The fading of supernova 1997D

We present a new set of spectroscopic and photometric data extending the observations of SN 1997D to over 400d after the explosion. These observations confirm the peculiar properties of SN 1997D, such as the very low abundance of ⁵⁶Co (0.002M⊙) and the low expansion velocity of the ejecta (∼1000 km s^-1). We discuss the implications of these observations for the character of the progenitor and the nature of the remnant, showing that a Crab-like pulsar or an accreting neutron star formed in the explosion of a low-mass progenitor should already have produced a detectable luminosity at this epoch, in contrast with photometric data. On the other hand, the explosion of a high-mass progenitor with the formation of a black hole is consistent with the available observations. The consequences of this conclusion regarding the nature of the explosion and the prospects of directly identifying the black hole are also addressed.