Pulsar Science with the SKA:

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Pulsar Science with the SKA
Strong Field Tests Of Gravity Using Pulsars
Black Holes

• Michael Kramer
• Jim Cordes
• Leiden SKA Science Retreat

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Pulsars

• almost Black Holes
• objects of extreme matter
• 10x nuclear density
• B Bq 4.4 x 1013 Gauss
• Voltage drops 1012 volts
• FEM 109Fg 1011FgEarth
• High-temperature superfluid superconductor
• relativistic plasma physics in action
• probes of turbulent and magnetized ISM
• precision tools, e.g.
• - Period of B193721 P
  0.0015578064924327?0.0000000000000004 s
• - Orbital eccentricity of J10125307
  elt0.0000008
• testing ground for theories of gravity
• cosmological gravitational wave detectors

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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 Conversation Laws etc.

Solar System tests provide constraints
but only in weak field!
No test of any other 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 Conversation Laws etc.

Example Scalar-Tensor theory passing all solar
system tests
Fails Binary Pulsars!
Damour Esposito-Farese (1996)
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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 Conversation Laws etc.

Binary Pulsars

• Clean strong-field tests, incl.
• Gravitational Radiation (dipole higher orders)
• Geodetic Precession

So far General Relativity has passed all tests
with flying colours!
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Was Einstein right?
General Relativity vs Alternative Theories

• Ultra-strong limit?
• Description of stellar super-massive Black
  Holes?
• Gravitational Wave Background?

Only SKA can provide the answer to all these
questions!
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Galactic Census

• Blind survey for pulsars
• Time discovered binary and millisecond pulsars
• to very high precision

• 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!

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Pulsar Science with the SKA
Very 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 Science with the SKA
Very wide range of applications

• Galactic probes
• Extragalactic pulsars Formation Population
• Turbulent magnetized
  IGM

Search nearby galaxies!
Reach the local group!
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Pulsar Science with the SKA
Very wide range of applications

• Galactic probes
• Extragalactic pulsars
• Relativistic plasma physics Radio emission
• Resolving
  magnetospheres
• Relation to
  high-energies

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Pulsar Science with the SKA
Very wide range of applications

• Galactic probes
• Extragalactic pulsars
• Relativistic plasma physics
• Extreme Dense Matter Physics Ultra-strong
  B-fields
• 
  Equations-of-State
• Core
  collapses

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Pulsar Science with the SKA
Very wide range of applications

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

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Pulsar Science with the SKA
Very 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 Science with the SKA
Very wide range of applications

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

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Pulsar Science with the SKA
Very wide range of applications

• Galactic probes
• Extragalactic pulsars
• Relativistic plasma physics
• Extreme Dense Matter Physics
• Multi-wavelength studies
• Exotic systems
• Gravitational physics ultra-strong gravity
• black hole properties
  (stellar
• supermassive BH in
  the GC)
• cosmological
  gravitational wave
• background

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Pulsar Science with the SKA
"For free!"
Very wide range of applications

• Galactic probes
• Extragalactic pulsars
• Relativistic plasma physics
• Extreme Dense Matter Physics
• Multi-wavelength studies
• Exotic systems
• Gravitational physics ultra-strong gravity
• black hole properties
  (stellar
• supermassive BH in
  the GC)
• cosmological
  gravitational wave
• background

Level-0 Proposal
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Level-0 Strong gravity with PSRs NHs
Science Ultra-strong field tests

• Use tight binary systems, e.g. close to
  coalescence
• Could be both NS-NS and NS-BH systems
• Measure theory-independent relativistic
  corrections
• Compare their description
• in competing theories

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Level-0 Strong gravity with PSRs NHs
Science Ultra-strong field tests

• Use tight binary systems, e.g. close to
  coalescence
• Could be both NS-NS and NS-BH systems
• Measure theory-independent relativistic
  corrections
• Compare their description
• in competing theories

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Level-0 Strong gravity with PSRs NHs
Science Ultra-strong field tests

• Use tight binary systems, e.g. close to
  coalescence
• Could be both NS-NS and NS-BH systems
• Measure theory-independent relativistic
  corrections
• Compare their description
• in competing theories

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Level-0 Strong gravity with PSRs NHs
Science Black hole properties

• Goal Millisecond pulsar around BH
• Real black holes should rotate try to measure
  spin!

