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tokens: for non-degenerate companion stars to SNe Ia (Ruiz-Lapuente et al. 2018 ). Woods et al. ( 2017 , 2018 ) have searched for the extended, ionized nebulae around Galactic and LMC SN remnants that are expected for an SSS progenitor to SNe Ia, and similar to analysis of pre-explosion X-ray imaging, they rule out the most luminous and hottest of these sources. Also similar to our analysis of NGC 4696, analysis by Gilfanov Bogdán ( 2010 ) and Johansson et al. ( 2016 ) do not find a large population of SSS in elliptical galaxies that could produce SNe Ia at their observed rates, suggesting that the SSS phase is either very short-lived, occurs at low X-ray luminosities, is significantly obscured by circumstellar material, or does not precede a large fraction of SNe Ia in elliptical galaxies. Combined with the growing sample of optical and X-ray limits in the literature (Maoz Mannucci 2008 ; Nelemans et al. 2008 ; Li et al. 2011 ; Nielsen et al. 2013 , 2014 ; Kelly et al. 2014 ), our SN 2017ejb limits rule out interesting regions in WD temperature and luminosity for plausible progenitor systems. In particular, we can rule out most systems near the Chandrasekhar limit, assuming they were stably accreting for years before explosion. Combined with the limits from SNe 2011fe, 2012fr, and 2014J, we conclude at the 95 per cent confidence level that 47 per cent of SNe Ia explode from systems involving a stably accreting Chandrasekhar-mass SSS. With the growing body of evidence against typical SSS phases in particular and many single-degenerate scenarios in general as the progenitors of SNe Ia, theoretical and observational focus must shift towards the evolutionary pathways and detectable signatures of binary WD systems as the progenitors of SNe Ia (such high-velocity WD runaways from the dynamically driven double-degenerate double-detonation scenario; Shen et al. 2018 ). Future analysis of pre-explosion imaging for all SNe Ia can be used to verify or constrain expectations for the configuration of their progenitor systems and explosion scenarios. In light of the wide variety of SN Ia explosion models, this type of analysis provides one of the most promising lines of inquiry for resolving the SN Ia progenitor problem. 6 CONCLUSIONS We analyse post-explosion imaging and spectroscopy of SN 2017ejb and pre-explosion HST and Chandra imaging of its explosion site. In summary, we find: SN 2017ejb is a low-luminosity SN Ia with strong C ii absorption features in its pre-maximum spectra. Photometrically, it has a low peak luminosity, it declines quickly, and it lacks a secondary i -band maximum. Spectroscopically, it is similar to SN 1986G, but with relatively weak Ti ii bands. Overall, it is most similar to low-luminosity SNe Ia such as SNe 1986G and 1991bg. We do not detect any counterpart to SN 2017ejb in pre-explosion Chandra imaging. Assuming that any pre-explosion Chandra source resembles a blackbody obscured by Milky Way extinction, our limits correspond to at