Early Blue Excess from the Type Ia Supernova 2017cbv and Implications for Its Progenitor

Griffin Hosseinzadeh, David J. Sand, Stefano Valenti, Peter Brown, D. Andrew Howell, Curtis McCully, Daniel Kasen, Iair Arcavi, K. Azalee Bostroem, Leonardo Tartaglia, Eric Y. Hsiao, Scott Davis, Melissa Shahbandeh, Maximilian D. Stritzinger

Research output: Contribution to journalArticlepeer-review

122 Scopus citations


We present very early, high-cadence photometric observations of the nearby Type Ia SN 2017cbv. The light curve is unique in that it has a blue bump during the first five days of observations in the U, B, and g bands, which is clearly resolved given our photometric cadence of 5.7 hr during that time span. We model the light curve as the combination of early shocking of the supernova ejecta against a nondegenerate companion star plus a standard SN Ia component. Our best-fit model suggests the presence of a subgiant star 56 R from the exploding white dwarf, although this number is highly model-dependent. While this model matches the optical light curve well, it overpredicts the observed flux in the ultraviolet bands. This may indicate that the shock is not a blackbody, perhaps because of line blanketing in the UV. Alternatively, it could point to another physical explanation for the optical blue bump, such as interaction with circumstellar material or an unusual nickel distribution. Early optical spectra of SN 2017cbv show strong carbon (C ii λ6580) absorption up through day -13 with respect to maximum light, suggesting that the progenitor system contains a significant amount of unburned material. These early results on SN 2017cbv illustrate the power of early discovery and intense follow-up of nearby supernovae to resolve standing questions about the progenitor systems and explosion mechanisms of SNe Ia.

Original languageEnglish (US)
Article numberL11
JournalAstrophysical Journal Letters
Issue number2
StatePublished - Aug 20 2017


  • supernovae: general
  • supernovae: individual (SN 2017cbv)

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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