2 Oct 2007Jim Cordes Modern Radio Universe Manchester 1 Discovery frontier for + CR + GWs –Less so at high energies BATSE, RXTE/ASM, Beppo/Sax, SWIFT,

2 Oct 2007 Jim Cordes Modern Radio Universe Manchester

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Discovery frontier for + CR + GWs– Less so at high energies

• BATSE, RXTE/ASM, Beppo/Sax, SWIFT, GLAST, etc.– More so for optical, radio

GLAST: full-sky survey every three hours for 1+ yearsOptical

• PanSTARRS = Panoramic Survey Telescope and Rapid Response System• LSST (LST) = Large Synoptic Survey Telescope (rename to OSST!)• Science goals: includes transients on minute 10 yr time scales

Radio• Phase space:

– Knowns: already a very rich set – Hypotheticals

Radio Synoptic Survey Telescopes• Survey metric for transients• The mid-frequency SKA as the RSST

Axes of Discovery: the Time Variable UniverseJim Cordes, Cornell University

Heraclitus “You don’t observe the same universe twice”


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Why Radio Transients?No comprehensive survey of large phase space

• Need large AT (area, solid angle and time coverage)• ns to years• complex structures in the frequency-time plane HPC processing

Nature can produce cheap radio photons via coherent radiation processes (N2 vs N) so detectable to great distances

Fast transients are linked to extreme matter states (t < 1s)… or ETICounterparts to known source classes

• Prompt radio bursts from GRBs• Gamma-ray quiet, radio-loud GRBs

Expect new source classes (ETI, evaporating BHs, particle events)

Beacons for probing the cosmic web and fundamental constants• Intervening plasmas (IPM, ISM, IGM) dispersion, scattering, scintillation• Photon mass, charge from measured dispersion law (de Broglie 1940)


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GCRT J1745-3009 Hyman et al. 2005

Bower et al. 2005Spk ~ 80 mJy SD2 ~ 5.1 Jy kpc2 W ~ 100 d

Galactic Center Transients


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Roughly 1/3 of all psrs detected with FFT also detected in SP search Some objects detected only

in SP search Wide range of single-pulse

properties apparent Galactic pulsar population

may be much larger than previously thought

PMB Single Pulse SearchMcLaughlin et al. (2006)

PMB Single Pulse SearchMcLaughlin et al. (2006)

J1840–0815 P = 1.1 s DM = 225 pc cm-3

J1840–0809 P = 0.96 s DM = 353 pc cm-3

RRATs: rotating radio transients(Andrew Lyne’s talk)


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Pulsar Survey with Arecibo Multibeam System (ALFA)(Arecibo ~ 10% SKA)

Detection of a strong pulsar amid RFI

Detection of a weak millisecond pulsar in beam 1


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• Asteroid disk from SN fallback material

• Only ~ 10-4 Earth masses needed to provide enough material to perturb coherent radiation from a pulsar over its 10 Myr lifetime

• Asteroids evaporate at ~109 cm from the NS and trigger or quench pair production from gaps in the magnetosphere

• Expect induced torque fluctuations

astro-ph/0605145


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Artist's impression of a brown dwarf with "super-aurorae" at its magnetic poles, causing the pulsed radio emission. (Credit: Copyright National University of Ireland, Armagh Observatory, National Radio Astronomy Observatory, United States Naval Observatory & Vatican Observatory, Arizona)

Time series of the radio emission detected with the VLA from the M9 dwarf TVLM 513-46546. Every 1.958 hours a periodic pulse is detected when extremely bright, beams of radiation originating at the poles sweep Earth when the dwarf rotates.

