Abstract: Jinghong Xu requests long term photometric monitoring of SN 2026gzf (Type Ic-BL) to search for possible signs of interaction with CSM ejected during a suspected supernova imposter event roughly 8 years earlier. This will place constraints on the nature of the suspected supernova imposter event as well as the heavily stripped supernova progenitor.
Justification: SN 2026gzf is a Type Ic-BL supernova (J2000 coordinate: 09:59:42.889 +00:25:06.40). AT 2018mtl is an unclassified transient (J2000 coordinate: 09:59:42.890 +00:25:06.73). The apparent angular proximity of the two transients (within the positional uncertainty expected of sky surveys like Pan-Starrs1, especially for faint transients) may imply a common progenitor, the former being a SESNe (Stripped Envelope Supernovae) and the latter being an earlier supernova imposter. This is backed by the discovery magnitude of AT 2018mtl: 21.66 (w-P1), which correlates to an absolute magnitude of -14.1, in line with that of a luminous supernova imposter.
If two transients do indeed share a common progenitor, as is the case with SN 2009ip and SN 2015bh, there could be a potential impact between the fast-moving supernova ejecta and the earlier ejecta from the supernova imposter event a few months after the initial core collapse, the exact time depending on their respective expansion velocities.
The impact, especially during its onset, could exhibit the following traits: a sudden deviation relative to the natural development of the original light curve, abnormal color evolution (sudden blue/UV flash) and narrow P-Cygni profiles superimposed on original board P-Cygni lines typical of Ic-BL supernovae.
Johnson U,B,V band and Sloan g,r,i band photometry (especially the Johnson U band) with hourly coverage in the following 6 months are therefore requested, with the goal being to capture the sudden and subtle onset of CSM interaction and to establish a well-sampled light curve. Sloan g, Sloan r and Sloan i band photometry are recommended here to ensure compatibility with ZTF observations which cover the light curve not long after shock breakout. The pre-peak supernova is presently at mag 17.38 (absolute magnitude around -18.4) (g, ZTF, UTC: 2026-3-27, 05:52:30) and is expected to rise further in brightness given the type of the supernova, making it an accessible target.
Such observations could shed light on the mass, the expansion velocity as well as the possible asymmetric distribution of materials within the ejecta shell of the supernova imposter. This, in turn, could put vital constraints of the final stages of a highly stripped star leading up to eventual core collapse.