The Dynamic Radio Sky and Future Instruments Jim Cordes Cornell University AAS Meeting Nashville 28 May 2003

Dynamic Radio Sky We know enough about the DRS to know that there is a great deal yet to be discovered c.f. the high energy universe, optical, etc. What is in the DRS? What are the prospects for new discoveries? Astrophysical parameters Extrinsic effects RFI Instruments & surveys that will reveal the DRS

TRANSIENT SOURCES Sky Surveys: The X-and-  -ray skies have been monitored highly successfully with wide FOV detectors The X-and-  -ray skies have been monitored highly successfully with wide FOV detectors (e.g. RXTE/ASM, CGRO/BATSE). Neutrino/gravitational wave detectors are ‘all sky.’ Optical transient surveys (ROTSE, RAPTOR, LSST) are/will revolutionalize our knowledge of the optical transient sky and will drive the trend toward data mining of » petabyte databases. The transient radio sky (e.g. t < 1 month) is largely unexplored. New objects/phenomena are likely to be discovered as well as extreme cases in predictable classes of objects.

Ingredients for transient detection A  T needs to be “large” A = collecting area  = solid angle covered (instantaneous FOV) T = time per sky position Issue: to dwell (stare), or tile the sky, or be triggered?

Successes in transient astronomy RXTE/ASM Vela ROTSE RAPTOR

Why is the Dynamic Radio Sky Largely Uncharted? Large collecting areas, A, needed for sensitivity Typically A  is small enough that telescope throughput is small Telescope time is expensive so dwell times are short Sources cover a wide range of time scale and sky density  insufficient sky and temporal coverage

Giant pulse from the Crab pulsar S ~ 160 x Crab Nebula ~ 200 kJy Detectable to ~ 1.5 Mpc with Arecibo Arecibo 2-ns giant pulses from the Crab: (Hankins et al. 2003) Giant Pulses seen from B in LMC (Johnston & Romani 2003)

Giant pulses are the fastest known transients Giant pulses from Crab detectable to ~1.5 Mpc with 1/hour 2-ns wide `nano-Giant pulses’ identified from Crab (Hankins et al. 2003) GPs seen from Crab clone in LMC (B ) by Johnston & Romani (2003) w/ similar intrinsic amplitude GPs from two millisecond pulsars Radio GPs in pulse components also seen in X-rays GP-emitting objects have ~ same B fields at their light cylinders

Nano-giant pulses (Hankins et al. 2003) Arecibo 5 GHz 0.5 GHz bw coherent dedispersion

STARE 611 MHz 3-station radio transient detector (Katz, Hewitt, Corey, Moore 2003) Solar Radio Bursts

GRB variability (Frail et al. 2000) Interstellar scintillations

TRANSIENT SOURCES 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

TRANSIENT SOURCES 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

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

New instruments can cover this phase space W W Pulse Process S pk log S pk D 2 log W

Exploring the Transient Radio Sky: Striving for large A  T Pilot observations: Arecibo: single pixel and multibeam (ALFA) STARE and similar multisite arrays GBT: single pixel and multibeam arrays ATA: 2.5 deg FOV, ~8 array beams EVLA (wideband, high sensitivity & spatial resolution) LOFAR: low frequencies (< 240 MHz) SKA: broad frequency range (0.15 to 25 GHz)

Giant pulses from M33 Arecibo observations (Maura Mclaughlin & Cordes, submitted to ApJ, astro-ph

Galactic Center Transients VLA 0.33 GHz Hyman et al. 2002

Exploring the Transient Radio Sky: Covering the Sky Staring vs. mosaicing (tiling)? Radio sky needs both; Fast transients: too fast to raster scan the sky (< hours to months) (e.g. GPs) Slower transients: raster scan (e.g. for objects showing radio only) trigger from other wide-field instruments (GRB afterglows)

TRANSIENT SOURCES 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?

Isolated pulsar Re-ignition of pulsar action in mergers? Hansen & Lyutikov 2000

RFI Editing in the f-t plane RFI dynamic spectra (from AO monitoring program) Dynamic spectrum of pulsar scintillation

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

LOFAR = Low Frequency Array Stations of dipoles 30 to 240 MHz Large A  T Optimal for coherent continuum transients

SKA = Square Kilometer Array Current Concepts Current Concepts China KARST Canadian aerostat US Large N Australian Luneburg Lenses Dutch fixed planar array (cf. Allen Telescope Array, Extended VLA) (cf. LOFAR = Low Freqency Array)

Current Baseline Specifications

Methods with LOFAR & SKA I. Target individual objects II. Blind Surveys: trade FOV against gain by multiplexing SKA into subarrays. III. Allow rapid response to triggers IV. Exploit coincidence tests to ferret out RFI, use multiple beams.

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

Blind Surveys with SKA Number of pixels needed to cover FOV: N pix ~(b max /D) 2 ~ Number of operations N ops ~ petaops/s Post processing per beam: e.g. standard pulsar periodicity analysis

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 0.15 GHz < f < 25 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 for pulsar science

Radio Pulsars ~1400 known (doubled by Parkes MB) ~100 millisecond pulsars 2 to 3 with planets ~5 NS-NS binaries (P orb > 8 hr) MSPs have exceedingly stable spins, suitable for seeking gravitational wave perturbations

Why more pulsars? Extreme Pulsars: P 8 sec P orb G (link to magnetars?) V > 1000 km s -1 NS-NS & NS-BH binaries Population & Stellar Evolution Issues The high-energy connection (e.g. GLAST) Physics payoff (GR, Gwaves, EOS, LIGO, GRBs…) Serendipity (strange stars, transient sources) New instruments (AO, GBT, LOFAR, SKA) will dramatically increase the volume searched (galactic & extragalactic)

Parkes MB Feeds

ALFA Science Goals: Massive Surveys Drift scan surveys (14 sec across 3.5 arcmin) Deep Galactic plane survey (GPS) (5-10min, |b| < 5 deg, 30 < l < 80 + anticenter) Medium latitude surveys ( 5 < |b| < 25 deg) Targeted: globular clusters, high EM/DM HII regions, SNRs, Galactic chimneys, M33, X/  -ray selected objects (long dwell times, up to 2.5 hr)

Surveys with Parkes, Arecibo & GBT. Simulated & actual Yield ~ 1000 pulsars.

ALFA Surveys at Arecibo ALFA surveys can be viewed as part of a long- term, grander effort (“Full Galactic Census”) (LOFAR, SKA, ) RFI mitigation required and provides general purpose tools Data & data products = long term resources  data management policy & resources ~ 1 petabyte of survey raw data ~ 1 petabyte of data products Exploit telescope time fully (transients, piggybacking)

SKA pulsar survey 600 s per beam ~10 4 psr’s