Fundamental Physics and Astrophysics using Pulsars and the SKA

1
Fundamental Physics andAstrophysicsusingPulsa
rs and the SKA
Jim Cordes Cornell U.
Vicky Kaspi McGill U.
Michael Kramer Jodrell Bank
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Pulsar Science Highlights

• Key Science
• Strong-field Tests of Gravity
• Was Einstein Right?
• Cosmic Censorship, No-Hair Theorem
• Cosmic Gravitational Wave Background
• Variety of Other Major Astrophysical Topics
• Milky Way Structure, ISM
• Intergalactic Medium
• Relativistic Plasma Physics
• Extreme Densities
• Extreme Magnetic Fields

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Pulsars

• embody physics of the EXTREME
• surface speed 0.1c
• 10x nuclear density in centre
• some have B gt Bq 4.4 x 1013 G
• Voltage drops 1012 volts
• FEM 109Fg 1011FgEarth
• Tsurf million K
• relativistic plasma physics in action
• probes of turbulent and magnetized ISM
• precision tools, e.g.
• - Period of B193721
• P 0.0015578064924327?0.000000000000
  0004 s
• - Orbital eccentricity of J10125307
  elt0.0000008

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Noted GR Laboratories
Weisberg Taylor (priv. comm)
Hulse Taylor (1974)

• Orbit shrinks every day by 1cm
• Confirmation of existence of gravitational waves

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First Double Pulsar!
Lyne et al.(2004)

• Pb2.4 hrs, d?/dt17 deg/yr
• MA1.337(5)M?, MB1.250(5)M?

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Was Einstein right?
General Relativity vs Alternative Theories

• Strong Equivalence Principle
• Violation of Lorentz-Invariance
• Violation of Positional Invariance
• Violation of Conservation Laws etc.

Solar System tests provide constraints
but only in weak field!
No test of any theory of gravity is complete, if
only done in solar system, i.e. strong field
limit and radiative aspects need to be tested,
too!
? This is and will be done best with radio
pulsars!
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Was Einstein right?
General Relativity vs Alternative Theories

• Strong Equivalence Principle
• Violation of Lorentz-Invariance
• Violation of Positional Invariance
• Violation of Conservation Laws etc.

Binary Pulsars

• Clean strong-field tests, incl.
• Shapiro delays
• Gravitational Radiation
• Geodetic Precession

So far General Relativity has passed all tests
with flying colours!
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Exploration of Black Holes
Compact PSR Binaries
We will probe BH properties with pulsars and
SKA - precise measurements - no
assumptions about EoS or accretion physics -
test masses well separated, not deformed
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Black Hole properties
spin and quadrupole moment

• Astrophysical black holes are expected to rotate

S angular momentum Q quadrupole moment

• Result is relativistic classical spin-orbit
  coupling
• Visible as a precession of the orbit
• Measure higher order derivatives of secular
• changes in semi-major axis and longitude of
• periastron (relativistic) or transient TOA
  
• perturbations (classical)
• Not easy! It is not possible today!
• Requires SKA sensitivity!

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Cosmic Censorship No-Hair

• For BH-like companions to pulsars, we will
  measure spin precisely
• In GR, for Kerr-BH we expect

• But if we measure
• ? gt 1 ? Event Horizon vanishes
• ? Naked singularity!

GR is wrong or Censorship Conjecture violated!
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Cosmic Censorship No-Hair

• For BH-like companions to pulsars, we will
  measure spin precisely
• In GR, for Kerr-BH we expect

• But if we measure
• ? gt 1 ? Event Horizon vanishes
• ? Naked singularity!
• If we measure for quadrupole
• either GR is wrong, i.e. No-Hair theorem
  violated!
• or we have discovered a new kind of object, e.g.
  a quark star

GR is wrong or Censorship Conjecture violated!
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Galactic Census with the SKA

• Blind survey for pulsars will discover
  10,000-20,000, practically complete census!
• Find all observable PSR-BH systems!
• High-Precision timing of discovered binary and
  millisecond pulsars

• Find them!
• Time them!
• VLBI them!

• Benefiting from SKA twice
• Unique sensitivity many pulsars, 10,000-20,000
  
• incl. many rare systems!
• Unique timing precision and multiple beams!

