Pulsar Science with the SKA by yG72wS5

VIEWS: 5 PAGES: 51

									                  Fundamental
                    Physics
                       and
                  Astrophysics
                      using
              Pulsars and the SKA


Jim Cordes       Vicky Kaspi   Michael Kramer
 Cornell U.       McGill U.    Jodrell Bank
      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
                   Pulsars…
• embody physics of the EXTREME
   – surface speed ~0.1c
   – 10x nuclear density in centre
   – some have B > 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 B1937+21:
        P = 0.00155780649243270.0000000000000004 s
     - Orbital eccentricity of J1012+5307: e<0.0000008
                         Noted GR Laboratories

 Hulse & Taylor (1974)              Weisberg & Taylor (priv. comm)




• Orbit shrinks every day by 1cm
• Confirmation of existence of gravitational waves
                    First Double Pulsar!




Lyne et al.(2004)


• Pb=2.4 hrs, d/dt=17 deg/yr    Testing GR:
• MA=1.337(5)M, MB=1.250(5)M
                                 s obs
                                   exp
                                        1.000  0.002
                                 s         Kramer et al.(2004)
                          Was Einstein right?
   General Relativity                      vs       Alternative Theories
                            • Strong Equivalence Principle
                            • Violation of Lorentz-Invariance
                            • Violation of Positional Invariance
                            • Violation of Conservation Laws etc.
       Albert Einstein




               Solar System tests provide constraints
                              …but only in weak field!                   v
                                                                                    10  4
                                                                          c  orbit
v                      No test of any theory of gravity is
           10 3                                                       Sun  10 6
 c  orbit              complete, if only done in solar system,
 PSR  0.15             i.e. strong field limit and radiative aspects    Earth  10 10
 BH  0.5               need to be tested, too!                          Moon  10 11

   This is and will be done best with radio pulsars!
                    Was Einstein right?
General Relativity                vs      Alternative Theories
                    • Strong Equivalence Principle
                    • Violation of Lorentz-Invariance
                    • Violation of Positional Invariance
                    • Violation of Conservation Laws etc.
  Albert Einstein




Binary Pulsars: • Clean strong-field tests, incl.
                          • Shapiro delays
                          • Gravitational Radiation
                          • Geodetic Precession
                     So far:
                     General Relativity has passed
                     all tests with flying colours!
     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
           Black Hole properties
spin and quadrupole moment:

•Astrophysical black holes are expected to rotate
                           4         S = angular momentum
    c S               c Q
      2           q 2 3           Q = quadrupole moment

    GM                G M
• 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!
      Cosmic Censorship & No-Hair
• For BH-like companions to pulsars, we will
measure spin precisely
• In GR, for Kerr-BH we expect:      1
But if we measure
            > 1  Event Horizon vanishes
                  Naked singularity!
  GR is wrong or Censorship Conjecture violated!
      Cosmic Censorship & No-Hair
• For BH-like companions to pulsars, we will
measure spin precisely
• In GR, for Kerr-BH we expect:      1
But if we measure
            > 1  Event Horizon vanishes
                  Naked singularity!
  GR is wrong or Censorship Conjecture violated!

If we measure for quadrupole     q      2


either GR is wrong, i.e. “No-Hair” theorem violated!
or we have discovered a new kind of object,
e.g. a quark star
          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 been done before
  Not just a continuation of what hassystems!
              - Complete new quality beams!
• Unique timing precision and multiple of science possible!
        Pulsar Astrophysics with SKA
Wide range of applications:
  • Galactic probes: Interstellar medium/magnetic field
 Magnetic field      Star formation history
                     Dynamics
                     Population via distances (ISM, VLBI)
                                    Electron
                                  distribution




 Movement in potential                  Galactic Centre
        Pulsar Astrophysics with SKA
Wide range of applications:
   • Galactic probes
   • Extragalactic pulsars: Missing Baryon Problem
                            Formation & Population
                            Turbulent magnetized IGM
                              Giant pulses
 Search nearby galaxies!