S angular momentum, for Kerr BH ??1 in GR
? gt 1 ? naked singularity!
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Level-0 Strong gravity with PSRs NHs
Science Black hole properties

• Measure spin and quadrupole moment via orbital
• precession to test BH description in GR!

Wex Kopeikin (1999)

• Not easy! Requires SKA sensitivity!!
• Even easier for (super-) massive black holes!

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Level-0 Strong gravity with PSRs NHs
Science Black hole properties
Finally, we point out that the discovery of a
binary pulsar with a black-hole companion has
the potential of providing a superb new probe of
relativistic gravity. The discriminating power
of this probe might supersede all its present
and foreseeable competitors Damour
Esposito-Farese (1998)
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Level-0 Strong gravity with PSRs NHs
Science Cosmological Gravitational Wave
Background

• Two categories of sources producing stochastic
• background
• - inflation evolution of extra dimensions or
• decay of cosmic strings (see
  GUTs)
• - coalescence of massive Black Holes during
• galaxy evolution

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Level-0 Strong gravity with PSRs NHs
Science Cosmological Gravitational Wave
Background

• Two categories of sources producing stochastic
• background
• - inflation evolution of extra dimensions or
• decay of cosmic strings (see
  GUTs)
• - coalescence of massive Black Holes during
• galaxy evolution
• Three ways of probing them
• - polarization of CMB very low frequencies
• - LIGO/LISA high frequencies
• - Pulsar Timing Array nHz, only accessible
  to SKA

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Level-0 Strong gravity with PSRs NHs
Science Cosmological Gravitational Wave
Background

• Millisecond pulsars act as arms of huge detector

Pulsar Timing Array Look for global spatial
pattern in timing residuals!

• Complementary in Frequency!

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Level-0 Strong gravity with PSRs NHs

• Was Einstein right?
• What are the Black Hole properties?
• What is the nature of a cosmological
  gravitational
• wave background if it exists?

• All are fundamental questions in physics yet
  unanswered!
• Their answer using radio pulsars is unique to
  SKA!
• Pulsars also visible in every astronomical
  window
• but only radio allows their timing with high
  precision
• study providing key observations for other
  wavelengths
• Pulsars, Gravity and in particular Black Holes
• fascinate not only funding agencies but also
  public!

All criteria met!!
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Technical Requirements
Primary beam synthesized beams
Full FOV sampling
Blind Surveys
Targeted observations e.g.timing
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Blind Surveys with SKA

• Need to fill the whole FOV
• Number of pixels needed Npix(bmax/D)2 104
• Number of operations
• Nops petaops/s
• Post processing per beam
• e.g. standard pulsar periodicity
• analysis
• Requires signal transport of
• individual antennas to correlator
• Correlator speed depends strongly on number of
• antennas that are directly connected to
  correlator

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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

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Precision Pulsar Timing
Consider

• Fast(!) sampling
• High sensitivity
• Systematics, e.g. solar system ephemeredes,
• time standards WORK TO
  DO!
• Astrometry (VLBI) to correct for kinematics
• Interstellar weather
• Multipath scattering
• Timing noise, Profile stability (?)

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Summary Pulsars with the SKA

• Overwhelming science case
• New quality due to both leap in numbers and
  timing precision
• Modest frequency coverage but large bandwidth
• Large number of simultaneous beams/FOVs
  desirable
• Detailed requirements different for searching
  timing
• - both modes are necessary to obtain science!!
• Frequency coverage up to 15 GHz
• A/T 20,000 m2/K from 500 MHz to 5000 MHz
• FOV 1 deg2 or larger(!)
• Configuration 80 within 1 km, 20 at VLBI
  scales
• Significant post-processing requirements
• 50 ?s sampling full FOV for searching
• lt1?s sampling for pencil beam

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Multiple FOVs Initial Simulation Results
Simulated Population
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Multiple FOVs Initial Simulation Results
Simulated Population
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Multiple FOVs Initial Simulation Results
Simulated Population
Required time for one(!) timing point
All Pulsars
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Multiple FOVs Initial Simulation Results
Simulated Population
Required time for one(!) timing point
Millisecond Pulsars