Not just a continuation of what has been done
before - Complete new quality of
science possible!
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Pulsar Astrophysics with SKA
Wide range of applications

• Galactic probes Interstellar medium/magnetic
  field
• Star formation history
• Dynamics
• Population via distances
  (ISM, VLBI)

Galactic Centre
Movement in potential
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Pulsar Astrophysics with SKA
Wide range of applications

• Galactic probes
• Extragalactic pulsars Missing Baryon Problem
  Formation Population
• Turbulent magnetized
  IGM

Search nearby galaxies!
Reach the local group!
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Pulsar Astrophysics with SKA
Wide range of applications

• Galactic probes
• Extragalactic pulsars
• Relativistic plasma physics Emission Processes
• Pulsar Wind
  Nebulae
• Magnetospheric
  Structure

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Pulsar Astrophysics with SKA
Wide range of applications

• Galactic probes
• Extragalactic pulsars
• Relativistic plasma physics
• Extreme Matter Physics Ultra-strong B-fields
• Equation-of-State
• Physics of Core
  collapse

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Pulsar Astrophysics with SKA
Wide range of applications

• Galactic probes
• Extragalactic pulsars
• Relativistic plasma physics
• Extreme Dense Matter Physics
• Multi-wavelength studies Photonic windows
• Non-photonic
  windows

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Pulsar Astrophysics with SKA
Wide range of applications
Holy Grail PSR-BH

• Galactic probes
• Extragalactic pulsars
• Relativistic plasma physics
• Extreme Dense Matter Physics
• Multi-wavelength studies
• Exotic systems planets
  pulsar/MS binaries
• millisecond pulsars
• relativistic binaries
• double pulsars
• PSR-BH systems

Double Pulsars
Planets
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Cosmological Gravitational Wave Background

• stochastic gravitational wave backgroundexpected
  on theoretical grounds

and also merging massive BH binaries
in early galaxy evolution
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Cosmological Gravitational Wave Background

• Pulsars discovered in Galactic Census also
• provide network of arms of a huge
• cosmic gravitational wave detector

PTA
Pulsar Timing Array

• Perturbation in
• space-time can be
• detected in timing
• residuals

• Sensitivity dimensionless strain

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Cosmological Gravitational Wave Background
Further by correlation
Improvement 104!
Spectral range nHz only accessible with SKA!
complementary to LISA, LIGO CMB
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Technical Requirements for Probing Fundamental
Physics with the SKA

• Blind Searching
• Periodicity searches
• Giant-pulse searches
• Pulse timing of discovered pulsars
• Astrometry using VLB baselines
• Other
• scintillation studies
• single pulse polarimetry
• synoptic studies (eclipsing systems,
  magnetospheric physics, etc)

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Blind Searching

• Traditional periodic dispersed pulses and single
  dispersed pulses
• Extension signals with greater time-frequency
  complexity than known pulsar signals (flare
  stars, GRBs, SETI, )
• Search as large a field of view as possible to
  maximize throughput and to allow multiple passes
  for transient objects
• Search domains
• Galactic plane (e.g. b lt 5)
• Galactic halo MSPs and binary pulsars
• Galactic center star cluster
• Nearby galaxies (periodic and single-pulse
  searches)
• Virgo cluster galaxies (giant pulse searches)

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Blind Searching for Pulsars

• Implications for SKA requirements
• Frequency range
• Antenna configuration
• Antenna connectivity and signal transport
• Real-time signal processing
• Quasi-real-time and long-term data management

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Blind Searching for Pulsars

• Implications for SKA requirements
• Frequency range
• 0.3 to 2 GHz for most Galactic and extragalactic
  directions
• gt 12 GHz for the Galactic center
• Antenna configuration
• compact core with significant fraction of the
  collecting area
• Antenna connectivity and signal transport
• Beamforming/correlation of all directly-connected
  antennas with 64 ?s dump times and 1024
  spectral channels across 20 bandwidth
• Real-time signal processing
• RFI excision
• Portion of pulsar search algorithm on data stream
  from each pixel
• Quasi-real-time and long-term data management
• Remainder of pulsar search algorithm
• Crosschecks between beams, etc. to further
  discriminate RFI and celestial signals
• Archival of low-and-high-level data products

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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
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Blind Searching Field of View

• To search ? deg2 with tbeam hr/beam requires
• T 104 hr tbeam/ 1 hr ?/104 deg2 / FOV/1
  deg2
• Sensitivity 35 times upcoming Arecibo ALFA
  surveys
• if full SKA sensitivity is available for
  searching (it wont)
• Need to maximize the searchable FOV and
  collecting area for blind searching
• Need a compact core with as much collecting area
  as possible (fcfraction in core) involving
  direct correlation of antennas (no stations)

