Celestial fireworks: revealing the physics of the time-variable sky

Periodic Reporting for period 3 - Fireworks (Celestial fireworks: revealing the physics of the time-variable sky)

Reporting period: 2020-09-01 to 2022-02-28

Summary of the context and overall objectives of the project

This project is aimed at studying transient astrophysical phenomena on timescales shorter than previously possible - nightly (subproject 1), hourly (subproject 2) and down to minure/second timescale (subproject 5), as well as to collect and analyse large samples of such events (subproject 3) and to develop new tools and methods that will help to find unusual objects (subproject 4).

Understanding transient astrophysical phenomena is a key to understanding fundamental problems in astrophysics and physics in general, and move our understanding of the physical universe surrounding us forward.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

All subprojects are progressing, with numerous results having been published from subprojects 1-4; subproject 5 has achieved a critical milestone in deployment of the W-FAST telescope, and the first paper is in preparation.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

We have:

* measured for the first time the fraction of all massive stars that explode within clouds of surrounding matter, and showed this is ubiquitous (60% of cases), indicating that massive stars undergo a period of rapid
mass loss prior to their terminal explosion; this is unexplained by standard models of stellar evolution, and require a new thinking about massive star evolution, structure, and explosion as supernovae.

* We have found the first example of an exploding star within a Wolf-Rayet wind nebula.

* We have contributed to the discovery of the first gravitational-wave counterpart, GW170817.