Fundamental Physics and Astrophysics using Pulsars and the SKA Jim Cordes Cornell U. Vicky Kaspi McGill U. Michael Kramer 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 > B q = 4.4 x G –Voltage drops ~ volts –F EM = 10 9 F g = F gEarth –Tsurf ~ million K …relativistic plasma physics in action …probes of turbulent and magnetized ISM …precision tools, e.g. - Period of B : P =  s - Orbital eccentricity of J : e<

Noted GR Laboratories Weisberg & Taylor (priv. comm) Orbit shrinks every day by 1cm Confirmation of existence of gravitational waves Hulse & Taylor (1974)

First Double Pulsar! P b =2.4 hrs, d  /dt=17 deg/yr M A =1.337(5)M , M B =1.250(5)M  Lyne et al.(2004) Testing GR: 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. 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! 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!

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!

Exploration of Black Holes We will probe BH properties with pulsars and SKA: - precise measurements - no assumptions about EoS or accretion physics - test masses well separated, not deformed Compact PSR Binaries

spin and quadrupole moment: Black Hole properties 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!

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!

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” theorem violated! or we have discovered a new kind of object, e.g. a quark star GR is wrong or Censorship Conjecture violated!

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!

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

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

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:

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 Pulsar Astrophysics with SKA Wide range of applications: Holy Grail: PSR-BH Double Pulsars Planets

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

Cosmological Gravitational Wave Background Pulsars discovered in Galactic Census also provide network of arms of a huge cosmic gravitational wave detector Perturbation in space-time can be detected in timing residuals Sensitivity: dimensionless strain Pulsar Timing Array PTA:

Cosmological Gravitational Wave Background LISA Pulsars Advanced LIGO Spectral range: nHz only accessible with SKA! Further by correlation: PTA limit: Improvement: 10 4 ! CMB complementary to LISA, LIGO & CMB

Technical Requirements for Probing Fundamental Physics with the SKA Blind SearchingBlind Searching –Periodicity searches –Giant-pulse searches Pulse timing of discovered pulsarsPulse timing of discovered pulsars Astrometry using VLB baselinesAstrometry using VLB baselines OtherOther: 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 2 with t beam hr/beam requires: T = 10 4 hr [t beam / 1 hr] [  /10 4 deg 2 ] / [FOV/1 deg 2 ]  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 (f c =fraction in core) involving direct correlation of antennas (no stations)

Primary beam & synthesized beams Blind surveys require full FOV sampling

Blind Surveys with SKA Number of pixels needed to cover FOV: N pix ~(b max /D) 2 ~ Number of operations N ops ~ 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 (pulsars, transients, ETI) ≥10 4 beams needed ≥10 4 beams needed for full-FOV sampling

64  s samples 1024 channels 600 s per beam ~10 4 psr’s SKA pulsar survey

Pulse Timing Can never have too much timing precision!  TOA  100 ns is desirable Radiometer noise:  TOA  W  SEFD Systematics: Pulse phase jitter:  TOA  f j W(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 (-40 dB)

Pulse Timing Multiple beaming and multiple FOV: –Follow up timing required to varying degrees on the ~ 2x10 4 pulsars discoverable with SKA Spin parameters, DM and initial astrometry Orbital evolution for relativistic binaries Gravitational wave detection using MSPs –Each deg 2 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 Topic  t (  s) A/T (m 2 /K) max (GHz) Configuration FOV Sampling Polarization Searching 502x10 4 f c (GC) Core with large f c full Total Intensity Timing  12x Non-critical if phasable 100 beams/deg 2 Full Stokes; -40 dB isolation Astrometry (VLB) 200>2x Intercontinental baselines ~ 3 beams Total Intensity

The road to the SKA: Parkes Multibeam High-frequency surveys ALFA SKA ALFA Prototypes: ATA, LAR, EMBRACE, SKAMP International SKA demonstrator Timing: Arecibo-like precision Searching: pulsars Is this all we need? ?

Projected Discoveries TodayFuture

Projected Discoveries Today Future SKA only 6! Millisecond PulsarsRelativistic Binaries

Work with SKA prototypes Searches: - Chances to find ~ 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 ~ 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 10 4 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 ~ 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 ~ 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 Timing precision of essential Post-Keplerian parms. dP b /dt ώ γ sin(i) dx/dt d 2 x/dt 2 Fractional Error

Timing of PSR/BH SKA Demonstrator SKA Timing precision of essential Post-Keplerian parms. dP b /dt ώ γ sin(i) dx/dt d 2 x/dt 2 Fractional Error

Work with SKA prototypes Searches: - Chances to find ~ 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 Wex & Kopeikin (1999): Need to detect transient signals with amplitude of ~10ns-1  s Periodically occurring at periastron Need instantaneous sensitivity to resolve it 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 ~ 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 We need the REAL SKA! Demonstrator is not good enough!

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

Pulsar Science Extreme matter physics –10x nuclear density –High-temperature superfluid & superconductor –B ~ B q = 4.4 x Gauss –Voltage drops ~ volts –F EM = 10 9 F g = 10 9 x F gEarth Relativistic plasma physics (magnetospheres) Tests of theories of gravity Gravitational wave detectors Probes of turbulent and magnetized ISM (& IGM) End states of stellar evolution

Why more pulsars? Discover rare, extreme objects (odds  N psr ) P 8 sec P orb > G (link to magnetars?) V > 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 psr  Galactic tomography of B +  B, n e +  n e Branching ratios for compact object formation: NS (normal, isolated) NS (recycled, binaries) NS (magnetar) BH (hypernovae) Strange stars? Large N  Galactic tomography

How to do it? Find them Time them VLBI them

Summary on Pulsar Searching SKA can perform a Galactic census of neutron stars that will surpass previous surveys by a factor > 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 > 400 MHz at 1-2 GHz. High frequencies (> 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.

Some comments about multiple FOV FOV defined to be the 1 deg 2 FOV spec’n Multiple FOV means N FOV x (1 deg 2 ) How to achieve N FOV ? Tiles: FWHM >> 1 deg 2 OK for targeted observations Blind surveys: same pixelization requirement as other concepts: N pixels = (b max /D) 2 >>> 10 2 LNSD: subarrays  trade A eff /T sys

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

spin and quadrupole moment: Black Hole properties 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)

Black Hole quadrupole moment: Black Hole properties Spinning black holes are oblate Q = quadrupole moment Result is classical spin-orbit coupling Visible as transient signals in timing residuals Even more difficult! Requires SKA! Wex & Kopeikin (1999):

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? Summary Pulsars discovered and observed with the SKA… unprecedented sensitivity: revolution in pulsar physics probe wide range of physical problems tackle unanswered fundamental questions: