AstroNote 2023-119

Following the report of a new candidate supernova in M101 by K. Itagaki, we acquired observations on the 2m Liverpool Telescope using the IO:O CCD imager and the SPRAT low-resolution spectrograph.  The imaging observations confirm that the source is still present, with a refined position of RA=14:03:38.51, dec=54:18:42:10.  Preliminary photometry gives approximate magnitudes of g=13.94, r=14.16 at this time (MJD 60083.92314).

The spectrum shows a blue continuum with numerous strong emission lines superimposed.  The line profiles are described by a narrow core with a intermediate-width Thomson-scattered base, similar to what has been seen in early spectra of Type II SNe at very early phases following shock breakout (e.g., Yaron et al. 2017, Nature Physics 13, 510).   Identified species include H, He II, He I, N III, N IV, C III, and C IV.  At a distance of only ~6.4 Mpc, this would represent among the closest core-collapse supernovae found in the past several decades, comparable to SN 2011dh (~8.4 Mpc) and SN 2017eaw (~7.7 Mpc).

We have requested further LT follow-up as well as observations with Swift and HST.  Additional follow-up is encouraged.