TITLE:   GCN CIRCULAR
NUMBER:  21551
SUBJECT: LIGO/Virgo G298048: Magellan g-band Imaging of the Potential Optical Counterpart Associated with NGC 4993
DATE:    17/08/18 07:54:23 GMT
FROM:    Mansi M. Kasliwal at Caltech  <mansi@astro.caltech.edu>

J. D. Simon, B. J. Shappee, M. R. Drout (Carnegie), D. A. Coulter, R. J.
Foley, C. D. Kilpatrick, M. R. Siebert (UCSC), K. Boutsia, J. Bravo, G.
Prieto (Las Campanas Observatory), and A. L. Piro (Carnegie)

On 2017 Aug 18.01 UT we obtained g-band images of the transient source
SSS17a (RA = 13:09:48.09 DECL. = -23:22:53.35, Coulter et al. 2017; GCN
21529) possibly associated with LIGO/Virgo G298048, with LDSS-3 on the 6.5m
Magellan-Clay telescope at Las Campanas Observatory.  We measure a
provisional magnitude of g = 17.2 +/- 0.1, consistent with the blue color
reported spectroscopically by Drout et al. 2017 (GCN 21547) and at redder
wavelengths by Nicholl et al. 2017 (GCN 21541).  We also note a tentative
detection of a slight decrease in brightness over three exposures spanning
12 minutes.  Further analysis is ongoing.