Luminosity-duration relations and luminosity functions of repeating and
  non-repeating fast radio bursts
  Fast radio bursts (FRBs) are mysterious radio bursts with a time scale of
approximately milliseconds. Two populations of FRB, namely repeating and
non-repeating FRBs, are observationally identified. However, the differences
between these two and their origins are still cloaked in mystery. Here we show
the time-integrated luminosity-duration ($L_{\nu}$-$w_{\rm int,rest}$)
relations and luminosity functions (LFs) of repeating and non-repeating FRBs in
the FRB Catalogue project. These two populations are obviously separated in the
$L_{\nu}$-$w_{\rm int,rest}$ plane with distinct LFs, i.e., repeating FRBs have
relatively fainter $L_{\nu}$ and longer $w_{\rm int,rest}$ with a much lower
LF. In contrast with non-repeating FRBs, repeating FRBs do not show any clear
correlation between $L_{\nu}$ and $w_{\rm int,rest}$. These results suggest
essentially different physical origins of the two. The faint ends of the LFs of
repeating and non-repeating FRBs are higher than volumetric occurrence rates of
neutron-star mergers and accretion-induced collapse (AIC) of white dwarfs, and
are consistent with those of soft gamma-ray repeaters (SGRs), type Ia
supernovae, magnetars, and white-dwarf mergers. This indicates two
possibilities: either (i) faint non-repeating FRBs originate in neutron-star
mergers or AIC and are actually repeating during the lifetime of the
progenitor, or (ii) faint non-repeating FRBs originate in any of SGRs, type Ia
supernovae, magnetars, and white-dwarf mergers. The bright ends of LFs of
repeating and non-repeating FRBs are lower than any candidates of progenitors,
suggesting that bright FRBs are produced from a very small fraction of the
progenitors regardless of the repetition. Otherwise, they might originate in
unknown progenitors.
