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

Abstract

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 $r^{\prime }$ and $i^{\prime }$ 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${}_{\odot }$ during each eruption, and an enhanced Helium abundance of He/He${}_{\odot }$ $\approx$ 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 ${\mathrm{M}}_{\mathrm{WD}}$$-\dot{M}$ plane yields the mass of a CO WD, powering the ``H-shell flashes'' every $\sim$ 1 year to be $>1.36$ M${}_{\odot }$ and growing with time, making M31N 2008-12a a strong candidate for the single degenerate scenario of Type Ia supernovae progenitor.

Accepted for publication in ApJ, 23 pages, 12 figures, 5 tables