The very nearby Type Ia supernova 2014J in M82 offers a rare opportunity to study the physics of thermonuclear supernovae at extremely late phases ( \gtrsim 800 days ) .
Using the Hubble Space Telescope , we obtained six epochs of high precision photometry for SN 2014J from 277 days to 1181 days past the B - band maximum light .
The reprocessing of electrons and X-rays emitted by the radioactive decay chain ^ { 57 } Co \rightarrow ^ { 57 } Fe are needed to explain the significant flattening of both the F 606 W -band and the pseudo-bolometric light curves .
The flattening confirms previous predictions that the late-time evolution of type Ia supernova luminosities requires additional energy input from the decay of ^ { 57 } Co ( 56 ) .
By assuming the F 606 W -band luminosity scales with the bolometric luminosity at \sim 500 days after the B - band maximum light , a mass ratio ^ { 57 } Ni/ ^ { 56 } Ni \sim 0.065 _ { -0.004 } ^ { +0.005 } is required .
This mass ratio is roughly \sim 3 times the solar ratio and favors a progenitor white dwarf with a mass near the Chandrasekhar limit .
A similar fit using the constructed pseudo-bolometric luminosity gives a mass ratio ^ { 57 } Ni/ ^ { 56 } Ni \sim 0.066 _ { -0.008 } ^ { +0.009 } .
Astrometric tests based on the multi-epoch HST ACS/WFC images reveal no significant circumstellar light echoes in between 0.3 pc and 100 pc ( 71 ) from the supernova .