TESTING GR WITH PULSARS III NEW TESTS + THE FUTURE

Vicky Kaspi, McGill University Harvard/Smithsonian GR Conference May 2012

Outline

Eclipses in double pulsar and relativistic spin precession

New pulsar surveys

New exciting relativistic binary

The Double Pulsar at a Glance

Pulsar A: 23 ms (Burgay et al. 2003, Nature)

Pulsar B: 2.8 s (Lyne et al. 2004, Science)

2.4 hour orbital period

System viewed edge-on:

We see eclipse for 30 s each 2.4 hour orbit

Lyne et al. 2004, Kaspi et al. 2004

Pulsar A Eclipse

Pulsar A eclipsed for ~30s each orbit

Eclipse duration >> projected size of B’s surface

eclipse frequency independent, asymmetric GBT

B Modulates A in Eclipse!

McLaughlin et al. 2004

Phase of B shown with dashed lines

Average eclipse, summed coherently with B phase

Modulation at B’s Period During A’s Eclipse

Dynamic FFT of light curve of A

Shows modulation at B’s period (or at a harmonic)

Only occurs during eclipse

Breton et al. 2012

Eclipse behavior nearly radio-frequency independent

Main frequency effects at edges of eclipses

Breton et al. 2012

Periodicity within eclipses radio-frequency independent across 300-2000 MHz

Breton et al. 2012

Eclipse duration depends on phase of pulsar B

Breton et al. 2012

Breton et al. 2012

Eclipse Model

The Lyutikov & Thompson Model (2006): • Closed field lines within pulsar B magnetosphere are

populated with hot relativistic plasma Results in synchrotron absorption of pulsar A radio

emission Magnetic field configuration is a dipole truncated

outside some radius.

Constructing a model eclipse light curve requires evaluating the synchrotron opacity

along different lines of sight through the magnetosphere

Geometry for Double Pulsar

Lyutikov & Thompson 2005

Pulsar A Eclipse Modelling

Breton et al. 2008

A eclipse modulation offers new way to measure geometry precisely – can look for relativistic precession of B’s spin!

Precession of the spin angular momentum of a body is expected in relativistic systems.

The precession of pulsar B is predicted to be due to: 1. the orbital motion of pulsar B in a curved space-time

(geodetic precession aka de Sitter/Fokker precession),

2. the “frame-dragging” due to the translational orbital motion of pulsar A around the center of mass (Lense-Thirring precession).

In general theories of gravity, SO precession rate is (Damour & Taylor 1992):

Rewriting with observable timing parameters:

Yields a test of the strong-field parameters

Collected 63 eclipses over 4 years at Green Bank Telescope in collaboration with timing team

McGill PhD thesis of Rene Breton

Evolution of B’s Spin Axis

For each of 63 eclipses LT model was fit using Markov Chain Monte Carlo

3 free parameters:

Show Movie

, ,

Breton et al. 2008, Science

Relativistic Spin Precession Detected

Results

0 Bt

B yr

4 77 0 65

0 66. deg/.

.

B yr 50734 00007. . deg/

GR PREDICTION Breton et al. 2008

Compare with GPB: 0.0018 deg/yr

( ) . .c

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m

m

B

GR

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B

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23

2360677 000035

( ) . .

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obs

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0 46

0 49338

( )

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c

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2 0 94 013

Results, Differently

Any successful theory of gravity in

this framework must predict

this value.

Continued Monitoring?

In principle, longer baseline = better measurement

BUT systematics: B’s profile changing;

challenging to measure pulse phase

B has disappeared!! Perera et al. 2012

On-Going Radio Pulsar Surveys

Also all-sky HTRU Survey using Parkes, Effelsberg

GBT

Arecibo

GBNCC 350 MHz Survey

20 pulsars so far, including 3 MSPs

Interesting GBT Driftscan Binary Pulsar J0348+0432

Based on observational work by Ryan Lynch, Paulo Freire, John Antoniadis; theory by Norbert Wex

Work in preparation…all info preliminary

P=39 ms, Porb=2.4 hr

Highly relativistic!

WD companion, mass well determined from spectrum, models: 0.172+/-0.002 sm

WD absorption lines show orbital Doppler shifts

Preliminary!!!

White Dwarf Radial Velocities

Courtesy John Antoniadis

q=11.85+/-0.10

Preliminary!!!

J0348: Massive & Relativistic

Combination of q, Mc yields Mp=2.039 +/- 0.029 solar masses

Relevant to EOS; Demorest et al. 2010

J0348: first massive NS in relativistic orbit!

Also highly asymmetric binary, q=11.85

Can test GR in new regime!

Courtesy John Antoniadis

Preliminary!!!

Testing Dipolar Radiation Damping: tensor-scalar theories

Radio timing of pulsar at GBT, Arecibo determines relativistic parameter Pbdot = (0.035+/-0.05)x10^-12 (PRELIMINARY)

PSR J0348+0432:

Note that this is better constraint than expected from GW experiments (Damour & Esposito-Farese 1998)

A B

Preliminary!!!

Couresy N. Wex

J0348 and aLIGO/Virgo

To detect merging NS-binaries, need template as aLIGO/Virgo data noisy

More realistic template = greater sensitivity

Major effort to calculate post-Newtonian (PN) approximation to GR

But alternative tensor-scalar (TS) theories could pose problem with this strategy

GR

TS

Courtesy Norbert Wex

Number of cycles in the aLIGO/VIRGO band (10 – 1000 Hz)

GR TS GR - TS

0348 today

Merger of a 2 M NS and a 10 M

BH (fISCO = 366 Hz)

Figure courtesy Norbert Wex

PRELIMINARY

J0348:Good News for GWs

Binary pulsars are very useful for testing TS gravity

Was true for low-mass NSs (Damour & Esposito-Farese 1998)

Now true for high-mass NSs from J0348 (work in prep.)

Good news for calculating templates:

Limit from J0348 suggests assuming GR should work for massive NSs as well

Conclusions

Double pulsar system spectacular eclipses provide unique test of gravity theories…

But pulsar B is gone

Ongoing pulsar surveys are finding other interesting sources: E.g. PSR J0348+0432 – first massive NS in

relativistic binary

Sets strict limits on dipolar gravitational wave damping

Stay tuned for more!