Brown dwarf pulsationsHallinan et al. 2007


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Bursting radio emission from magnetarsCorrelated torque and radio variationsCamilo et al. 2007

1E 1547-5408

Flat spectrum (not pulsar like)


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Crab giant pulses: the highest brightness temperatures known

“nano shots”


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Frequency-time structure in a Crab Giant PulseEilek & Hankins 2006, Hankins & Eilek 2007

Arecibo data

Winedt.lnk


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Phase Space for Transients:

SpkD2 vs. W

W = pulse width or characteristic time scale


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Filling phase space with hypothetical new discoveries:

Prompt Gamma-ray emission

Evaporating black holes

Maximal giant pulse emission from pulsars

ETI’s asteriod radar

What else?


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Detection limits for the SKA:

SpkD2 >threshold

Prompt GRBs and GRB afterglows easily seen to cosmological distances

Giant pulses detectable to Virgo cluster

Radio magnetars detectable to Virgo

ET radar across Galaxy


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Lazio et al. 2003

Bastian, Dulk & Leblanc (2000)

Cyclotron maser emission Radiometric Bodes Law Desch & Kaiser 1984

Planetary Radio Emission


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W ~ 4.6 ms ( / 1.4 GHz)-4.80.4

DM ~ 375 pc cm-3

Steep spectrum (=-4)

Science Express27 Sep 2007


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Detection limits for the SKA:

SpkD2 >threshold

Prompt GRBs and GRB afterglows easily seen to cosmological distances

Giant pulses detectable to Virgo cluster

Radio magnetars detectable to Virgo

ET radar across Galaxy

Parkes SP(if D>500 Mpc)


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Prompt Radio Bursts from -ray BurstsScale from -ray fluence:

Implied flux density:

Reasonable?Compare with maximal pulsar energy losses

Can radiation get out? (Macquart 2007)Induced Compton and Raman scattering

Long bursts: hypernovae dense plasma from pre-SN stellar wind, immersed in SF region perhaps no emergent radio emissionmitigating effect: radio coherent, upboosted photons incoherent

Short bursts: merging NS-NS, NS-BH vacua that high-brightness radiation can get through plausible radio bursts through reactivation of magnetosphere

n+1 ~ 3.5


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Isolated pulsar Re-activation of pulsar action in mergers?

Hansen & Lyutikov 2000

Lyutikov 2006


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Transient Surveys• Fast

• Too fast to be sampled by raster scanning (<1 day)• Sub-second transients:

– Produced by compact sources (size < ct)– Coherent radiation– Influenced by diffractive interstellar scintillations

imposed -t structure on intrinsic signal• Sampled by “staring” for long dwell times• Large solid angle coverage needed for rare events

– Likelihood of detection– Completeness level

• Very high data rates for full FoV analysis

• Slow • Durations long enough to be handled with imaging raster

scans


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Survey Metrics“Survey speed” for Steady Sources:

• Payoff = number of objects detected to some flux density level in some fixed amount of time

• Steady sources, homogeneously distributed, etc.» Integration time per source = dwell time in survey

• Get same metric by looking at rate at which volume or solid angle surveyed:

SS = FoV (A/T)2

• Processed bandwidth enters in linearly SS = FoV (A/T)2 B

• Extended survey metric that includes other factors:fc = fraction usable antennas

NFoV = number of pixels (PAFs) Nsa = number of subarrays

m = signifcance level (min. S/N)


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Survey MetricsSurvey speed for Transient Sources:

• W = transient duration, = dwell time in survey scan• Slow transients: integration time = • Fast transients: (days ns) integration time = W New factor on survey metric that accounts for

integration time and time-capture probability

FoMTS = FoMSS integration time factor Pt

Integration time factor

Probability that 1 event occurs from source when pointed ata = W, = event rate/sourcex = / W

K(a,x) 1

See SKA memo by JMC to appear at www.skatelescope.org


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For:

1 GHz

1 sec integration

0.3 GHz bw

25 K, 60%

Sensitivity vs. instantaneous FoV

$$$$$$$

¢¢¢¢¢


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Wide FoV Non-Imaging Surveys

• Pixelization of the field of view• Correlation approach favored over beam forming• Number of pixels

• Sky coverage• Raster scanning (slow transients)• Staring (fast transients)

• Analysis• Full search analysis on each pixel • Extensive for pulsars and fast transients

