The double pulsar as Jupiter: tomography of magnetosphere and a new test of General Relativity. Maxim Lyutikov (Purdue U.)

Transcription

1 The double pulsar as Jupiter: tomography of magnetosphere and a new test of General Relativity Maxim Lyutikov (Purdue U.)

2 The Double Pulsar: sixth most important scientific discovery of 2004 (Science) Parkes Multi-beam Survey; Burgay et al (2003) First ever double pulsar system (6 th double NS system) PSR J A: P=22 ms (old) PSR J B: P=2.7 s (young) P orb = 2.4-hr (pulsars separated by cm = 3 lt-s) Only ~ 1 kpc away, system observed nearly edge on (<0.5 o ) Allows Precise measurement of masses Testing GR (0.05% agreement) Possibly measuring I A (EOS) Direct probes of pulsar magnetosphere and plasma physics Parkes Multibeam Receiver

3 Discovery of A pulsar (Burgay, et al. 2003)

4 Formation & LIGO predictions M 1 >10M Sun SN 1 M 2 ~10M Sun Details are not clear ( population synthesis ) Rate of NS-NS coalecence increased by 10 times (Kalogera et al) Good for LIGO pulsar A X-ray binary millisecond PSR SN 2 pulsar B

5 Excellent test ground for GR 0737A Shapiro Delay at the GBT 5 min integrations A B (Ransom et al 04) Inclination = /- 1.5 (Kramer et al 06)

6 Test ground for GR System is over-constrained can be used to test GR. M A =1.3381(7) M Sun M B =1.2489(7) M sun Orbit shrinks by 7mm a day, a/d= s obs (100 ± 0.05)% exp s Different (non-radiative) test of GR than Hulse-Taylor Maybe possible to measure I A (from gravito-magnetic precession) ω = (7)deg/ yr (Lyne etal, 04, 05; Kramer 06) More on GR tests later

7 Direct probes of pulsar magnetosphere and plasma physics (and another GR test)

8 Part I: eclipse of A 8

9 A is eclipsed for ~30 sec each orbit Eclipse Rotational phase of A Light curve of A Orbital phase (Kaspi et al. 2004) Nearly frequency independent Full width ~ 2 x cm Asymmetric: long ingress sharp egress

10 A eclipse: modulated at B rotation Average at given orbital phase & phase of B Rotational phase Eclipse Light curve of A This clearly indicates that absorption of A radio emission is done inside pulsar B magnetosphere Orbital phase (McLaughlin et al, 2004) Modulation is at 0.5P B, P B and full eclipse after the conjunction Absorption when magnetic axis of B is pointing towards us

11 Magnetospheres of isolated pulsars (nearly) Dipole B-field Closed field lines R max < c P/2π Open field lines near magnetic pole Radio emission is generated near magnetic pole (D. Page)

12 Magnetosphere of B is modified by A wind Similar to Solar wind Earth Magnetosphere Pulsar A wind blows off pulsar B magnetosphere Bow shock, magnetospheath: Earth Sun www-istp.gsfc.nasa.gov

13 Pulsar A wind blows off most of B magnetosphere Edge of B magnetosphere: pressure balance between B-field and A wind B 2 8π = p a = L a 4πcD 2 A B ; B magsph = B NS ( ) 3 Rmagsph R NS Surface field? Isolated pulsars (dipolar losses, but not exactly ): B NS = P 19 P More open field lines than in isolated pulsars B NS = D1/2 L 3/4 B c = G L 1/4 A R3 NS Ω3/2 B Pulsar B R mag R magsph = ( LB ) 1/4 cda B A wind L A Ω B = cm R LC = Spitkovsky (2004) Lyutikov (2004)

14 Eclipses: how? n GJ = ΩB 2πec expected density Need frequency independent eclipse, size of eclipsing region is known Thomson scattering? R < cm, n ~ cm -3, λ ~ n/n GJ ~ unreasonable Cyclotron absoprtion? (very large cross-section) λ ~ 10 - reasonable But: ω=ω B (r) width of eclipse ~ υ -1/3 m, contrary e c to observations Synchrotron absorption, γ >> 1 ω k II v II = ω B γ ; ω = e B B broad range of frequencies ω B /γ< ω <ω B γ 2 Eclipse profile is determined mostly by geometrical factors Large(ish) cross-section B NO NO YES γ e - ω k II v II = ω B γ ; ω B = e B m e c

15 Model of eclipses There are open and closed field lines Closed field lines are dipolar Relativistic plasma, γ ~10, n Synchrotron absorption along closed field lines of a rotating dipole broad range of frequencies ω B /γ< ω <ω B γ 2 Eclipse profile is determined mostly by geometrical factors Large(ish) cross-section Parameters to be fitted : θ Ω, φ Ω orientation of Ω impact parameter z α ν = χ angle between Ω and μ en B sin χ Plasma density, normalized to n GJ,mag ( ωb sin χ Outer and inner radii of populated field lines R +, R_ γω ) 5/3

16 yellow: data (Mclaughlin et al), Red: model

17 17

18 Phase-dependent duration McLauphlin et al (2004) Phase 0, 180 Phase 90, 270 Phase 0, 180 Phase 90, 270

19 Nearly frequency independent This gives lower limit on density. Eclipse should become transparent at high υ

20 Parameters Ω B 60 o 75 o orbital plane μ sky θ Ω ~ 60 o (angle between orbital plane normal and Ω) expected due to kick at birth of B φ Ω 30 o (angle between plane of sky and Ω) χ~75 o degrees (angle between μ and Ω) close to orthogonal rotator n Density at R mag : n GJ R + = cm (expected cm) Need B-field ~ 10 times smaller Wrong calculation of a torque? Tiny I B }unlikely Particles diffuse inward due to break down of 3d adiabatic invariant, density increases n ~ 1/L 2 (similar to Jupiter)?

