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Pre-explosion upper limit for SN 2016adj from archival Chandra data

ATel #8677; T. Heikkila, S. Tsygankov, S. Mattila (Turku), M. Fraser (IoA)
on 11 Feb 2016; 13:34 UT
Credential Certification: Seppo Mattila (seppo.mattila@utu.fi)

Subjects: X-ray, Supernovae

Following Heikkila et al. (2016, MNRAS 457, 1107), we considered the possibility of finding a HMXB progenitor to SN 2016adj (ATel #8651) classified as a likely Type II SN (ATels #8655, #8664). We combined all publicly available pre-explosion ACIS observations from Chandra (total combined exposure time 958.7 ks). No X-ray source was found near the reported SN position, the closest source being the unclassified X-ray source CXOU J132523.9-430059 at the radial distance of 2.5". Adopting a distance of 3.66 Mpc (Tully et al, 2013, AJ 146, 86) and assuming absorbed power law model with photon index 0.5 and hydrogen column density Nh=2*10^22 cm^-2 (given the SN is highly reddened; ATels #8654, #8655, #8657, #8662, #8664, #8665), we measured an unabsorbed 3sigma X-ray luminosity upper limit of 2.8*10^36 erg/s using the method described in Heikkila et al. (2016). This limit is comparable to that obtained for the Type IIb SN 2011dh. While it is currently unclear what the precise subtype of SN 2016adj is, if it is a Type IIb SN then the limit is among the most restrictive for a stripped envelope SN. We also measured the X-ray luminosity of CXOU J132523.9-430059 for each available ACIS observation separately, using the same model and assuming the same distance we note that it is variable between 2.0*10^37 and 8.5*10^37 erg/s.