Fundamental Physics and Astrophysics using Pulsars and the SKA Jim Cordes Cornell U. Vicky Kaspi McGill U. Michael Kramer Jodrell Bank

Fundamental Fundamental Physics Physics

andandAstrophysicsAstrophysics

usingusingPulsars and the SKAPulsars and the SKA

Jim Cordes Cornell U.

Vicky Kaspi McGill U.

Michael Kramer Jodrell Bank

Pulsar Science Pulsar Science HighlightsHighlights

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…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 = 0.00155780649243270.0000000000000004

s - Orbital eccentricity of J1012+5307: e<0.0000008

Noted GR LaboratoriesNoted GR Laboratories

Weisberg & Taylor (priv. comm)

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

Hulse & Taylor (1974)

First Double Pulsar!First Double Pulsar!

• Pb=2.4 hrs, d/dt=17 deg/yr

• MA=1.337(5)M, MB=1.250(5)M

Lyne et al.(2004)

002.0000.1exp

obs

s

sTesting GR:

Kramer et al.(2004)

Was Einstein right?Was Einstein right?General Relativity vs Alternative Theories

Albert Einstein

• 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!

11

10

6

4

10

10

10

10

Moon

Earth

Sun

orbitc

v

No test of any theory of gravity iscomplete, 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 iscomplete, if only done in solar system, i.e. strong field limit and radiative aspects need to be tested, too!

5.0

15.0

10 3

BH

PSR

orbitc

v

This is and will be done best with radio This is and will be done best with radio pulsars! pulsars!

Was Einstein right?Was Einstein right?General Relativity vs Alternative Theories

Albert Einstein

• 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 PrecessionSo far:

General Relativity has passed all tests with flying colours!

Exploration of Black HolesExploration 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 propertiesBlack Hole properties

•Astrophysical black holes are expected to rotate

2M

S

G

c

S = angular momentumQ = 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!

32

4

M

Q

G

cq

Cosmic Censorship & No-Cosmic Censorship & No-HairHair

• 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-Cosmic Censorship & No-HairHair

• 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!

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!

2q

Galactic Census with the SKAGalactic 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 SKAPulsar Astrophysics with SKA Wide range of applications:

ElectronElectron

distributiondistribution

ElectronElectron

distributiondistribution

Magnetic fieldMagnetic field

Galactic CentreMovement in potential

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


Giant pulsesGiant pulses

Reach the local group!

Search nearby galaxies!

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


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


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


• 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


Holy Grail: PSR-BH

Double PulsarsPlanets

Cosmological Gravitational Wave Cosmological Gravitational Wave BackgroundBackground

• stochastic gravitational wave backgroundexpected on theoretical grounds

and also: merging massive BH binaries in early galaxy evolution

Possible Sources:

• Inflation• String cosmology• Cosmic strings• phase transitions

.~)(20 constfh GW

3/220 )( ffh GW


• 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

Tfh TOA

c

~)(

Pulsar Timing Array

PTA:


LISAPulsarsAdvanced

LIGO

Spectral range: nHzonly accessible with SKA!

Further by correlation:

PSRN/1

PTA limit:422

0 ~)( ffh TOAGW

Improvement: 104!

CMB

complementary toLISA, LIGO & CMB

Technical Requirements for Probing Technical Requirements for Probing Fundamental Physics with the SKAFundamental Physics with the SKA

• Blind Searching Blind 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 SearchingBlind 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 Blind Searching for PulsarsPulsars

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 Blind Searching for PulsarsPulsars

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 Blind Searching: Field of ViewView

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 surveysif 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 & Primary beam & synthesized beamssynthesized beams

Blind surveys require full Blind surveys require full FOV samplingFOV sampling

Blind Surveys with SKABlind Surveys with SKA• Number of pixels needed to

cover FOV: Npix~(bmax/D)2 ~104-109

• Number of operationsNops~ 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)

≥≥10104 4 beams neededbeams needed

for full-FOV samplingfor full-FOV sampling

64 64 s sampless samples

1024 channels1024 channels

600 s per beam600 s per beam

~10~1044 psr’s psr’s

SKA pulsar survey

Pulse TimingPulse 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 TimingPulse TimingMultiple 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 The need for multiplexed timing:timing:

VLB AstrometryVLB 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 SKA Specifications Summary for Fundamental Summary for Fundamental Physics from PulsarsPhysics from Pulsars

Required SpecificationRequired Specification

TopicTopic t (s)

A/T (m2/K)

max

(GHz)Configuration

FOV Sampling

Polarization

Searching 50 2x104 fc

2.515 (GC)

Core with large fc

fullTotal

Intensity

Timing 1 2x104 15Non-critical if

phasable100

beams/deg2

Full Stokes;-40 dB

isolation

Astrometry (VLB)

200 >2x103 8Intercontinental

baselines~ 3

beamsTotal

Intensity

The road to the SKA: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: 2000-5000 pulsars

Is this all we need??

Projected DiscoveriesProjected Discoveries

Today Future

Projected DiscoveriesProjected Discoveries

Today TodayFuture Future

SKA SKAonly 6!

Millisecond Pulsars Relativistic Binaries

Work with SKA Work with SKA prototypesprototypes

• 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 Gravitational Wave Background

•With SKA about 104 improvement

Gravitational Wave Background Gravitational Wave Background

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



• Timing: - Some improvement for GW-limit



• 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 Timing of PSR/BH SKA Demonstrator

Timing precision of essential Post-Keplerian parms.

dPb/dt

ώ

γ

sin(i)

dx/dt

d2x/dt2

Fra

ctio

nal E

rror

Timing of PSR/BH Timing of PSR/BH SKA Demonstrator SKA

Timing precision of essential Post-Keplerian parms.

dPb/dt

ώ

γ

sin(i)

dx/dt

d2x/dt2

Fra

ctio

nal E

rror

Fra

ctio

nal E

rror



• 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/BHTiming of PSR/BH

We

x & K

op

eik

in

(199

9):

• Need to detect transient signals with amplitude of ~10ns-1s• 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



• 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 SkyThe 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

Documents

Fundamental Physics and Astrophysics using Pulsars and the SKA Jim Cordes Cornell U. Vicky Kaspi McGill U. Michael Kramer Jodrell Bank