21 Predicted polarization signal I I unpol Q U V~ 0 Two modes with different absorption indeces α ν (1) =4 α ν /3, e-vector perp to k-b plane α ν (2) =2 α ν /3, e-vector in k-b plane Smooth variations of Π & position angle Highest Π in the middle, hard to detect A is polarized, need to know absolute PA wrt to orbital plane Observations are in progress (Stairs)

22 Large n~10 5 n GJ : hot particles are efficiently trapped in magnetosphere Synchrotron cooling: R cool ~ 10 8 cm ~ 0.05 R mag Most particles are reflected by magnetic bottling, only 10-6 reach cooling radius. At R mag particles live ~ 10 6 P B, density ~ n GJ,mag Need to re-supply at a rate ~ n GJ,mag per period

23 Predictions: change of eclipse profile due to geodetic precession (10-30 yrs)

24 Changes in eclipse profile 24

25 Geodetic precession Markov Chain Monte Carlo fit (Breton et al., Science, 2008) Angle of spin of B wrt line of sight Angles of spin of B wrt orbital plane and spin-b-moment: do not change 25

26 New test of GR Precession rate Double Pulsar Ω B = x A x B n 3 s 2 1 e c 2 σ B 2 G the first term accessible only for the GR predicts: Ω B = 5.07 / yr Observed: /yr (no predictions in others theories of gravity) C.f. Gravity Probe B, same accuracy 26

27 Part II: Orbital modulation of B emission 27

28 Orbital modulation of B emission Rotational phase of B Orbital phase B is bright at two orbital phases Orbit-dependent profile changes: from strong main pulse and weak precursor to roughlyequal double pulse. These patterns are stable across epoch and observing frequency. Idea: B is always bright, but its radiating beam misses the Earth most of the time

29 Distortion of deep B magnetosphere by A wind Beam of B is ~ 2 o Emission is generated deep in, R<R mag, near polar field line Polar field lines wobble a bit (~ 2 o ) around direction of magnetic axis, coming in and out of sight depending on orbital and rotational phase Distorted magnetosphere: (Earth-Solar wind) stretched dipole (Stern 86) tanθ polar = 1 C tanθ µ Wind of A towards tail

30 McLauphlin et al. in prog. 30

31 Distortion of B magnetosphere by the wind of A tanθ polar = 1 C tanθ µ, C ~ 0.7 At the emission site magnetosphere is 30% distorted emission is generated high up in the magnetosphere Model bright phases Trajectory of polar field line on sky Black: undistorted Green: φ orb =-π/4 Blue: φ orb =0 Red: φ orb = π/4 Observed bright phases

32 Implications/Prediction Different profiles at different orbital phases. Line of sight passes through different emission regions: probe of structure of emission region in one pulsar Orbital phase-dependent variation in arrival time (~ temporal noise if just averaged) Ransom 04 Model φ em (φ orb );

33 Secular evolution of B φ em (φ orb ) due to geodetic precession; Changes of profile: different cuts Ω B 60 o 75 o μ orbital plane sky Burgay et al 05

34 More detailed model of magnetosphere in progress: Using models of Earth magnetosphere (Tsyganenko) Line of sight makes different cut: probe emission geometry 34

35 Orbital dependent X-rays of B: double pulsar as Jupiter Reconenction: Dungeys model: field reversal in the wind occur on scales << magnetosphere Pellizzioni 08 X-ray Emission by trapped particles supplied by the wind. Cusp penetration is most efficient when magnetic moment of B is ``looking at A 35

36 Drifting sub-pulses of B: probes of relativistic reconnection, wind of A, location of emission generation in B Probe A wind via interaction with B magnetosphere drifting subpulses from reconnection Direction of B-field is important: MHD wave A ~1000 r LC of A E-field of the wind B Predicted arrival times of A pulses at B (McLaughin et al, 04) 3D field tracing

37 Lots can be done Wind - magnetosphere interaction/reconnection when B- field in the wind oscillates on scales << magnetosphere size and varying inclination angle reconnection/magnetospheric jitter overall distortions plasma penetration radiation by trapped particles Radial diffusion in co-rotating magnetosphere - testing density distribution Testing scaling relations over a much wider parameter range than that provided by Solar planets alone (geometry!). 37

38 38

39 Conclusion B-field is dipolar at ~ cm: direct confirmation of a long standing assumption in pulsar physics Reason for success: deviations from dipole are small Lots more to be done Test eclipse size vs magnetosphere size Probe location and shape of emission generation regions in B (!) Probe A wind via interaction with B magnetosphere X-ray emission from B (?) Using models of Earth magnetophere (Tsyganenko)