Relativistic Spin Precession in the Double Pulsar

Victoria KaspiMcGill University

R. Breton, V. Kaspi, M. Kramer, M. McLaughlin, M. Lyutikov, S. Ransom, I. Stairs, R. Ferdman, F. Camilo, A. Possenti, in preparation.

McGill PhD student Rene Breton

Current and Recent Members of the McGill Pulsar Group

2004: Double Binary Pulsar Discovered!

Unprecedented laboratoryfor testing General

Relativity

QuickTime™ and aYUV420 codec decompressor

are needed to see this picture.

© John Rowe Animation/Australia Telescope National Facility, CSIRO

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

PSR J0737-3039

Kramer et al. 2006

Best strong-fieldGR test by far!

Shapiro delay ‘shape’ parameter:

sobserved/spredicted = 0.99987 0.00050

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

R. Breton

B-Phase Resolved Eclipses

R. Breton

Eclipse ModelThe Lyutikov & Thompson Model (2006, ApJ):

• 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 &Thompson2005

ShowMovie

Pulsar A Eclipse Modelling

Breton et al.in prep.

A eclipsemodulationoffers newway to measuregeometry precisely – canlook for relativisticprecessionof 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, the precession rate is (Damour & Taylor, 1992, Phys. Rev. D):

For a very particular choice of observable timing parameters:

Yields a test of the strong-field parameters

Any other mixture of timing observables would include additional strong-field parameters.

We piggy-back on long-termtiming observations done atGBT, looking at eclipse data only.

Presently have 63 eclipses,over 4 yr. Model fitting doneon Beowulf-style mini-supercomputer (“the Borg”)at McGill.

Evolution of B’s Spin Axis• For each of 63 eclipses obtained in the past

~4 yr, we fit to the LT model using a Markov Chain Monte Carlo method

• 3 free parameters:

Show Movie

, ,

PRELIMINARY:

Relativistic Spin Precession Detected

Breton et al. in prep.

Results

0 B t

B yr 4 7 7 0 6 5

0 6 6. d eg/..

B yr 5 0 7 3 4 0 0 0 0 7. . d eg/

GR PREDICTIONBreton et al. in prep.

Results, Differently

( ) . .c

G

m

mB

G RA

B

2

23

23 6 0 6 7 7 0 0 0 0 3 5

( ) . ..c

GB

obs

2

0 4 60 4 93 3 8

( )

( )

. .

c

Gc

G

Bobs

BG R

2

2 0 9 4 0 1 3

Anysuccessfultheory ofgravity inthis frameworkmust predictthis value.

New GR Test

Breton et al.In prep.

Spin precessionin alternatetheories of gravitynot worked out…our observationprovides clear newconstraint anytheory must satisfy.

Continued Monitoring

• In principle, longer baseline means better measurement

• BUT systematics:– B’s profile changing;

challenging to measure pulse phase

– B may disappear entirely (though temporarily)

Breton et al. in prep.