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The Transient Radio Sky to be Revealed by the SKA

Jim Cordes Cornell University AAS Meeting Washington, DC 8 January 2002. The Transient Radio Sky to be Revealed by the SKA. TRANSIENT SOURCES. Sky Surveys: The X-and- -ray sky has been monitored highly successfully with wide FOV detectors (e.g. RXTE/ASM, CGRO/BATSE).

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The Transient Radio Sky to be Revealed by the SKA

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

  2. TRANSIENT SOURCES Sky Surveys: 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.

  3. 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/0102301) • Planetary magnetospheres & atmospheres • Maser spikes • ETI

  4. Phase Space for Transients: SpkD2 vs. W W = light travel time brightness temperature: SpkD2 Tb = ------------- 2k (W)2 Pulse Spk W log SpkD2 W Process log W

  5. Phase Space for Transients: SpkD2 vs. W Pulse Lines of constant brightness temperature Spk W log SpkD2 W Process log W

  6. Phase Space for Transients: SpkD2 vs. W Pulse Solar system + local galactic sources Spk W log SpkD2 W Process log W

  7. Phase Space for Transients: SpkD2 vs. W Pulse OH masers + Pulsars (including giant pulses) Spk W log SpkD2 W Process log W

  8. Phase Space for Transients: SpkD2 vs. W Pulse Cosmological sources: AGNs (including IDV sources) + GRB afterglows Spk W log SpkD2 W Process log W

  9. Phase Space for Transients: SpkD2 vs. W Pulse Spk W log SpkD2 W Process log W

  10. Phase Space for Transients: SpkD2 vs. W Pulse Interstellar scintillations = apparent fast variations of IDVs & GRBs Spk W log SpkD2 W Process log W

  11. The SKA will thoroughly explore this phase space Pulse Spk W log SpkD2 W Process log W

  12. 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 absorption events

  13. 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? • Intermittent ETI signals? • Planetary flares?

  14. Crab Pulsar

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

  16. M33 Beam 2

  17. J1907+0918 226 ms DM = 358

  18. 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

  19. 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.

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

  21. 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

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