Comparison of the physical parameters of the three LRNe in M 31 (adopting μ = 24.47 ± 0.08 mag for M 31): AT 2019zhd, M31-LRN2015 and M31-RV. Top-left: bolometric light curves. Top-right: B − V colour evolution. Bottom-left: evolution of the blackbody temperature evolution. Bottom-right: evolution of the radius. The data of M31-RV are from Boschi & Munari (2004), those of M31-LRN2015 are from Kurtenkov et al. (2015), Williams et al. (2015), Lipunov et al. (2017), Blagorodnova et al. (2020). For the total reddening of the comparison objects, we adopt E(B − V) = 0.37 mag for M31-LRN2015 (from Kurtenkov et al. 2015), and E(B − V) = 0.12 mag for M31-RV (Boschi & Munari 2004).