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Type-Ia SN 2016coj - limits on progenitors from pre-explosion HST images

ATel #9207; Matan Friedmann, Dan Maoz (Tel-Aviv University)
on 4 Jul 2016; 13:32 UT
Credential Certification: Dan Maoz (Tel-Aviv University) (maoz@astro.tau.ac.il)

Subjects: Optical, Supernovae

We have analyzed archival Hubble Space Telescope WFPC2 images of the site of the Type-Ia SN2016coj (ATEL#9095, #9193) in NGC 4125 in five filters taken on several pre-explosion epochs: F336W from 2009 (~U band, 6600 s total), F439W from 2009 (~B band, 2100 s total), F555W from 1999 (~V band, 1400 s total), F702W from 1997 (~R band, 1000 s total) and F814W (~I band, 2000 s total). Using bright stars near NGC 4125, we have aligned the HST images to an image of the supernova obtained on 2016, June 1 with the Wise Observatory Jay Baum Rich 0.7m telescope in 3 arcsec seeing. We detect no point sources to within 3 arcsec of the explosion site in the archival HST images. By planting fake point sources at the location of the SN, we obtain 3-sigma flux upper limits (AB magnitudes) 26.8 (F336W), 25.8 (F439W), 24.8 (F555W), 24.6 (F702W) and 24.7 (F814W). The Milky Way extinction values in the direction of NGC 4125 are A_U=0.08 mag, A_B=0.07 mag, A_V=0.05 mag, A_R=0.04 mag and A_I=0.03 mag (Schlafly & Finkbeiner 2011), and the distance modulus of the galaxy is 31.89+/-0.25 (Tonry et al. 2001, ApJ, 546, 681). The progenitor of SN2016coj was therefore fainter than absolute magnitudes M_U~-5.1, M_B~-6.2, M_V~-7.1, M_R~-7.3 and M_I~-7.3.