  This work presents the observations and analysis of ATLAS19dqr/SN 2019bkc, an
extraordinary rapidly evolving transient event located in an isolated
environment, tens of kiloparsecs from any likely host. Its light curves rise to
maximum light in $5-6$ d and then display a decline of $\Delta m_{15} \sim5$
mag. With such a pronounced decay, it has one of the most rapidly evolving
light curves known for a stellar explosion. The early spectra show similarities
to normal and `ultra-stripped' type Ic SNe, but the early nebular phase
spectra, which were reached just over two weeks after explosion, display
prominent calcium lines, marking SN 2019bkc as a Ca-rich transient. The Ca
emission lines at this phase show an unprecedented and unexplained blueshift of
10,000 -- 12,000 km/s. Modelling of the light curve and the early spectra
suggests that the transient had a low ejecta mass of $0.2 - 0.4$ M$_\odot$ and
a low kinetic energy of $ (2-4)\times 10^{50}$ erg, giving a specific kinetic
energy $\sim1$ [$10^{51}$ erg]/M$_\odot$. The origin of this event cannot be
unambiguously defined. While the abundance distribution used to model the
spectra marginally favours a progenitor of white dwarf origin through the
tentative identification of \ArII, the specific kinetic energy, which is
defined by the explosion mechanism, is found to be more similar to an
ultra-stripped core-collapse events. SN 2019bkc adds to the diverse range of
physical properties shown by Ca-rich events.
