The main progenitor candidate of Type Ia supernovae ( SN Ia ) is white dwarfs in binary systems where the companion star is another white dwarf ( double degenerate system ) or a less evolved non-degenerate star with R _ { * } \gtrsim 0.1 ~ { } R _ { \odot } ( single degenerate system ) , but no direct observational evidence exists that tells which progenitor system is more common .
Recent studies suggest that the light curve of a supernova shortly after its explosion can be used to set a limit on the progenitor size , R _ { * } .
Here , we report a high cadence monitoring observation of SN 2015F , a normal SN Ia , in the galaxy NGC 2442 starting about 84 days before the first light time .
With our daily cadence data , we catch the emergence of the radioactively powered light curve , but more importantly detect with a > 97.4 % confidence a possible dim precursor emission that appears at roughly 1.5 days before the rise of the radioactively powered emission .
The signal is consistent with theoretical expectations for a progenitor system involving a companion star with R _ { * } \simeq 0.1 – 1 ~ { } R _ { \odot } or a prompt explosion of a double degenerate system , but inconsistent with a typically invoked size of white dwarf progenitor of R _ { * } \sim 0.01 ~ { } R _ { \odot } .
Upper limits on the precursor emission also constrain the progenitor size to be R _ { * } \lesssim 0.1 ~ { } R _ { \odot } , and a companion star size of R _ { * } \lesssim 1.0 ~ { } R _ { \odot } , excluding a very large companion star in the progenitor system .
Additionally , we find that the distance to SN 2015F is 23.9 \pm 0.4 Mpc .