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Primary beam synthesized beams
Blind surveys require full FOV sampling
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Blind Surveys with SKA
(pulsars, transients, ETI)

• Number of pixels needed to cover FOV
  Npix(bmax/D)2 104-109
• Number of operations Nops petaops/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

104 beams needed for full-FOV sampling
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SKA pulsar survey
64 ?s samples 1024 channels 600 s per beam 104
psrs
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Pulse Timing

• Can never have too much timing precision!
• ?TOA ? 100 ns is desirable
• Radiometer noise ?TOA ? W ? SEFD
• Systematics
• Pulse phase jitter ?TOA ? fjW(P/T)1/2
• Scattering-induced errors DM variations,
  variable pulse broadening ?TOA(DM) ? ?-2,
  ?TOA(PB) ??-4
• Pulse polarization calibration errors ? pulse
  shape changes ? TOA errors
• Need Stokes total I precision ? 1 or voltage
  polarization purity to better than 10-4 (-40 dB)

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Pulse Timing

• Multiple beaming and multiple FOV
• Follow up timing required to varying degrees on
  the 2x104 pulsars discoverable with SKA
• Spin parameters, DM and initial astrometry
• Orbital evolution for relativistic binaries
• Gravitational wave detection using MSPs
• Each deg2 will contain only a few pulsars
• ? efficient timing requires large solid-angle
  coverage (lower frequencies, subarrays, wide
  intrinsic FOV, or multiple FOVs)

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The need for multiplexed timing
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VLB Astrometry

• 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

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SKA Specifications Summary for Fundamental
Physics from Pulsars
Required Specification Required Specification Required Specification Required Specification Required Specification Required Specification
Topic ?t (?s) A/T (m2/K) ?max (GHz) Configuration FOV Sampling Polarization
Searching 50 2x104 fc 2.5 15 (GC) Core with large fc full Total Intensity
Timing ? 1 2x104 15 Non-critical if phasable 100 beams/deg2 Full Stokes -40 dB isolation
Astrometry (VLB) 200 gt2x103 8 Intercontinental baselines 3 beams Total Intensity

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The road to the SKA

• ALFA
• Prototypes ATA, LAR, EMBRACE, SKAMP
• International SKA demonstrator

• Timing
• Arecibo-like precision
• Searching
• 2000-5000 pulsars

?
Is this all we need?
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Projected Discoveries
Today
Future
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Projected Discoveries
Millisecond Pulsars
Relativistic Binaries
Today
Today
Future
Future
only 6!
SKA
SKA
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Work with SKA prototypes

• Searches
• - Chances to find 200-400 MSPs
• - Location of demonstrators is important!!
• - For PSR-BH we need to look at GC Cluster
• but one may be lucky

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Work with SKA prototypes

• Searches
• - Chances to find 200-400 MSPs
• - Location of demonstrators is important!!
• - For PSR-BH we need to look at GC Cluster
• but one may be lucky
• Timing
• - Some improvement for GW-limit

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Gravitational Wave Background

• With SKA about
• 104 improvement

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Gravitational Wave Background

• With prototype we
• may detect massive
• BH binaries
• We will not set
• very stringent limit
• on strings etc.

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Work with SKA prototypes

• Searches
• - Chances to find 200-400 MSPs
• - Location of demonstrators is important!!
• - For PSR-BH we need to look at GC Cluster
• but one may be lucky
• Timing
• - Some improvement for GW-limit

45
Work with SKA prototypes

• Searches
• - Chances to find 200-400 MSPs
• - Location of demonstrators is important!!
• - For PSR-BH we need to look at GC Cluster
• but one may be lucky
• Timing
• - Some improvement for GW-limit
• - IF we found PSR/BH,
• extremely unlikely to measure BH spin
• - If measurement, about few ? 10

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Timing of PSR/BH
SKA Demonstrator
d2x/dt2
dx/dt
sin(i)
?
Fractional Error
dPb/dt
?
Timing precision of essential Post-Keplerian
parms.
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Timing of PSR/BH
SKA
SKA Demonstrator
d2x/dt2
dx/dt
sin(i)
?
Fractional Error
Fractional Error
dPb/dt
?
Timing precision of essential Post-Keplerian
parms.
48
Work with SKA prototypes

• Searches
• - Chances to find 200-400 MSPs
• - Location of demonstrators is important!!
• - For PSR-BH we need to look at GC Cluster
• but one may be lucky
• Timing
• - Some improvement for GW-limit
• - IF we found PSR/BH,
• extremely unlikely to measure BH spin
• - If measurement, about few ? 10
• - Impossible to measure BH quadrupole moment

