Fundamental Physics and Astrophysics using Pulsars and the SKA

1. Fundamental Physics andAstrophysicsusingPulsars and the SKA Jim Cordes Cornell U. Vicky Kaspi McGill U. Michael Kramer Jodrell Bank

2. 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

3. 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

4. Noted GR Laboratories Weisberg & Taylor (priv. comm) Hulse & Taylor (1974) • Orbit shrinks every day by 1cm • Confirmation ofexistence ofgravitational waves

5. Testing GR: Kramer et al.(2004) First Double Pulsar! Lyne et al.(2004) • Pb=2.4 hrs, d/dt=17 deg/yr • MA=1.337(5)M, MB=1.250(5)M

6. 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!

7. 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!

8. 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

9. 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!

10. 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 •  > 1  Event Horizon vanishes •  Naked singularity! GR is wrong or Censorship Conjecture violated!

11. 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 •  > 1  Event Horizon vanishes •  Naked singularity! • If we measure for quadrupole • either GR is wrong, i.e. “No-Hair” theoremviolated! • or we have discovered a new kind of object, e.g. a quark star GR is wrong or Censorship Conjecture violated!

12. 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!

13. Electron distribution Magnetic field Pulsar Astrophysics with SKA Wide range of applications: • Galactic probes:Interstellar medium/magnetic field • Star formation history • Dynamics • Population via distances (ISM, VLBI) Movement in potential Galactic Centre

14. Giant pulses Pulsar Astrophysics with SKA Wide range of applications: • Galactic probes • Extragalactic pulsars:Missing Baryon ProblemFormation & Population • Turbulent magnetized IGM Search nearby galaxies! Reach the local group!

15. Pulsar Astrophysics with SKA Wide range of applications: • Galactic probes • Extragalactic pulsars • Relativistic plasma physics:Emission Processes • Pulsar Wind Nebulae • Magnetospheric Structure

16. 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

17. 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

18. 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

19. Possible Sources: • Inflation • String cosmology • Cosmic strings • phase transitions Cosmological Gravitational Wave Background • stochastic gravitational wave backgroundexpected on theoretical grounds and also: merging massive BH binaries in early galaxy evolution

20. 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

21. Advanced LIGO Pulsars LISA CMB PTA limit: Cosmological Gravitational Wave Background Further by correlation: Improvement: 104! Spectral range: nHz only accessible with SKA! complementary to LISA, LIGO & CMB

22. 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)

23. 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)

24. 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

25. 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

26. 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

27. Blind Searching: Field of View To search  deg2 with tbeam hr/beam requires: T = 104 hr [tbeam/ 1 hr] [/104 deg2] / [FOV/1deg2] • 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)

28. Primary beam & synthesized beams Blind surveys require full FOV sampling

29. Blind Surveys with SKA • (pulsars, transients, ETI) ≥104 beams needed for full-FOV sampling • 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

31. SKA pulsar survey 64 s samples 1024 channels 600 s per beam ~104 psr’s

32. 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)

33. 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)

34. The need for multiplexed timing:

35. 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

36. SKA Specifications Summary for Fundamental Physics from Pulsars

37. High-frequency surveys Parkes Multibeam ALFA SKA 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?

38. Projected Discoveries Today Future

39. Projected Discoveries Millisecond Pulsars Relativistic Binaries Today Future Today Future only 6! SKA SKA

40. 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

41. 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 improvementfor GW-limit

42. Gravitational Wave Background • With SKA about • 104 improvement

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

44. 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 improvementfor 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 improvementfor GW-limit • - IF we found PSR/BH, • extremely unlikely to measure BH spin • - If measurement, about few  10%

46. Timing of PSR/BH SKA Demonstrator d2x/dt2 dx/dt sin(i) γ Fractional Error dPb/dt ώ Timing precision of essential Post-Keplerian parms.

47. Timing of PSR/BH SKA SKA Demonstrator d2x/dt2 dx/dt sin(i) γ Fractional Error Fractional Error dPb/dt ώ 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 improvementfor GW-limit • - IF we found PSR/BH, • extremely unlikely to measure BH spin • - If measurement, about few  10% • -Impossible to measure BH quadrupole moment

49. 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

50. 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 improvementfor 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!