                               Reach the local group!
         Pulsar Astrophysics with SKA
Wide range of applications:
   • Galactic probes
   • Extragalactic pulsars
   • Relativistic plasma physics: Emission Processes
                                  Pulsar Wind Nebulae
                                  Magnetospheric Structure
            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
           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
           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
     Cosmological Gravitational Wave Background

   • stochastic gravitational wave background
   expected on theoretical grounds
Possible Sources:
          • Inflation
          • String cosmology
          • Cosmic strings
                                h GW ( f ) ~ const.
                                 2
                                 0

          • phase transitions


and also: merging massive BH binaries
                                        h02GW ( f )  f 2 / 3
          in early galaxy evolution
   Cosmological Gravitational Wave Background

• Pulsars discovered in Galactic Census also
  provide network of arms of a huge
  cosmic gravitational wave detector
                                       PTA:
• Perturbation in                          Pulsar
  space-time can be                          Timing
  detected in timing                            Array
  residuals

• Sensitivity: dimensionless strain
                                TOA
                  hc ( f ) ~
                                T
      Cosmological Gravitational Wave Background
                        Advanced
CMB       Pulsars   LISA LIGO

                                     PTA limit:
                                     h GW ( f ) ~ 
                                      2
                                      0
                                                       2
                                                       TOA   f   4


                                     Further by correlation:

                                          1 / N PSR


                                    Improvement: 104!

                                   Spectral range: nHz
                                   only accessible with SKA!
                                    complementary to
                                    LISA, LIGO & CMB
 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)
                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| < 5°)
   –   “Galactic halo” MSPs and binary pulsars
   –   Galactic center star cluster
   –   Nearby galaxies (periodic and single-pulse searches)
   –   Virgo cluster galaxies (giant pulse searches)
             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
               Blind Searching for
                     Pulsars
Implications for SKA requirements:
   – Frequency range
       • 0.3 to 2 GHz for most Galactic and extragalactic directions
       • > 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
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
   Blind Searching: Field of
             View
To search  deg with tbeam hr/beam requires:
           2


     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 won’t)

     Need to maximize the searchable FOV and collecting
      area for blind searching
      Need a compact core with as much collecting area as
      possible (fc=fraction in core) involving direct correlation
      of antennas (no stations)
 Primary beam &     Blind surveys require full
synthesized beams        FOV sampling
     Blind Surveys with SKA
                    (pulsars, transients, ETI)
• Number of pixels needed to                      ≥104 beams needed
  cover FOV:
      Npix~(bmax/D)2 ~104-109                    for full-FOV sampling
• 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
SKA pulsar survey


                    64 s samples
                    1024 channels


                    600 s per beam


                    ~104 psr’s
                  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)
              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)
The need for multiplexed timing:
          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
            SKA Specifications Summary
            for Fundamental Physics
            from Pulsars
                               Required Specification
              t      A/T         max                           FOV
   Topic                                     Configuration                 Polarization
             (s)    (m2/K)      (GHz)                         Sampling

                                   2.5     Core with large                   Total
Searching    50     2x104 fc                                     full
                                 15 (GC)         fc                        Intensity
                                                                               Full
                                            Non-critical if      100         Stokes;
Timing       1     2x104          15
                                              phasable        beams/deg2     -40 dB
                                                                            isolation

Astrometry                                 Intercontinental                  Total
             200    >2x103         8                          ~ 3 beams
(VLB)                                         baselines                    Intensity
            The road to the SKA:
• ALFA
• Prototypes: ATA, LAR, EMBRACE, SKAMP
• International SKA demonstrator
                                    • Timing:
                                      Arecibo-like precision

           High-frequency surveys   • Searching:
                                      2000-5000 pulsars
   Parkes Multibeam
                          ALFA

                             ?
                                      Is this all we need?
                           SKA
Projected Discoveries
          Today Future
   Projected Discoveries
Millisecond Pulsars    Relativistic Binaries
       Today Future             Today Future




                          only 6!
                 SKA                      SKA
       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
       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
Gravitational Wave Background

                        •With SKA about
                         104 improvement
Gravitational Wave Background

                       •With prototype we
                        may detect massive
                        BH binaries
                       •We will not set
                        very stringent limit
                        on strings etc.
       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
        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%
                              Timing of PSR/BH
                   SKA Demonstrator
                                d2x/dt2

                                 dx/dt
Fractional Error




                                  sin(i)
                                      γ
                                dPb/dt


                                      ώ

Timing precision of essential Post-Keplerian parms.
                              Timing of PSR/BH
                   SKA Demonstrator                           SKA
                                d2x/dt2

                                 dx/dt
Fractional Error




                                           Fractional Error
                                  sin(i)
                                      γ
                                dPb/dt


                                      ώ

Timing precision of essential Post-Keplerian parms.
       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
                   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
       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!
               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” &
                                         >1 Million websites

								
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