Multi-wavelength light curve model of the one year recurrence period nova M31N 2008-12a

Abstract

We present a theoretical light curve model of the recurrent nova M31N 2008-12a, the current record holder for the shortest recurrence period (1 year).We combined interior structures calculated using a Henyey-type evolution code with optically thick wind solutions of hydrogen-rich envelopes, which give the proper mass-loss rates, photospheric temperatures, and luminosities. The light curve model is calculated for a 1.38 M⊙ white dwarf (WD) with an accretion rate of 1.6 × 10-7 M⊙ yr-1. This model shows a very high effective temperature (log Tph (K) > 4.97) and a very small wind mass-loss rate (Mwind < 9.3 × 10-6 M⊙ yr-1) even at the maximum expansion of the photosphere. These properties are consistent with the faint optical peak of M31N 2008-12a because the brightness of the free-free emission is proportional to the square of the mass-loss rate. The model well reproduces the short supersoft X-ray turn-on time of 6 days and turn-off time of 18 days after the outburst. The ejecta mass of our model is calculated to be 6.3 × 10 M⊙ 8 , corresponding to 37% of the accreted mass. The growth rate of the WD is 0.63 times the mass accretion rate, making it a progenitor for a SN Ia. Our light curve model predicts a bright supersoft X-ray phase one or two days before the optical peak. We encourage detection of this X-ray flash in future outbursts.