The Universe hosts a diverse population of astrophysical objects, within our galaxy as well as beyond, that explode, flare up or intensify activity in dramatic and unpredictable fashion across the entire electromagnetic spectrum and over a broad range of timescales spanning milliseconds to years. Collectively designated “transients,” many are known to be prominent emitters of high-energy gamma rays and are also likely sources of non-photonic, multi-messenger signals such as cosmic rays, neutrinos and/or gravitational waves. They are of great scientific interest, being associated with catastrophic events involving relativistic compact objects such as neutron stars and black holes that manifest the most extreme physical conditions in the Universe.
One of CTA’s greatest strengths is its unprecedented sensitivity in VHE gamma rays for transient phenomena and short-timescale variability — far greater compared than satellite-based instruments such as Fermi-LAT. Hence, CTA has potential to break new ground in elucidating the physics of cosmic transients and, with its relatively large field of view, following up alerts of transient events issued by monitoring instruments, as well as discovering transients on its own. The proposed targets comprise six classes of objects: gamma-ray bursts, galactic transients, neutrino alerts, gravitational wave alerts, selected optical/radio transient factory events and serendipitous VHE transients, along with a VHE transient survey.