Discovering novae in early-type galaxies with MUSE: A chance find in NGC
  1404, and twelve more candidates from an archival search
  I report the discovery of a transient broad-H$\alpha$ point source in the
outskirts of the giant elliptical galaxy NGC 1404, discovered in archival
observations taken with the MUSE integral field spectrograph. The H$\alpha$
line width of 1950 km s$^{-1}$ FWHM, and luminosity of
(4.1$\pm$0.1)$\times$10$^{36}$ erg s$^{-1}$, are consistent with a nova
outburst, and the source is not visible in MUSE data obtained nine months
later. A transient soft X-ray source was detected at the same position (within
$<$1 arcsec), 14 years before the H$\alpha$ transient. If the X-ray and
H$\alpha$ emission are from the same object, the source may be a
short-timescale recurrent nova with a massive white dwarf accretor, and hence a
possible Type-Ia supernova progenitor. Selecting broad-H$\alpha$ point sources
in MUSE archival observations for a set of nearby early-type galaxies, I
discovered twelve more nova candidates with similar properties to the NGC 1404
source, including five in NGC 1380 and four in NGC 4365. Multi-epoch data are
available for four of these twelve sources; all four are confirmed to be
transient on $\sim$1 year timescales, supporting their identification as novae.
