Astron. Astrophys. 344, 459-471 (1999)

6. Estimating a SN Ia rate inferred from the population of supersoft sources in M31

Assuming a total number of 1000-10,000 active supersoft sources in M31 as follows from an analysis in paragraph 4.3 and applying the cumulative mass distribution from Fig. 3 gives a fraction of 26% in the and 32% in the hydrogen-burning shell approximation for white dwarf masses in excess of . Assuming that all objects with white dwarf masses in excess of explode as type Ia supernovae after a typical life time of years, a SN Ia rate of is inferred (in both approximations). Assuming that all objects with white dwarf masses in excess of explode as type Ia supernovae after a typical life time of years (cf. Yungelson et al. 1995), a SN Ia rate of is inferred (for the two approximations). Supersoft sources could then contribute up to a rate of . Capellaro et al. (1997) assuming our Galaxy to be a spiral of type Sb or Sc, detected a Type Ia supernova rate of which for M31, with is about two times larger mass, means: . It thus seems that the supersoft X-ray sources can make a major contribution to the Type Ia SN rate in M31.

In is interesting to note that the historical supernova SN 1885 (S And) might be a subluminous SN Ia (Chevalier & Plait 1988, Fesen et al. 1998). This supernova is located in the bulge of M31.

© European Southern Observatory (ESO) 1999

Online publication: March 18, 1999
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