Top panel: radial density profile in IRAS 15398 (black), along with the temperatures in the quiescent phase (blue) and during the burst (red). Other panels: radial abundance profiles of CO, H₂O, N₂H⁺, and HCO⁺. The red curves are during the accretion burst. The black curves are during the quiescent phase, at increasing amounts of time after the burst: 10 yr (dotted), 150 yr (solid), 800 yr (dotted), 2600 yr (short-dashed), 6200 yr (dash-dotted), and 24 000 yr (long-dashed). The quiescent profiles culminate in the blue curve at 1 × 10⁵ yr after the burst.