23 June 2005Jim Cordes: SKA: Pulsars and Gravity The Square Kilometer Array: Discovery and Timing of Pulsars Jim Cordes, Cornell University The SKA Project

23 June 2005 Jim Cordes: SKA: Pulsars and GravityJim Cordes: SKA: Pulsars and Gravity

The Square Kilometer Array:The Square Kilometer Array: Discovery and Timing of Pulsars Discovery and Timing of Pulsars

Jim Cordes, Cornell UniversityJim Cordes, Cornell University

• The SKA Project• SKA science case

• Fundamental questions in physics, astrophysics and astrobiology

• Unprecedented capacity for discovery

• International and US activity• The Pulsar Key Science Project

• Massive census of the Galaxy, globular clusters and nearby galaxies

• Generalized search algorithms• Issues for precision timing

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SKA: What is It?SKA: What is It?• An array telescope that combines complete

sampling of the time, frequency and spatial domains with a 20 to 50 increase in collecting area (~ 1 km2) over existing telescopes.

• Frequency range 0.1 – 25 GHz (nominal)• Limited gains from reducing receiver noise or

increasing bandwidth once the EVLA is finished• Innovative design needed to reduce cost

• 106 meter2 ~ €1,000 per meter2

• c.f. existing arrays ~ €10,000 per meter2

• An international project from the start• International funding

• Cost goal ~ € 1 billion• 17-country international consortium

• Executive, engineering, science, siting, simulation groups

• Timeline for construction extends to 2020• Can be phased for different frequency ranges• Can do science as you build

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Science with the Square Kilometer ArrayScience with the Square Kilometer Array

edited by edited by Chris CarilliChris Carilli

Steve RawlingsSteve Rawlings

Special issue of New Astronomy ReviewsSpecial issue of New Astronomy ReviewsVolume 48, December 2004, 979-1605Volume 48, December 2004, 979-1605

(48 chapters)(48 chapters)

• Five key science projects

• Discovery science

• Enabling understanding in fundamental physics and origins


Five Key Science Areas for the SKAFive Key Science Areas for the SKATopic Goals

Probing the Dark Ages

1. Map out structure formation using HI from the era of reionization (6 < z < 13)

2. Probe early star formation using high-z CO

3. Detect the first active galactic nuclei

Gravity: Pulsars & Black Holes

1. Precision timing of pulsars to test theories of gravity approaching the strong-field limit (NS-NS, NS-BH binaries, incl Sgr A*)

2. Millisecond pulsar timing array for detecting long-wavelength gravitational waves

Cosmic Structure1. Understand dark energy [e.g. eqn. of state; W(z)]

2. Understand structure formation and galaxy evolution

3. Map and understand dark matter

Cosmic MagnetismDetermine the structure and origins of cosmic magnetic fields (in galaxies and in the intergalactic medium) vs. redshift z

The Cradle of Life

1. Understand the formation of Earth-like planets

2. Understand the chemistry of organic molecules and their roles in planet formation and generation of life

3. Detect signals from ET



Other ReferencesOther References

“Strong-field tests of gravity using pulsars and black holes,” Kramer et al. 2004

“Pulsars as tools for fundamental physics and astrophysics,” Cordes et al 2004

In Science with the Square Kilometer Array,Eds. C. Carilli and S. Rawlings (~50 articles)Available at www.skatelescope.org and on

arXiv/astro-ph

http://www.skatelescope.org/


Surveys: past, present and future


Was Einstein Right About Gravity?Was Einstein Right About Gravity?The SKA as a Pulsar/Gravity MachineThe SKA as a Pulsar/Gravity Machine

• Relativistic binaries (NS-NS, NS-BH) for probing strong-field gravity

• Orbit evolution + propagation effects of pulsars near Sgr A*• Millisecond pulsars < 1.5 ms (EOS)• MSPs suitable for gravitational wave detection• 100s of NS masses (vs. evolutionary path, EOS, etc)• Galactic tomography of electron density and magnetic field;

definition of Milky Way’s spiral structure• Target classes for multiwavelength and non-EM studies (future

gamma-ray missions, gravitational wave detectors)

Blue points: SKA simulationBlack points: known pulsars

Millisecond PulsarsMillisecond Pulsars Relativistic BinariesRelativistic Binaries

Today TodayFuture

SKASKA SKASKA

Future

only 6!~104 pulsar detections


, , t, pol, , t

Large processing FOV

High sensitivity:

Combine Greater Sensitivity with Wide Field of View ProcessingCombine Greater Sensitivity with Wide Field of View Processing

The SKA combines a > 20 boost in sensitivity with unprecedented utilization of the field of view

23 June 200523 June 2005 Jim Cordes: SKA: Pulsars and GravityJim Cordes: SKA: Pulsars and Gravity

Pulsar Periodicity SearchPulsar Periodicity Search

time

Fre

quen

cy

time

DM

|FFT(f)|

FFT each DM’s time series

1/P 2/P 3/P


The power of ALFA:

I(, t, j) j=1,7


A pulsar found A pulsar found through its single-through its single-pulse emission, not its pulse emission, not its periodicity (c.f. Crab periodicity (c.f. Crab giant pulses).giant pulses).

Algorithm: matched Algorithm: matched filtering in the DM-t filtering in the DM-t plane.plane.

