23 june 2005jim cordes: ska: pulsars and gravity the square kilometer array: discovery and timing of...
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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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23 June 2005 Jim Cordes: SKA: Pulsars and GravityJim Cordes: SKA: Pulsars and Gravity
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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23 June 2005 Jim Cordes: SKA: Pulsars and GravityJim Cordes: SKA: Pulsars and Gravity
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
23 June 2005 Jim Cordes: SKA: Pulsars and GravityJim Cordes: SKA: Pulsars and Gravity
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
23 June 2005 Jim Cordes: SKA: Pulsars and GravityJim Cordes: SKA: Pulsars and Gravity
23 June 2005 Jim Cordes: SKA: Pulsars and GravityJim Cordes: SKA: Pulsars and Gravity
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
23 June 2005 Jim Cordes: SKA: Pulsars and GravityJim Cordes: SKA: Pulsars and Gravity
Surveys: past, present and future
23 June 2005 Jim Cordes: SKA: Pulsars and GravityJim Cordes: SKA: Pulsars and Gravity
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
23 June 2005 Jim Cordes: SKA: Pulsars and GravityJim Cordes: SKA: Pulsars and Gravity
, , 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
23 June 2005 Jim Cordes: SKA: Pulsars and GravityJim Cordes: SKA: Pulsars and Gravity
The power of ALFA:
I(, t, j) j=1,7
23 June 2005 Jim Cordes: SKA: Pulsars and GravityJim Cordes: SKA: Pulsars and Gravity
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
23 June 2005 Jim Cordes: SKA: Pulsars and GravityJim Cordes: SKA: Pulsars and Gravity
Comparison of maximum detectable distance vs. P and pulsar luminosity
23 June 2005 Jim Cordes: SKA: Pulsars and GravityJim Cordes: SKA: Pulsars and Gravity
23 June 2005 Jim Cordes: SKA: Pulsars and GravityJim Cordes: SKA: Pulsars and Gravity
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
23 June 2005 Jim Cordes: SKA: Pulsars and GravityJim Cordes: SKA: Pulsars and Gravity
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)
23 June 2005 Jim Cordes: SKA: Pulsars and GravityJim Cordes: SKA: Pulsars and Gravity
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
23 June 2005 Jim Cordes: SKA: Pulsars and GravityJim Cordes: SKA: Pulsars and Gravity
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
23 June 2005 Jim Cordes: SKA: Pulsars and GravityJim Cordes: SKA: Pulsars and Gravity
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++
23 June 2005 Jim Cordes: SKA: Pulsars and GravityJim Cordes: SKA: Pulsars and Gravity
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
23 June 2005 Jim Cordes: SKA: Pulsars and GravityJim Cordes: SKA: Pulsars and Gravity
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
23 June 2005 Jim Cordes: SKA: Pulsars and GravityJim Cordes: SKA: Pulsars and Gravity
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
23 June 2005 Jim Cordes: SKA: Pulsars and GravityJim Cordes: SKA: Pulsars and Gravity
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)?
23 June 2005 Jim Cordes: SKA: Pulsars and GravityJim Cordes: SKA: Pulsars and Gravity
Discussion IssuesDiscussion Issues
• 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?
23 June 2005 Jim Cordes: SKA: Pulsars and GravityJim Cordes: SKA: Pulsars and Gravity
Discussion IssuesDiscussion Issues
• 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)