The Transient Radio Sky to be Revealed by the SKA Jim Cordes Cornell University AAS Meeting Washington, DC 8 January 2002

TRANSIENT SOURCES Sky Surveys: The X-and-  -ray sky has been monitored highly successfully with wide FOV detectors The X-and-  -ray sky has been monitored highly successfully with wide FOV detectors (e.g. RXTE/ASM, CGRO/BATSE). Neutrino/gravitational wave detectors are ‘all sky.’ The transient radio sky (e.g. t < 1 month) is largely unexplored. New objects/phenomena are likely to be discovered as well as predictable classes of objects.

TRANSIENT SOURCES (2) TARGET OBJECTS: Atmospheric/lunar pulses from neutrinos & cosmic rays Accretion disk transients (NS, blackholes) Neutron star Magnetospheres Supernovae Gamma-ray burst sources Brown dwarf flares (astro-ph/ ) Planetary magnetospheres & atmospheres Maser spikes ETI

Phase Space for Transients: S pk D 2 vs. W W W Pulse Process S pk log S pk D 2 log W W = light travel time brightness temperature: S pk D 2 T b = k ( W ) 2

Phase Space for Transients: S pk D 2 vs. W W W Pulse Process S pk log S pk D 2 log W Lines of constant brightness temperature

Phase Space for Transients: S pk D 2 vs. W W W Pulse Process S pk log S pk D 2 log W Solar system + local galactic sources

Phase Space for Transients: S pk D 2 vs. W W W Pulse Process S pk log S pk D 2 log W OH masers + Pulsars (including giant pulses)

Phase Space for Transients: S pk D 2 vs. W W W Pulse Process S pk log S pk D 2 log W Cosmological sources: AGNs (including IDV sources) + GRB afterglows

Phase Space for Transients: S pk D 2 vs. W W W Pulse Process S pk log S pk D 2 log W

Phase Space for Transients: S pk D 2 vs. W W W Pulse Process S pk log S pk D 2 log W Interstellar scintillations = apparent fast variations of IDVs & GRBs

The SKA will thoroughly explore this phase space W W Pulse Process S pk log S pk D 2 log W

TRANSIENT SOURCES (3) TARGET PROCESSES: Intrinsic: incoherent: (  inverse Compton brightness limit) coherent: (virtually no limit) continuum: low frequencies favored spectral line: masers Extrinsic: scintillation maser-maser amplification gravitational lensing absorptionevents

TRANSIENT SOURCES (4) Sure detections: Analogs to giant pulses from the Crab pulsar out to ~5 – 10 Mpc Flares from brown dwarfs out to at least 100 pc. GRB afterglows to 1 µJy in 10 hours at 10 . Possibilities:  -ray quiet bursts and afterglows?  -ray quiet bursts and afterglows? Intermittent ETI signals? Intermittent ETI signals? Planetary flares? Planetary flares?

Crab Pulsar

Giant Pulses from Nearby Galaxies SCIENTIFIC RETURN Many objects  map out IGM as well as ISM of Many objects  map out IGM as well as ISM of galaxies galaxies IGM: electron density and magnetic field IGM: electron density and magnetic field NS birth rates in other galaxies NS birth rates in other galaxies Constraints on IMF Constraints on IMF Census of young pulsars, clues about magnetars? Census of young pulsars, clues about magnetars?

M33 Beam 2

J ms DM = 358

Working Around Radio Frequency Interference Single-dish/single-pixel transient detection: – Very difficult to separate terrestrial & astrophysical transients (significant overlap in signal parameter space) Multiple beam systems (Parkes, Arecibo, the GBT): –Simultaneous on/offs  partial discrimination Multiple site systems (a la LIGO, PHOENIX) –Very powerful filtering of RFI that is site specific or delayed or Doppler shifted between sites

Methods with the SKA I. Target individual SNRs in galaxies to 5-10 Mpc II. Blind Surveys: trade FOV against gain by multiplexing SKA into subarrays. III. Exploit coincidence tests to ferret out RFI, use multiple beams.

Primary beam & station synthesized beams Station subarrays for larger FOV (mosiacing) One station of many in SKA

Summary Transient science is unexplored territory for radio astronomy: New looks at known sources, entirely new classes of sources: LOFAR will survey transients at f < 240 MHz; SKA for 240 MHz < f < 22 GHz (or more) Implications for SKA design: Rapid imaging/mosaicing of sky (days) Large instantaneous FOV desired for short time scales (e.g. hemispheric). US Plan: Subarrays to allow coincidence tests and maximal sky coverage. Versatile imaging/beamforming/signal processing modes. Similar implications from pulsar science