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4 pi sky: Extreme Astrophysics with Revolutionary Radio Telescopes

Final Report Summary - 4PI-SKY (4 pi sky: Extreme Astrophysics with Revolutionary Radio Telescopes)

The ERC-funded 4 PI SKY project created over a period a six years a research team based at The University of Oxford whose goal was to observe and understand the most extreme astrophysical events since the big bang. The programme had a focus on the use of radio observatories, observations with which allow both precise localisation of events and out best estimate of the kinetic feedback from stellar explosions and accretion events.

In order to optimise this science, we pushed forward the state of the art in the response of radio telescopes to such transient astrophysical phenomena. A key aspect of this included the 'roboticisation' of the AMI-LA radio telescope, creating a mode in which the telescope responded rapidly to events detected and reported by orbiting space observatories. The whole signal chain, from X-ray detection in orbit, to radio follow up, occurs with no human intervention. This programme was backed up by a large ad-hoc programme of further high-cadence observations with this and other telescopes. In parallel, the 4 PI SKY team co-led programmes to observe such phenomena with next-generation radio telescopes such as LOFAR and MeerKAT. Core software developments led to the creation of the 4 PI SKY VOevent broker, which is a publicly-available resource used as both an information relay and triggering mechanism for world class facilities such as GAIA, HESS, ATCA.

The progamme led to many scientific breakthroughs, including:

- Discovery of the first blind-field low-frequency radio transient with the LOFAR radio telescope (origin unknown! Stewart, Fender et al. 2016)

- First radio detection of the 'thermal' Tidal Disruption Event (when a supermassive black hole tears a star apart and devours half of it; van Velzen, Anderson et al., Science, 2016)

- Discovery of very early-time radio emission from a GRB (the most relativistic flows in the present-day universe; Anderson et al. 2014)

- Discovery of extremely strong (outburst limiting) disc winds from the black hole V404 Cyg (a new, key, insight into how matter 'accretes' onto black holes; Munoz Darias et al., Nature, 2016)

- By far the most comprehensive radio coverage of jet formation and particle acceleration in an outbursting black hole every performed - following the publication of this paper we will release the entire data set as a legacy product to the community (Fender et al. in prep)

- Involvement via both the LOFAR and MeerKAT radio telescopes in the electromagnetic follow up of the first detected gravitational wave bursts (a major breakthrough - see press releases of Oct 16, 2017)

The legacy of this project is a significant push on the boundaries of our knowledge and understanding of kinetic feedback from stellar explosions, relativistic accretion onto black hole and neutron stars, and related explosive and transient phenomena. This scientific push has been suppported by innovative technological and algorithmic advances which will be important for next-generation facilities such as LSST and the SKA.