Irradiation-driven Formation of Supersoft X-Ray Sources following Classical Novae

Abstract Supersoft X-ray sources (SSSs) are characterized by persistent thermonuclear burning on the surfaces of white dwarfs (WDs). The standard model requires high mass-transfer rates of ∼10 −7 M ⊙ yr −1 from massive companions, presenting a theoretical impediment to the observed short-period SSSs, whose orbital periods imply low-mass donors theoretically incapable of sustaining such accretion. To resolve this paradox, we propose and demonstrate through detailed simulations that irradiative feedback following a classical nova eruption provides a natural formation channel. Through detailed binary evolution simulations with MESA, we reveal that sustained WD irradiation—initially from the outburst and subsequently from accretion luminosity—triggers significant and stable expansion of the low-mass companion. This, in turn, drives mass-transfer rates into the stable hydrogen-burning regime and sustains it beyond 10 4 yr after the initiation of hydrogen burning. This mechanism robustly explains the observed population of short-period SSSs. Moreover, when the irradiation-driven mass-transfer rate drops below the stable accretion rate, it may lead to the rapid accumulation of sufficient material on shorter timescales to trigger a recurrent nova outburst instead of SSS, thereby also offering an explanation for the origin of short-period recurrent novae.