transients - stfc
TRANSCRIPT
The Transient Universe with The Square Kilometre Array
Rob Fender (Oxford)
On behalf of the SKA Transients Science Working Group
Extreme Astrophysics
● Collapsing stars, relativistic remnants● Extremes of density, pressure, gravitational
curvature● Searchlights
shining over cosmological distances – counterparts to LIGO events?
Two flavours of radio transients
Incoherent synchrotron emission
Relatively slow variabilityBrightness temperature limitedAssociated with all explosive events
Find these (mostly) in images
Coherent emission
Relatively fast variabilityHigh brightness temperature
Often highly polarisedSometimes very steep spectra
Find these (mostly) in time series
Early branch in classification
pipelines
Headline “known” science
Tidal Disruption Events
Accretion of matter from tidally disrupted star – very rapid increase in accretion rate onto SMBH
Fast Radio Bursts
Coherent radio bursts at cosmological distances
Probe missing baryons, act as cosmic rulers , intergalactic turbulence
Thornton et al.
We're finding new, unexplained, things....
~10 Jy ~10 minute transient at 60 MHz
Discovered a year 'late' | Doesn't repeat | No optical counterpart
From radio alone could be anything from flare star to scattered FRB
Implies ~100s/day with SKA-Low
→ highlights the need for early discovery and rapid response
(Stewart et al. in prep)
Predicted rates for SKA(assuming 100% efficient commensal)
Tidal Distruption EventsGHz (MID & SURVEY): ~1 / week
Fast Radio BurstsGHz (MID & SURVEY: ~ 1 / day)MHz (LOW): lots?? none??
Low frequency “Stewart” transientsMHz (LOW): 100s/day?
Life is full of surprises... make sure you're ready for them
This person missed a Nobel-prize transient because she wasn't set up to look for it...
Cordes et al. …. Pietka, Fender & Keane (in prep)
Be prepared, explore the unknown
timescale
luminosity
SWG recommendations
Top two recommendations from the Transients SWG for the SKA1 design:
● Commensal Transient Searches
● Rapid (robotic) Response to Triggers
Commensal Transient Searches
● Single highest priority for Transients● Increases rate of events by at least one order of magnitude● Need to follow up fast: report widely, globally and rapidly● Cost to implement much less than scale of re-/de-scopes
being currently considered (30%)● Not implementing is more damaging than scrapping an
entire SKA1 component● Politics are surmountable
Input to Science Prioritisation i
Precision Cosmology with Impulsive Radio Bursts
● The detection and localisation of N>1000 coherent bursts at cosmological distances will directly locate the missing baryons in intergalactic space that constitute at least 50% of the present-day Universe's baryonic content and determine their association with galaxy and cluster halos. As cosmological rulers, these bursts measure the curvature of the Universe with sufficient precision to determine the dark energy equation of state at redshifts > ~ 2.
Input to Science Prioritisation ii
New Physics using Ultra-Luminous Cosmic Explosions
● Ultra-luminous cosmic explosions, such as tidal disruption events and gamma-ray bursts, are the sites of the most extreme astrophysics in the universe, allowing us to probe pressures, energy and matter densities, speeds and gravitational curvature far in excess of anything we will ever achieve in a laboratory. They represent the most extreme environments since the Big Bang.
Input to Science Prioritisation iii
Black hole accretion, growth and feedback● The often-bursty radio emission from the jets of
black holes allows us to probe the kinetic feedback from black holes as a function of accretion rate, black hole mass and other observables; these are key factors in understanding how feedback affects galaxy growth. In parallel we can test theoretical paradigms such as whether or not black hole spin, or simply accretion, powers such jets.
Input to Science Prioritisation iv
Electromagnetic Counterparts to GW Events● Discovery of the electromagnetic counterparts
of gravitational wave sources would be a major breakthrough and vital in understanding their origin (e.g. merging neutron stars, black hole merger rates), especially in the case that the gravitational wave and electromagnetic signal provided two completely independent distance measurements on cosmological scales.
Multimessenger synergies
Optical, Particle, GW transients – all contemporaneous with SKA
The SKA Transients Science Working Group
● Goal: optimise SKA for transients and variables● Chairs: Fender and Macquart● Core membership: Trott, Bignall, Stappers, Law, Deller, Chatterjee,
Murphy, Corbel, Hessels, Paragi, Karastergiou, Woudt, Rupen● Advisors: Keane, Hallinan, Buitink, Swinbank, Armstrong, van
Leeuwen, Miller-Jones, Lazio, Siemion, Kuulkers, Perez-Torres, Morrison, Grainge, Agudo, Wu, Rushton, Wilkinson, Croft, Wang, Yu, Ghirlanda, Burlon, Rossi, Donnarumma, Wijers
Open to requests to join from community
In particular only UK involvement Oxford and Manchester currently
Summary
● Transients SWG wants fully commensal searches with global public events and rapid response modes as main technical change to SKA1 design. Stay flexible!
● Driven by key science of (i) FRB cosmology, (i) Cosmic explosions and extreme astrophysics, (iii) black hole growth and feedback, (iv) EM counterparts of GW transients
● We are open to new members, you can email:
[email protected] and/or