ALFA’s 7 beams ALFA’s 7 beams provide powerful provide powerful discrimination discrimination between celestial and between celestial and RFI transientsRFI transients


Comparison of maximum detectable distance vs. P and pulsar luminosity



SKA Development in the USSKA Development in the USUS Concept: Large-N/Small-D (LNSD)• The US SKA Consortium prepares whitepapers on the LNSD concept

for consideration by the International SKA Steering Committee and also for a SW US high-frequency SKA site

• Allen Telescope Array• Low-frequency arrays (MWA, LWA) = science and technology

precursors • Deep Space Network Array: closely related to US SKA concept, strong

possibilities for economies of scale• Explicit SKA development:

• NSF ATI Grant: ($1.5M) 2002-2005• Technology Development Project (TDP)

» $32M over 5 years (NSF proposal pending)» End to end development, costing, preliminary design» Organized through the US SKA Consortium (17 institutions)» Managed by NAIC/Cornell» Facilitates and unifies SKA development at NRAO, NAIC, and institutions

involved with low-frequency array development


Siting the SKASiting the SKA• Current siting decision is late 2006 (ISPO)

• Argentina, Australia, China, South Africa: proposals expected by end of 2005

• Working plan: single site for all frequencies, covered with 2 to 3 antenna technologies (subject to optimization vs. cost/performance)

• Dipoles ≤ 0.3 GHz• Aperture array 0.3 ≤ ≤ 2 GHz• Paraboloids 1 ≤ ≤ 25 GHz

• US perspective:• SKA low-frequency array in southern hemisphere

» radio quiet zone ≤ 2 GHz

• SKA high-frequency array built upon the EVLA+VLBA» Better tropospheric properties than southern sites, RFI less an issue» leverages existing investments» recognizes international utilization of EVLA, VLBA

• Proposed by the US SKA Consortium to the International SKA Steering Committee as a Discussion Document (2005 April)


Issues for SKA Searching and TimingIssues for SKA Searching and Timing• Collecting area needs a significant fraction in a compact core

array to allow wide FOV searches with acceptable data rates (10 yr from now!)

• Beam forming + pulsar search analysis in > 104 pixels• ~ 1015 op s-1 (scales with diameter2 of core array)

• Need high-frequency capability to search/time pulsars in the star cluster around SgrA*

• Interstellar multipath: d ~ 300 s -4 ( in GHz) 10 to 15 GHz (higher?) c.f. pulsar steep spectra, but some are ~flat

• Timing: above a single-pulse S/N ~ few, timing precision is determined by factors other than S/N:

• Single pulse amplitude and phase fluctuations• Interstellar scattering effects• Polarization calibration

• So many pulsars to time!• need to exploit multiple beaming capability of a large scale, distributed

array or time only the best objects

All can be mitigated to some extent


Blind Surveys with SKABlind Surveys with SKA• Number of pixels needed to cover

FOV: Npix~(bmax/D)2

~104-109

• Number of operationsNops~ petaop/s

• Post processing per beam:single-pulse and periodicity analysis Dedisperse (~1024 trial DM values) +

FFT + harmonic sum (+ orbital searches + RFI excision)

• Correlation is more efficient than direct beam formation

• Requires signal transport of individual antennas to correlator

(pulsars, transients, ETI)

≥104 beams needed

for full-FOV sampling


Sampling the pulsar luminosity function Sampling the pulsar luminosity function in Sgr A* and other galaxiesin Sgr A* and other galaxies

Pulsar detectability with the SKA for GC pulsars and extragalactic pulsars

High frequencies are needed for searches of the Galactic Center owing to intense radio wave scattering

GC = GC++


Pulsar Astrometry with the SKAPulsar Astrometry with the SKA• Pulse timing models and reference frame definition• Proper motions and parallaxes for objects across the

Galaxy monitoring programs over ~ 2 yr/pulsar• Optimize steep pulsar spectra against -dependence of

ionospheric and tropospheric and interstellar phase perturbations ( 2 to 8 GHz)

• In-beam calibrators (available for all fields with SKA)• 10% of A/T on transcontinental baselines implies 20

times greater sensitivity over existing dedicated VLB arrays


Pulsar TimingPulsar TimingIssues:• Spin stability of NS (spin noise)

• Spin rate• Orientation effects (precession)• Glitches

• Stability of the radiation beam “attached’’ to the spinning NS

• Beam wavering from precession• Pulse amplitude and phase jitter (radiation coherence

effects)

• Effects on propagating pulses by the intervening ISM (plasma effects)

• Time tagging of measured pulses


Mitigation of TOA Estimation ErrorsMitigation of TOA Estimation Errors• Polarization purity

• need -40dB accuracy after hardware and post processing across the entire FOV used for timing

• Pulse amplitude/phase jitter limitations on optimality of matched filtering• Error-correction algorithms: use correlations of pulse shape

perturbation with TOA perturbation (unpublished)

• Electron density fluctuations in the ISM • 103 km to > pc (~Kolmogorov) DM(t) … correctable• Time-variable pulse-broadening function … partly correctable

– Secular (months, years): refractive modulation N effects from finite number of scintles in the f-t plane

• Time-variable angle of arrival– Refraction from large-scale structures in the ISM


Discussion IssuesDiscussion Issues

• Pulsar timing precision: how to improve?• Choice of frequency vs. pulsar

• State of the art polarization calibration

• DM(t), scintillation corrections

• Error correction for intrinsic pulse fluctuations

• Pulsar array:• Large N of pulsars vs. pulsars of opportunity (small N)?



• Design and usage issues for the SKA• Size of core array usable for searching

• Polarization calibration across wide FOV

• How to deal with the huge number of new pulsars:– Time only the best after initial quick assessment?

– Require multibeam capability?



• Astrofinance and politics:• Need to jointly promote gravity studies:

– Laboratory and spacecraft gravitational wave detectors

– Pulsars as clocks and gravitational laboratories

• Sometimes perceived as having no connection and/or in competition

• Joint SKA and LISA meeting? (Kramer)

Documents

23 June 2005Jim Cordes: SKA: Pulsars and Gravity The Square Kilometer Array: Discovery and Timing of Pulsars Jim Cordes, Cornell University The SKA Project