X-ray detection of SN 2016gkg with Swift-XRT

ATel #9561; R. Margutti (Northwestern Univ.), M. R. Drout (Carnegie Observatories), P. J. Brown (Texas A&M/Mitchell Institute), S. Dong (KIAA-PKU), D. Milisavljevic (SAO), A. Zauderer (NYU), A. Kamble (Harvard Univ.)
on 28 Sep 2016; 19:31 UT
Credential Certification: Raffaella Margutti (rmargutti@cfa.harvard.edu)

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Swift-XRT started observing SN 2016gkg (Atel #9521, #9526, #9528, #9529, #9536, #9556) on Sep 21, 2016 until Sep 27, 2016 for a total exposure time of 15.2 ks (PIs Dong, Drout, Brown). An X-ray source is detected at the position of the transient with significance of 5.5 sigma in the 0.3-10 keV range, and count-rate (4.1 +/- 0.7)d-3 c/s. Assuming a power-law spectral model with Galactic absorption 1.65d20 1/cm2 (Kalberla 2005) we infer a best-fitting power-law index Gamma=0.8 +\- 0.4 With these spectral parameters we derive an average unabsorbed flux of ~3.1d-13 erg/s/cm2 (0.3-10 keV), corresponding to a luminosity ~2.2d40 erg/s at the distance of 26.4 Mpc (Nasonova, de Freitas Pacheco, & Karachentsev, 2011). Our analysis shows that the X-ray source faded significantly during the six days of monitoring. We therefore conclude that the X-ray source is physically associated with SN2016gkg. We thank the Swift team for scheduling these ToO observations.