Restrictions for the position of NGC 300 ULX1 in the ṁ₀ − μ plane. The red horizontal line corresponds to the luminosity of 4.7 × 10³⁹ erg s⁻¹ assuming accretion efficiency η ≃ 0.15. The black solid line corresponds to p_eq = p = 20 s. The dotted spin-up line shows the lower limit for ṁ₀ set by inequality (32) using period derivation |ṗ| = 5.5 × 10⁻⁷ s s⁻¹ (Carpano et al. 2018). We use here M = 1.4 M_⊙, R = 10 km, I = 1.5 × 10⁴⁵ g cm², and p = 20 s.