1. Relativistic Spin Precession in the Double Pulsar Victoria Kaspi McGill University R. Breton, V. Kaspi, M. Kramer, M. McLaughlin, M. Lyutikov, S. Ransom, I. Stairs, R. Ferdman, F. Camilo, A. Possenti, in preparation.

2. McGill PhD student Rene Breton Current and Recent Members of the McGill Pulsar Group

3. 2004: Double Binary Pulsar Discovered! Unprecedented laboratory for testing General Relativity

4. © 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

5. PSR J0737-3039 Kramer et al. 2006 Best strong-field GR test by far! Shapiro delay ‘shape’ parameter: s observed /s predicted = 0.99987  0.00050

6. 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

7. B Modulates A in Eclipse! McLaughlin et al. 2004 Phase of B shown with dashed lines Average eclipse, summed coherently with B phase

8. 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

9. B-Phase Resolved Eclipses R. Breton

10. Eclipse Model The 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.

11. Geometry for Double Pulsar Lyutikov & Thompson 2005 Show Movie

12. Pulsar A Eclipse Modelling Breton et al. in prep. A eclipse modulation offers new way to measure geometry precisely – can look for relativistic precession of B’s spin!

13. 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).

14. 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.

15. We piggy-back on long-term timing observations done at GBT, looking at eclipse data only. Presently have 63 eclipses, over 4 yr. Model fitting done on Beowulf-style mini- supercomputer (“the Borg”) at McGill.

16. 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

17. PRELIMINARY: Relativistic Spin Precession Detected Breton et al. in prep.

18. Results GR PREDICTION Breton et al. in prep.

19. Results, Differently Any successful theory of gravity in this framework must predict this value.

20. New GR Test Breton et al. In prep. Spin precession in alternate theories of gravity not worked out… our observation provides clear new constraint any theory must satisfy.

21. 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.