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Possible Identification of the Progenitor of SN 2016adj in NGC 5128 (Centaurus A)

ATel #8693; Schuyler D. Van Dyk (IPAC/Caltech), Joana Ascenso (U. Porto), Ya-Lin Wu, Nathan Smith, Laird M. Close, Jared R. Males, Katie Morzinski (U. Arizona), Ryan J. Foley (U. Illinois), Saurabh Jha (Rutgers U.), Adam A. Miller (JPL/Hubble Fellow), Alexei V. Filippenko (UC Berkeley), Joao Alves (U. Vienna)
on 14 Feb 2016; 18:52 UT
Credential Certification: Schuyler D. Van Dyk (vandyk@ipac.caltech.edu)

Subjects: Infra-Red, Optical, Supernovae

Referred to by ATel #: 8720, 8759

We report the identification of the progenitor star of the Type IIb SN 2016adj (ATel #8651, #8663, #8664) in archival Hubble Space Telescope (HST) WFC3/UVIS image data obtained in 2010 July and near-infrared JHKs images obtained in 2008 July with the NAOS+CONICA (NACO) instrument on the ESO VLT UT4-Yepun (PI: J. Alves; see Kainulainen et al. 2009, A&A, 502, L5). We acquired a coadded image of the SN on 2016 February 13 UT in z'-band with the Magellan 6.5-m Clay AO system (MagAO) VisAO camera and registered it (without distortion correction) to the WFC3 image mosaic in F814W (~I-band), using 14 stars in common, to ~0.19 UVIS pixel or ~8 mas. A star with brightness at F814W of 23.1 mag is near to this position (at ~5 sigma) in the HST image. We tentatively assign this star as the candidate progenitor, which also has apparent counterparts in the JHKs images. The star does not appear to be detected in any WFC3 data shortward of F814W. From its brightness in this band alone, adjusting to an assumed reddening to the SN (and to the progenitor) of E(B-V)~1 mag (ATel #8657) and a distance modulus of 27.67 mag (Ferrarese et al. 2007, ApJ, 654, 186), we find that the star would be less luminous (at M_I ~ -6.4 mag) than the progenitors of the SNe IIb 1993J (e.g, Aldering et al. 1994, AJ, 107, 662) and 2013df (Van Dyk et al. 2014, AJ, 147, 37) and more consistent with the luminosity of the progenitor of SN 2008ax (Folatelli et al. 2015, ApJ, 811, 147), implying that SN 2016adj may be a 'compact', rather than 'extended', SN IIb (Chevalier & Soderberg 2010, ApJ, 711, L40). We also measure preliminary JHKs photometry for the star of 24.5, 24.5, and 24.2 mag (with a ~1 mag uncertainty in Ks), respectively, which is odd, given the I-band brightness, but could imply that the star was varying significantly in the years before explosion (e.g., Szczygiel et al. 2012, ApJ, 747, 23). Further analysis is ongoing.