Pulsar Rotation Measures and Galactic Magnetic fields Grateful

Pulsar Rotation Measures and Galactic Magnetic fields Grateful to cooperators Jin. Lin Han National Astronomical Observatories Chinese Academy of Sciences Beijing 100012, China hjl@bao. ac. cn P. Demorest R. N. Manchester W. van Straten A. G. Lyne G. J. Qiao K. Ferrier

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: Antisymmetryfor 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.

Pulsar Distribution in the sky

Galactic Distribution of Pulsars: How do you get Distances?

Interstellar medium: Clouds & large-scale structure?

Interstellar medium: Clouds and turbulent structure ?

Ionized Interstellar Medium+ moving pulsars Warm ionized medium (WIM): n ~ 0. 1 cm-3; T ~ 8000 K; f ~ 0. 2 WHAM�

Effects of Interstellar Medium • • DM EM RM SM ds ne 2 ds ne. B|| ds Cn 2 Dispersion Measure Emission Measure Rotation Measure Scattering Measure Spectrum = Cn 2 q- , q = wavenumber (temporal spectrum not well constrained, relevant velocities ~ 10 km/s) = 11/3 (Kolmogorov value) Scales ~ 1000 km to > pc

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

Dispersion & Independent Pulsar Distances Independent Dist + DM | i=1, N Ne 2001 model + DM Dist? Indep. Dist. Obs Number Parallaxes: Interferometry timing optical Associations HI absorption DM + ne model ~13 ~5 ~1 Comments 1 mas @ 1 kpc 1. 6 s @ 1 kpc HST, point spread function SNRs 8 false associations GCs 16 LMC, SMC ~8 bright pulsars, 74 galactic rotation model all radio pulsars (~ 1400) ISM perturbations

NE 2001 • Goal is to model ne(x) and Cn 2(x) Fne 2(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 , Na. I, 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

NE 2001 • x 2 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 TC 93) [8 parameters] • Spiral arms (revised from TC 93) [21 parameters] • Galactic center component (new) [3 parameters] (+auxiliary VLA/VLBA data ; Lazio & Cordes 1998) • Individual clumps/voids of enhanced d. DM/d. SM (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

Model Components e v a h e ! t i e t a d p u to W Ne 2001 model + DM Dist?

Pulsars as best probes for Galactic B-field • 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 RM>0, field toward us

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

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: B 2/8π= ρ v 2/2 B~106 G, ρ=1024 gcm-3, v=10 km 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!

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: Antisymmetryfor 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.

Paired probes to measure B-field in a region RM ∝ ∫ n*e B// ds DM ∝ ∫ n* e ds Sun d 2 If many pairs, do average, or Fit together! d 1 d 2 Analysis is not limited to modeling B all the path, path but can measure B in the region between! Significant improvement! No worry about foreground bubbles! Less sensitive on Dist!

Major observations of pulsar RMs Authors Hamilton & Lyne (1987) Rand & Lyne (2004): Qiao et al. (1995) Han et al. (1999) Weisberg et al. (2003) Han et al. (2006): Noutsos et al. (2008) g i b t No. of RMs No. New RMs 163 119 27 27 48 33 63 54 36 17 223 196 150 43 477 400 ! ep st 1 s ! p e s t s r g u bi ho es d 0 rk n 2 50 Pa > t a Han et al. (2010 to submit!):

Pulsar RMs observed by others |b| < 8 degree

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

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

Pulsar RMs observed by others |b| > 8 degree

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

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

Paired probes to measure B-field in a region RM ∝ ∫ ne B// ds DM ∝ ∫ ne ds d 2 If many pairs, do average, or Fit together! d 1 d 2 Analysis is not limited to modeling B all the path, path but can measure B in the region between! Significant improvement! No worry about foreground bubbles! Less sensitive on Dist!

Measuring the B-field in the Norma arm red: new measurements by Parkes 64 m telescope Han et al. 2002, Ap. J 570, L 17

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

Measured magnetic field in the Galactic disk by pulsar RM/DM (Han et al. 2006, Ap. J 642, 868) • always counterclockwise in arm region! • clockwise in interarm region ? • More data still needed!

