Top: Comparison of CSM and magnetar (magnetization ε_B = 10⁻⁶) spectral models of SN 2017egm at a distance of 135 Mpc together with Fermi-LAT (this work) and VERITAS (Acharyya et al. 2023) observations. In the CSM model, the predicted flux is shown with or without γ − γ absorption (see Appendix C), highlighting the fact that no emission is expected above 50 GeV. A simulation of 50 hours of CTAO-North observations between 50 GeV and 10 TeV is also shown for the magnetar model (see Sect. 7 for more details). For clarity only detection flux points (where TS > 4) are shown and upper limits are omitted. Using the CTAO simulation shown above, below we display the significance of a SN 2017egm-like source at different distances in the magnetar model only.