Pulsar Rotation Measures and Galactic Magnetic fields

1. Pulsar Rotation Measures and Galactic Magnetic fields Grateful to cooperators JinLin HanNational Astronomical ObservatoriesChinese Academy of SciencesBeijing 100012, China hjl@bao.ac.cn P. Demorest R.N. Manchester W. van Straten A.G. Lyne G.J. Qiao K. Ferrier

2. Outlines • Pulsars as probes for interstellar medium • Why to study magnetic fields • Pulsar RMs for Disk fields: Large-scale reversals • Field structure • Field strength • Field fluctuation • RM sky: Antisymmetry for Galactic halo fields • Confirmed • Measured by pulsar RM/DM • Small-scale and large-scale fields: connections • Zeeman B of masers ~?~ Large-scale B-field in disk • Scattering for polarized signal? Yes.

3. Pulsar Distribution in the sky

4. Galactic Distribution of Pulsars: How do you get Distances?

5. Interstellar medium: Clouds & large-scale structure?

6. Interstellar medium: Clouds and turbulent structure ?

7. Ionized Interstellar Medium + moving pulsars Warm ionized medium (WIM): n ~ 0.1 cm-3; T ~ 8000 K; f ~ 0.2 WHAM survey

8. Effects of Interstellar Medium • DMds ne Dispersion Measure • EMds ne2 Emission Measure • RM ds neB||Rotation Measure • SM ds Cn2 Scattering Measure Spectrum = Cn2 q-, q = wavenumber (temporal spectrum not well constrained,relevant velocities ~ 10 km/s) • = 11/3 (Kolmogorov value) Scales ~ 1000 km to > pc

9. If L > H cos(b) DM = Ne H cos(b) Ne H = 20 pc cm-3 If L < H cos(b) DM = NeL < Ne H cos(b) L b H Uniform slab of density Ne DM DM = 20 cosec b Galactic Latitude Dispersion Measures

10. Dispersion &IndependentPulsar Distances Independent Dist+ DM | i=1,N Ne2001 model Ne2001 model + DM  Dist?

11. NE2001 • Goal is to model ne(x) and Cn2(x)  Fne2(x)in the Galaxy • Input data = {DM, EM, SM, [DL, DU] = distance ranges} • Prior input: • Galactic structure, HII regions, spiral-arm loci • Multi- constraints on local ISM (H, NaI, X-ray) • Figures of merit: • N> = number of objects with DM > DM (model) (minimize) • Nhits = number of LOS where predicted = measured distance: d(model)  [DL, DU] (maximize) • L = likelihood function using distances & scattering (maximize) • Basic procedure: get distances right first, then get scattering (turbulence) parameters From J. Cordes

12. NE2001 • x2 more lines of sight (D,DM,SM)[114 with D/DM, 471 with SM/D or DM] (excludes Parkes MB obj.) • Local ISM component (new) (new VLBI parallaxes)[12 parameters] • Thin & thick disk components (as in TC93) [8 parameters] • Spiral arms (revised from TC93)[21 parameters] • Galactic center component (new) [3 parameters](+auxiliary VLA/VLBA data ; Lazio & Cordes 1998) • Individual clumps/voids of enhanced dDM/dSM (new) [3 parameters x 20 LOS] • Improved fitting method (iterative likelihood analysis) penalty if distance or SM is not predicted to within the errors From J. Cordes

13. Model Components We have to update it! Ne2001 model + DM  Dist?

14. Pulsars as best probes for Galactic B-field RM>0, field toward us • Polarized+no intrinsic RM: Faraday rotation: • ne:can be measured: • <==the delay tells DM • the rotation of position • angles tells RM value==> • Average field strength • can be directly derived

15. Pulsars: Best probes for Galactic magnetic field Widely spread in the Galaxy ! Parkes PSR survey 3-D B-field structure!

16. Why to study the B-field of our Galaxy • Galaxy: a necessary key step from Sun to Universe! • Important hints for B-origin: primordial or dynamo? • Important roles in star formation • Hydrostatic balance & stability in ISM: B2/8π= ρ v2/2B~106G, ρ=1024gcm-3, v=10km s-1 (eg. Boilers & Cox 1990 for details) • Key info for cosmic rays – propagation! • Foreground for CMB?!Thanks to WMAP To understand the Galactic B-field, we have to measure first ! Knowledge on the Galactic B-field is far from complete!

17. Outlines • Pulsars as probes for interstellar medium • Why to study magnetic fields • Pulsar RMs for Disk fields: Large-scale reversals • Field structure • Field strength • Field fluctuation • RM sky: Antisymmetry for Galactic halo fields • Confirmed • Measured by pulsar RM/DM • Small-scale and large-scale fields: connections • Zeeman B of masers ~?~ Large-scale B-field in disk • Scattering for polarized signal? Yes.

18. d1 d2 Paired probes to measure B-field in a region RM∝ ∫ ne B// ds DM∝ ∫ ne ds * Sun * Sun d2 If many pairs, do average, or Fit together! d1 Analysis is not limited to modeling B all the path, but can measure B in the region between!Significant improvement! No worry about foreground bubbles! Less sensitive on Dist!