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

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

Han et al. 2010, Ap. J to be submitted。 1024 Pulsar RMs s u e rc io d ra so ! f k o s s di M R nd i h Be

(Han et al. 2010, Ap. J to be submitted。 1024 Pulsar RMs )

(Han et al. 2010, Ap. J to be submitted )

Measured B-structure in the Galactic disk (Han et al. 2010, Ap. J to be submitted )

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

Measured B-structure in the Galactic disk √ √ ? X (Han et al. 2010, Ap. J to be submitted )

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: Antisymmetryfor 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.

Measuring the B-field fluctuationvs scales

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 !

Spatial magnetic energy spectrum of our Galaxy (Han et al. 2004, Ap. J 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< ~4 pc: 3 D Kolmogorov 80>λ> ~4 pc: 2 D turbulence?

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: Antisymmetryfor 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.

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

Anti-symmetric RM sky: A 0 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 A 0 dynamo • The first dynamo mode identified on galactic scales Sun

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

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

Local vertical components: frompoloidal field? North Galactic Pole ����������������Unique measurement Preferably of Vertical B-component positive � Mao et al. 2010 Ap. J South Galactic Pole Preferably negative Bv＝ 0. 2～ 0. 3 G� pointing from SGP to NGP (Effect of the NPS discounted already!)� (see Han & Qiao 1994; Han et al. 1999)

Measured B-strength in halo by 285 pulsars (Han et al. 2009, Ap. J to be submitted )

Measured B-strength in halo by 285 pulsars (Han et al. 2009, Ap. J to be submitted )

Measured B-strength in halo by 285 pulsars B~ G u 1 -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: Antisymmetryfor 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.

Connection of Galactic B-fields of large and small scales Beck et al. 1991, IAUS 146, 209

Connection of Galactic B-fields of large and small scales Li et al. 2006: Ap. J 648, 340 (Results of SPARO 2003) 2003 • Mapped large-scale magnetic fields in four GMCs Galactic plane • Statistically significant correlation with the orientation of the Galactic plane. • Field direction tends to be preserved during the process of GMC formation.

B-field from maser spots Han & Zhang (2007 , A&A 464, 609 ) • Collect Zeeman splitting data of maser spots in HII and star formation regions • Spots in one region always have the same field orientation!

The Galactic distribution of Zeeman data Structure in distribution of field directions In situ au-scale-B correlated with kpc-B! Reversals: preserved from ISM to maser core! Blue: Counterclockwise field Red: Clockwise field Han & Zhang 2007 A&A 464, 609 We need more data, and better determined distances!

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: Antisymmetryfor 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.

Pulsar birth & SN explosion (Hobbs et al. 2005) Guitar Nebula Asymmetric explosion gives kick velocity! PSR B 2224+65 Measured <V 2 D> = 211 km s-1 <V 3 D> = 4<V 2 D>/ = 2<V 1 D> (Cordes et al. 2003)

Ionized Interstellar Medium+ moving pulsars Warm ionized medium (WIM): n ~ 0. 1 cm-3; T ~ 8000 K; f ~ 0. 2 WHAM�

Strong Interstellar Scintillation (ISS) • Below ~ 3 GHz. Interstellar Scintillation is strong, having an rms change in flux density > mean flux density • Two Time scales: – Diffractive ISS td ~ so / V rms flux ~ mean flux – Refractive ISS tr ~ L qscatt / V rms flux < mean flux For typical pulsar distance: td ~ 5 -50 min (f+1. 2) dnd ~ DMx (f. GHz)4. 4 tr ~ 5 -100 days (f-2. 2 ) dnr ~ fo For an extended scattering medium x ~ 2. 2 but in observations of pulsars x ~ 2 - 4

Scattering Disc and Refractive ISS Sr=Lqd L qd When the screen has a wide range of scales, the largest scale that can cause a fluctuation in amplitude is Lqd = sr This is called refractive scintillation

Angular broadening of a point radio source 330 MHz 610 MHz

Scattering and pulse-broadening

Scattering and pulse-broadening 0. 43 Bhat et al. 2004 1. 18 1. 48 2. 4 GHz Mitra & Ramachandran (2001):

Scattering and Polarization ? ? ? B 1838 -04 Li & Han 2002

Scattering and Polarization ? ? ? B 1841 -05 Li & Han 2002

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: Antisymmetryfor Galactic halo fields – Confirmed – Measured by pulsar RM/DM ! e n o D • Small-scale and large-scale fields: connections – Zeeman B of masers ~? ~ Large-scale B-field in disk • Scattering for polarized signal? Yes.

Thanks !