GCN Circular 21816
S. M. Adams, M. M. Kasliwal, N. Blagorodnova (Caltech) report on behalf of a larger GROWTH (Global Relay of Observatories Watching Transients Happen) collaboration We registered our HST F336W image (PI Kasliwal) with the Gaia astrometric catalog to derive a more precise position of SSS17a (Coulter et al. LVC GCN 21529). We find a position of 13:09:48.071 -23:22:53.37 with astrometric residuals of 0.05". This new position is consistent with the position of the radio source reported in companion GCNs by Corsi et al. LVC GCN 21815 and Mooley et al. LVC GCN 21814.