Occasionally I download and filter a list of recent transients taken from tns-weizmann – to find something interesting to look at.
I imaged 2018bsr last night – perhaps a type IA SN a week to two weeks before maximum (spectrum with Liverpool telescope) – and don’t see any brightening of the galactic host (it is not a significant distance from the centre). I note the discovery mag is low.
Can anyone make sense of all the available information – and put forward a likely identity?
From the sharp H alpha emission line in the spectrum (from the host galaxy) the redshift = ~0.04 which corresponds to ~170MPc distance. The spectrum is clearly a type 1a. At this distance a type 1a SN would reach ~16.9 at maximum, not allowing for any redenning. The ASAS-SN mag 17.2 does seem rather bright for 9-12 days before maximum but ages estimated from the spectra can be notoriously unreliable so it could be closer to maximum than this
The host galaxy brightness from Vizier would be the integrated brightness over the whole galaxy rather than just the core. Perhaps this explains why your measured core brightness is not higher than the Vizier magnitude ? (At a rough estimate, I would expect the SN to have increased the brightness by ~0.5 mag)