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Timing of PSR/BH

• Need to detect transient signals with amplitude
  of 10ns-1?s
• Periodically occurring at periastron
• Need instantaneous sensitivity to resolve it

Wex Kopeikin (1999)

• We can average data of different orbits e.g.
  for 30 ns signal
• we need to average about 1000 TOAs (per orb.
  phase)
• ? with only 2 TOAs per day, SKA needs less than
  1.5 years
• With SKA demonstrator, we need 14 years

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Work with SKA prototypes

• Searches
• - Chances to find 200-400 MSPs
• - Location of demonstrators is important!!
• - For PSR-BH we need to look at GC Cluster
• but one may be lucky
• Timing
• - Some improvement for GW-limit
• - IF we found PSR/BH,
• extremely unlikely to measure BH spin
• - If measurement, about few ? 10
• - Impossible to measure BH quadrupole moment

Demonstrator is not good enough!
We need the REAL SKA!
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The SKA Pulsar Sky
? Was Einstein right? Fundamental question in
physics quest for
quantum gravity! ? Unique to radio astronomy -
Only possible with the SKA! ? It excites public
and community e.g. Quarks Cosmos
gt1 Million
websites
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Pulsar Science

• Extreme matter physics
• 10x nuclear density
• High-temperature superfluid superconductor
• B Bq 4.4 x 1013 Gauss
• Voltage drops 1012 volts
• FEM 109Fg 109 x 1011FgEarth
• Relativistic plasma physics (magnetospheres)
• Tests of theories of gravity
• Gravitational wave detectors
• Probes of turbulent and magnetized ISM ( IGM)
• End states of stellar evolution

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Why more pulsars?

• Discover rare, extreme objects (odds ? Npsr)
• P lt 1 ms P gt 8 sec
• Porb lt hours B gtgt 1013 G (link to
  magnetars?)
• V gt 1000 km s-1 strange stars?
• NS-NS and NS-BH binaries, planets
• Extragalactic pulsars
• Galactic center pulsars orbiting Sgr A black
  hole

Large N ? Galactic tomography

• Large Npsr ? Galactic tomography of B ?B, ne
  ?ne
• Branching ratios for compact
  object formation
• NS (normal, isolated)
• NS (recycled, binaries)
• NS (magnetar)
• BH (hypernovae)
• Strange stars?

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How to do it?

• Find them
• Time them
• VLBI them

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Summary on Pulsar Searching

• SKA can perform a Galactic census of neutron
  stars that will surpass previous surveys by a
  factor gt 10.
• The discovery space includes exotic objects that
  provide opportunities for testing fundamental
  physics.
• Pulsar searches place particular demands on the
  ability to do full FOV sampling at high time
  resolution (64 ?s) with 1024 channels over gt 400
  MHz at 1-2 GHz.
• High frequencies (gt 10 GHz) are needed for
  Galactic center searches to combat scattering.
• Further simulations are needed that use detailed
  information from existing pulsar surveys and
  particular SKA configurations.

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Some comments about multiple FOV

• FOV defined to be the 1 deg2 FOV specn
• Multiple FOV means NFOV x (1 deg2)
• How to achieve NFOV ?
• Tiles FWHM gtgt 1 deg2
• OK for targeted observations
• Blind surveys same pixelization requirement as
  other concepts Npixels (bmax/D)2 gtgtgt 102
• LNSD subarrays ? trade Aeff/Tsys

57
Was Einstein right?
Compact PSR binaries
We will probe BH properties with pulsars and
SKA - precise measurements - no
assumptions about EoS or accretion physics -
test masses well separated, not deformed
58
Black Hole properties
spin and quadrupole moment

• Astrophysical black holes are expected to rotate

S angular momentum

• Result is relativistic spin-orbit coupling
• Visible as a precession of the orbit
• Measure higher order derivatives of secular
• changes in semi-major axis and longitude of
• periastron
• Not easy! It is not possible today!
• Requires SKA sensitivity!

See Wex Kopeikin (1999)
59
Black Hole properties
Black Hole quadrupole moment

• Spinning black holes are oblate

Q quadrupole moment
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Summary
Pulsars discovered and observed with the SKA

• unprecedented sensitivity
  revolution in pulsar physics
• probe wide range of physical problems
• tackle unanswered fundamental questions

• Was Einstein right?
• What are Black Hole properties?
• What physics describe spinning dipoles?
• What is EOS of dense matter?
• What happens in supracritical B field?
• Is there a Cosmological gravitational wave
  background?

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