as well as 3 other source-free positions nearby.  In all cases there was no detectable emission at the position of SSS17a (9.9 arcsec away), and the noise was essentially identical across all positions.  

Assuming that all of the emission originates with the center of NGC 4993, our flux density for the galaxy and 3-sigma upper limits to emission at the position of SSS17a are:

Frequency	NGC 4993 Flux Density	3-sigma Limit for SSS17a
8.5 GHz: 	0.66 mJy			120 uJy
10.5 GHz:	0.54 mJy			150 uJy
16.7 GHz: 	0.42 mJy			130 uJy
21.2 GHz: 	0.34 mJy			140 uJy

Thank you to CSIRO staff for supporting these observations.