Allowed range for the neutron star mass and radius obtained from the QPOs observed in GRB 200415A and shown in Fig. 6 compared to the mass and radius range derived via the empirical formula given in Sotani et al. (2014), (bottom right region). For defining the low-mass models, we used η = 70.6 − 118.5 MeV (shaded region) and η_QPO = 90.5 − 111.5 MeV (the region enclosed by the solid lines). Here we make the assumption that ρ_c ≤ 2ρ₀. The black and blue dashed lines denote the neutron star radii expected from the empirical relation for η = 70.6, 90.5, 111.5, and 118.5 MeV with ρ_c = 2ρ₀.