– E.g. 1024 frequency channels 64 s samples from each pixel

• Frequency-time plane analysis for all cases to discriminate RFI from celestial signals


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Example Synoptic Cycle for SKAA 10-day total cycle: variable scanning rates

– Fast for extragalactic sky (away from Galactic plane)E.g.• 1 deg2 single pixel FoV• Full sky survey (80% of 40,000 deg2)• Tscan = 5 days• T ~ 10 sec = time per sky position• Smin ~ 15 Jy at 10 with full sensitivity and on axis• Multiple pixel systems (PAFs) increase sensitivity (for fixed total time)• Subarrays reduce sensitivity but speed up the survey

– Slow for deep extragalactic fields and Galactic plane– Galactic center: staring mode– Repeat scans many times– Break out of scanning mode for targeted observations (10%?)– Break out for targets of opportunity

Issues for pulsars (~steady amplitudes):– Need minimum contiguous dwell time for Fourier transforms (e.g. 100 – 1000 s

for large-area blind surveys)– Need frequent re-observation coverage for long-term timing followup

Calibration requirementsAre there solutions for HI, pulsars, transients, SETI and magnetism?

– Yes (to zeroth order)


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Summary• A complete inventory requires attention to the time domain on many

scales• A multi-wavelength enterprise but some radio-unique areas too• Target classes for transients

• Relativistic objects (stellar, AGN)• Planets, brown dwarfs• ETI• Evaporating black holes? What else?

• Keys to discovery at radio wavelengths • Time-frequency (t-) analysis• Wide-field sampling ()• Low-mid-high sensitivity (smin)

• Blind surveys of the radio sky• Expand AeT• Comprehensive matched filtering (computing)• Start now

Arecibo, GBT, Parkes,WSRT,EVLA ATA,LOFAR, LWA,MWA,ASKAP,MeerKAT SKA

• Fast transients: obtain & process data as in pulsar surveys, SETI +?• Slow transients: raster scan the sky repetitively• Develop the SKA as a Radio Synoptic Survey Telescope (RSST)

Causes:• internal instabilities• extrinsic triggers• external modulations

• lensing• scintillations


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Extra Slides


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Arecibo/ALFA (30% of sky in 2000 hr)

or

SKA/SP (80% of sky in 5 days)

SKA/PAF (80% of sky in 5 days)

low rate

high rate

“W” limited


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Science and Implementation of RSST• SKA mid-frequencies: 0.3 to >3 GHz

• Hydrogen 0.3 – 1.4 GHz» (galaxy evolution, dark energy)

• Pulsars and Gravity » (GR, GWaves, EoS, Magnetospheres) ~0.8 – 3 GHz

• Transients (ns to years) 0.3 – 8 GHz» Relativistic objects» Exoplanets» SETI

• Magnetic Universe 1 – 2 GHz

• Synoptic and Commensal Surveys• Sensitivity + Wide FoV + Frequency-time flexibility• Spectral line + pseudo-continuum + time-domain surveys• Need multiple backend processors• Compatibility issues (configuration, cadences, scan types)

» HI galaxy evolution ~10 km baselines» Pulsar/transient full-FoV search < 1 km


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Small and Big Science

• Discovery space can be explored with both low sensitivity and high sensitivity instruments

• W space: ns years space: MHz -rays• rate space: >>1 s-1 to 1 d-1 hemisphere-1

• flux densities: Jy to GJy

• Fast transients require matched filtering in the -t plane • High-resolution, high-performance processing

• Minimal systems can make useful observations• Low-f: LOFAR, LWA, MWA• Mid-f: Arecibo, GBT, EVLA, ATA, ASKAP, MeerKAT• High-f: GBT, EVLA, ALMA?

Documents

2 Oct 2007Jim Cordes Modern Radio Universe Manchester 1 Discovery frontier for + CR + GWs –Less so at high energies BATSE, RXTE/ASM, Beppo/Sax, SWIFT,