Multi-wavelength observations of multiple eruptions of the recurrent nova M31N 2008-12a

We report the optical, UV, and soft X-ray observations of the 2017-2022 eruptions of the recurrent nova M31N 2008-12a. We infer a steady decrease in the accretion rate over the years based on the inter-eruption recurrence period. We find a “cusp” feature in the r' and i' band light curves close to the peak, which could be associated to jets. Spectral modelling indicates a mass ejection of 10^-7 to 10^-8 M_⊙ during each eruption, and an enhanced Helium abundance of He/He_⊙ ≈ 3. The super-soft source (SSS) phase shows significant variability, which is anti-correlated to the UV emission, indicating a common origin. The variability could be due to the reformation of the accretion disk. A comparison of the accretion rate with different models on the M_WD-Ṁ plane yields the mass of a CO WD, powering the “H-shell flashes” every ∼ 1 year to be >1.36 M_⊙ and growing with time, making M31N 2008-12a a strong candidate for the single degenerate scenario of Type Ia supernovae progenitor.