F. A. Harrison, K. Forster, J. Garcia, B. W. Grefenstette, M. Heida, M. M.
Kasliwal, K. K. Madsen, H. Miyasaka, S. Pike, V. Rana, Y. Xu (Caltech)
We obtained X-ray imaging of the optical counterpart of SSS17a (Coulter et
al.; GCN21529), the candidate optical counterpart of G298048 (LVC; GCN
21509) in the 3 ��� 79 keV band with NuSTAR. Observations began at
2017-08-18T05:26:09 UT and ended at 2017-08-18T19:46:09, with a total
exposure of 24 ksec. We did not detect any X-ray emission in a circular
50������ extraction region centered on the position of the optical counterpart,
with a 3-sigma threshold of 1.4 x 10-14 erg/cm^2/s in the 3-10 keV band,
assuming an X-ray spectrum with a photon power law index of -2. No source
was detected in the 10-60 keV band, however additional analysis is ongoing
to place limits on possible line emission from nuclear decays. We note that
the NuSTAR hard X-ray band is not sensitive to X-ray emission from star
formation in the host galaxy, and there is no known AGN activity in this
Further NuSTAR observations are planned.