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A Progenitor Candidate for SN 2017ein in NGC 3938

ATel #10485; Schuyler D. Van Dyk (Caltech/IPAC), Alexei V. Filippenko (UC Berkeley), Ori D. Fox (STScI), Patrick L. Kelly (UC Berkeley), Dan Milisavljevic (Harvard/CfA), and Nathan Smith (Univ. Arizona)
on 13 Jun 2017; 04:51 UT
Credential Certification: Schuyler D. Van Dyk (vandyk@ipac.caltech.edu)

Subjects: Optical, Supernovae, Transient

We report the identification of a progenitor candidate for the Type Ic SN 2017ein in NGC 3938 (ATel #10434, #10481) in archival Hubble Space Telescope (HST) images obtained with the Wide Field Planetary Camera 2 (WFPC2) on 2007 December 11 UT in bands F555W and F814W, as part of program GO-10877 (PI: A.V. Filippenko). We have isolated the candidate in the archival data via imaging of the SN obtained on 2017 June 12 UT with the HST Wide Field Camera 3 (WFC3) UVIS channel in F438W, as part of our Target-of-Opportunity program GO-14645 (PI: S.D. Van Dyk). Using 27 point-like objects in common between the two image datasets, with a formal astrometric root-mean-square uncertainty of 0.26 WFPC2/WF pixel, we find that the SN position and the centroid of the identified point-like object in the WFPC2 images are consistent to within 0.36 pixel. We measured photometry for the candidate from the WFPC2 data using Dolphot (Dolphin 2000, PASP, 112, 1397) and found F555W = 24.81 +/- 0.11 and F814W = 24.88 +/- 0.19 Vegamag. Assuming a distance modulus 31.17 +/- 0.10 mag from the Extragalactic Distance Database and only Galactic foreground extinction toward the SN position from Schlafly & Finkbeiner (2011, ApJ, 737, 103; via the NASA/IPAC Extragalactic Database), and also assuming F555W ~ V and F814W ~ I, this would imply that M_V ~ -6.4 and M_I ~ -6.3 mag for the object. The progenitor candidate therefore would be intrinsically relatively blue and luminous, and could be even bluer and more luminous with additional reddening internal to the host galaxy. Further observations of the SN and analysis of the progenitor candidate are underway.