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Detection of a Blue Point Source at the Location of Supernova 2011dh

ATel #6375; Gaston Folatelli (Kavli IPMU), Schuyler D. Van Dyk (IPAC/Caltech), Omar G. Benvenuto (IALP/UNLP), Melina C. Bersten (Kavli IPMU), Hanindyo Kuncarayakti (MAS/University of Chile), Keiichi Maeda (Kyoto University), Ken'ichi Nomoto (Kavli IPMU), Robert M. Quimby (SDSU)
on 7 Aug 2014; 19:28 UT
Credential Certification: Gaston Folatelli (gaston.folatelli@ipmu.jp)

Subjects: Optical, Ultra-Violet, Binary, Supernovae

We report Hubble Space Telescope (HST) observations of the field of the Type IIb Supernova 2011dh in M51 performed with the Wide Field Camera 3 (WFC3), UVIS channel and filters F225W and F336W on 2014 August 7.2 UT as part of our Cycle 21 program GO-13426 (PI: G. Folatelli; joined with GO-13433, PI: J. Maund). The near-UV images show the presence of a blue point source at the location of the SN. We are confident that the new object is coincident with the fading SN that Van Dyk et al. (2013, ApJ, 772, L32) identified in WFC3 images from 2013 to 0.07 UVIS pixel, or 2.8 milliarcsec (i.e., 0.1 pc at the assumed distance of 8.4 Mpc for M51). Preliminary photometry done with the Dolphot v2.0 (Dolphin 2000, PASP, 112, 1383) package yielded flight-system magnitudes of F225W = 24.6 +/- 0.1 mag, and F336W = 24.9 +/- 0.1 mag. The source's UV brightness and color is compatible with it being the companion star of the disappeared yellow supergiant progenitor (Van Dyk et al. 2013, ApJL, 772, L32; Ergon et al. 2014, A&A, 562, 17). We estimate the flux from the SN ejecta to be negligible in this wavelength range. If the contribution from an unresolved light echo can be discarded, this detection provides further confirmation for the interacting binary progenitor proposed by Bersten et al. 2012, ApJ, 757, 31, and Benvenuto, Bersten, & Nomoto 2013, ApJ, 762, 74. More detailed analysis is ongoing.