A Light Curve Analysis of Recurrent and Very Fast Novae in our Galaxy, Magellanic Clouds, and M31

We analyzed optical, UV, and X-ray light curves of 14 recurrent and very fast novae in our galaxy, Magellanic Clouds, and M31, and obtained their distances and white dwarf (WD) masses. Among the 14 novae, we found that eight novae host very massive ($\gtrsim 1.35 M_\odot$) WDs and are candidates of Type Ia supernova (SN Ia) progenitors. We confirmed that the same timescaling law and time-stretching method as in galactic novae can be applied to extra-galactic fast novae. We classify the four novae, V745 Sco, T CrB, V838 Her, and V1534 Sco, as the V745 Sco type (rapid-decline), the two novae, RS Oph and V407 Cyg, as the RS Oph type (circumstellar matter(CSM)-shock), and the two novae, U Sco and CI Aql, as the U Sco type (normal-decline). The $V$ light curves of these novae almost overlap with each other in the same group, if we properly stretch in the time direction (timescaling law). We apply our classification method to LMC, SMC, and M31 novae. YY Dor, LMC N 2009a, and SMC N 2016 belong to the normal-decline type, LMC N 2013 to the CSM-shock type, and LMC N 2012a and M31N 2008-12a to the rapid-decline type. We obtained the distance of SMC N 2016 to be $d=20\pm2$ kpc, suggesting that SMC N 2016 is a member of our galaxy. The rapid-decline type novae have very massive WDs of $M_{\rm WD}=1.37-1.385 M_\odot$ and are promising candidates of SN Ia progenitors. This type of novae are much fainter than the MMRD relations.