19. Major observations of pulsar RMs 1st big step! 2nd big step! >500 hours at Parkes

20. Pulsar RMs observed by others |b| < 8 degree

21. 63+223 RMs by Parkes (Han et al. 1999, 2006) |b| < 8 degree

22. 63+223+477 RMs by Parkes +GBT(Han et al. 1999, 2006, 2009) |b| < 8 degree

23. Pulsar RMs observed by others |b| > 8 degree

24. 63+223 RMs by Parkes (Han et al. 1999, 2006) |b| > 8 degree

25. 63+223+477 RMs by Parkes +GBT(Han et al. 1999, 2006, 2009) |b| > 8 degree

26. d1 d2 Paired probes to measure B-field in a region RM∝ ∫ ne B// ds DM∝ ∫ ne ds d2 If many pairs, do average, or Fit together! d1 Analysis is not limited to modeling B all the path, but can measure B in the region between!Significant improvement! No worry about foreground bubbles! Less sensitive on Dist!

27. Measuring the B-field in the Norma armred: new measurements by Parkes 64m telescope Han et al. 2002, ApJ 570, L17

28. Measuring B-field in tangential regions! Random B causing the scattering of data, gives uncertainties of <B> (Han et al. 2006, ApJ 642, 868)

29. Measuredmagnetic field in the Galactic diskby pulsar RM/DM(Han et al. 2006, ApJ 642, 868) • always counterclockwise in arm region! • clockwise in interarm region ? • More data still needed!

30. Measured Radial dependence of regular field strength (Han et al. 2006, ApJ 642, 868) Uncertainties reflect random fields!

31. RMs from radio sources behind the Galactic plane: Consistent with B-Structure from pulsar data! Han et al. 2006 Haverkorn et al. 2006 • PSR and EGRs data show a consistent B-structure! • Dominant RM contribution from tangential regions! Brown et al. 2007

32. Han et al. 2010, ApJ to be submitted。 1024 Pulsar RMs Pulsar RMs RMs of radio sources Behind disk!

35. (Han et al. 2010, ApJ to be submitted。 1024 Pulsar RMs )

36. (Han et al. 2010, ApJ to be submitted )

37. MeasuredB-structure in the Galactic disk (Han et al. 2010, ApJ to be submitted )

38. RMs of background radio sourcesfor B-field in the GC region(Roy et al. 2008) Sun

39. MeasuredB-structure in the Galactic disk √ √ X? (Han et al. 2010, ApJ to be submitted )

40. Outlines • Pulsars as probes for interstellar medium • Why to study magnetic fields • Pulsar RMs for Disk fields: Large-scale reversals • Field structure • Field strength • Field fluctuation • RM sky: Antisymmetry for Galactic halo fields • Confirmed • Measured by pulsar RM/DM • Small-scale and large-scale fields: connections • Zeeman B of masers ~?~ Large-scale B-field in disk • Scattering for polarized signal? Yes.

41. Measuring the B-field fluctuation vs scales

42. Many Simulations of dynamos ---- check spatial B-energy spectrum & its evolution e.g. Magnetic energy distribution on different spatial scales (k=1/λ) • Many papers by • N.E. L. Haugen, A. Brandenburg, W. Dobler, ….. • A. Schekochihin, S.C. Cowley, S. Taylor, J. Moron, ….. • E. Blackman, J. Maron ….. • Others ….. No measurements of the B-energy spectrum !

43. Spatial magnetic energy spectrum of our Galaxy(Han et al. 2004, ApJ 610, 820) Email from A. Minter By pulsar RM/DM Flatter B-energy spectrum at scales larger than the ISM energy-injection-scale! Minter & Spangler 1996 λ< ~4pc: 3D Kolmogorov 80>λ> ~4pc: 2D turbulence?

44. Outlines • Pulsars as probes for interstellar medium • Why to study magnetic fields • Pulsar RMs for Disk fields: Large-scale reversals • Field structure • Field strength • Field fluctuation • RM sky: Antisymmetry for Galactic halo fields • Confirmed • Measured by pulsar RM/DM • Small-scale and large-scale fields: connections • Zeeman B of masers ~?~ Large-scale B-field in disk • Scattering for polarized signal? Yes.

45. RM Sky: Anti-symmetry!Outliers significantly different from surroundings been filtered RM<0 : <B> away from us + -- -- + RM>0 : <B> to us Milky Way: The largest edge-on Galaxy in the sky Pulsars and extragalactic radio sources as probes

46. Anti-symmetric RM sky: A0 dynamo?(Han et al. 1997, A&A 322, 98) Evidence for global scale • High anti-symmetry to the Galactic coordinates • Only in inner Galaxy • nearby pulsars show it at higher latitudes Implications • Consistent with field configuration of A0 dynamo • The first dynamo mode identified on galactic scales Sun

47. RM sky: Antisymmetry is confirmed! Notice: RM estimated from only 2 IFs of NVSS data Individually: cannot trust! Collectively: Ok! + -- -- +? Taylor et al. (2009)

48. RMs of Extragalactic radio sources RMobs =RMintrinsic+ RMInterGalactic+ RMMilkyWay • RMintrinsic : RM intrinsic to the source; • They never know each other: uncorrelated  Random! • Location of emission regions:  Beam size? • RMInterGalactic : RM from intergalactic space; • weak correlated if with same intervening medium • Small values ?? • RMMilkyWay : Foreground RM from our Galaxy; • Correlated ~10o with same intervening ISM • Strongly depends on the Galactic coordiantes! Common term!

49. Preferably positive Preferably negative Mao et al. 2010 ApJ Local vertical components: frompoloidal field? North Galactic Pole Unique measurement of Vertical B-component Bv＝0.2～0.3G pointing from SGP to NGP (Effect of the NPS discounted already!) South Galactic Pole (see Han & Qiao 1994; Han et al. 1999)

50. MeasuredB-strength in halo by 285 pulsars (Han et al. 2009, ApJ to be submitted )