Thermal evolution of the FP model with and without Joule heating. Curve 1: Be = 1.5 × 1013 G, ρ0 = 1014 g cm−3, ξ = 0.1. Curve 2: Be = 1.5 × 1013 G, ρ0 = 1013 g cm−3, ξ = 0.1. Curve 3: Be = 1.5 × 1013 G, ρ0 = 1014 g cm−3, ξ = 0.01. Curve 4: Be = 5 × 1012 G, ρ0 = 1014 g cm−3, ξ = 0.1. Curve 5: without Joule heating.