Probing Relativistic Axions from Transient Astrophysical Sources
  Emission of relativistic axions from transient sources, such as axion star
explosions, can lead to observable signatures. We show that axion bursts from
collapsing axion stars can be detectable over the wide range of axion masses
$10^{-15} \, \textrm{eV} \lesssim m \lesssim 10^{-7} \, \textrm{eV}$ in
laboratory experiments, such as ABRACADABRA, DMRadio and SHAFT. The detection
of axion bursts could provide new insights into the fundamental axion
potential, which is challenging to probe otherwise. An ensemble of bursts in
the distant past would give rise to a diffuse axion background distinct from
the usual cold axion DM. Coincidence with other signatures would provide a new
window into multi-messenger astronomy.
