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

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.Outlines

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 WHAM survey Warm ionized medium (WIM): n ~ 0.1 cm -3 ; T ~ 8000 K; f ~ 0.2

Effects of Interstellar Medium DM  ds n e Dispersion Measure EM  ds n e 2 Emission Measure RM  ds n e B  Rotation Measure SM  ds C n 2 Scattering Measure Spectrum = C n 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 DM Galactic Latitude DM = 20 cosec b b H L Uniform slab of density N e If L > H cos(b) DM = N e H cos(b) N e H = 20 pc cm -3 If L < H cos(b) DM = N e L < N e H cos(b)

Independent Pulsar Distances Dispersion & Independent Pulsar Distances Indep. Dist. Obs Number Number Comments Comments Parallaxes: Interferometry timing optical ~13 ~ 5 ~ kpc 1.6  1 kpc HST, point spread function Associations SNRs 8 GCs 16 LMC,SMC ~8 false associations HI absorption 74 bright pulsars, galactic rotation model DM + n e model all radio pulsars (~ 1400) ISM perturbations Independent Dist+ DM | i=1,N  Ne2001 model Independent Dist + DM | i=1,N  Ne2001 model Ne2001 model + DM  Dist?

NE2001 Goal is to model n e (x) and C n 2 (x)  Fn e 2 (x) in the Galaxy Input data = {DM, EM, SM, [D L, D U ] = 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) –N hits = number of LOS where predicted = measured distance: d(model)  [D L, D U ] (maximize) –L = likelihood function using distances & scattering (maximize) Basic procedure: get distances right first, then get scattering (turbulence) parameters From J. Cordes

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

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

Pulsars as best probes for Galactic B-field Polarized + no intrinsic RM: Faraday rotation: n e : 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~10 6 G, ρ=10 24 gcm -3, v=10km s-1 (eg. Boilers & Cox 1990 for details) Key info for cosmic rays – propagation!Key info for cosmic rays – propagation! Foreground for CMB?! Thanks to WMAPForeground 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!

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.Outlines

Paired probes to measure B-field in a region RM ∝ ∫ n e B // ds DM ∝ ∫ n e ds modeling B all the path measure B in the regionSignificant improvement! 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! d1 d2 d1d2 If many pairs, do average, or Fit together! *Sun*Sun

Major observations of pulsar RMs Authors No. of RMs No. New RMs No. New RMs Hamilton & Lyne (1987) Rand & Lyne (2004): 2727 Qiao et al. (1995) 4833 Han et al. (1999) 6354 Weisberg et al. (2003) 3617 Han et al. (2006): Noutsos et al. (2008) Han et al. (2010 to submit!): st big step! 2nd big step! >500 hours at Parkes >500 hours at Parkes

Pulsar RMs observed by others |b| < 8 degree

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

RMs by Parkes +GBT (Han et al. 1999, 2006, 2009)

Pulsar RMs observed by others |b| > 8 degree

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

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

Paired probes to measure B-field in a region RM ∝ ∫ n e B // ds DM ∝ ∫ n e ds modeling B all the path measure B in the regionSignificant improvement! 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! d1 d2 d1d2 If many pairs, do average, or Fit together!

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

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

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

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

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

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

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

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

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

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.Outlines

fluctuationscales Measuring the B-field fluctuation vs scales

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

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

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.Outlines

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

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 scalesThe first dynamo mode identified on galactic scales Sun

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

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

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

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

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

B~ 1-2 uG

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.Outlines

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: ApJ 648, 340 (Results of SPARO 2003 (Results of SPARO 2003) Mapped large-scale magnetic fields in four GMCs Mapped large-scale magnetic fields in four GMCs Statistically significant correlation with the orientation of the Galactic plane. Statistically significant correlation with the orientation of the Galactic plane. Field direction tends to be preserved during the process of GMC formation. Field direction tends to be preserved during the process of GMC formation. Galactic plane

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 Collect Zeeman splitting data of maser spots in HII and star formation regions Spots in one region always have the same field orientation! Spots in one region always have the same field orientation!

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

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.Outlines

Pulsar birth & SN explosion Asymmetric explosion gives kick velocity! Measured = 211 km s -1 = 4 /  = 2 (Hobbs et al. 2005) Guitar Nebula PSR B (Cordes et al. 2003)

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

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  d ~ s o / V rms flux ~ mean flux –Refractive ISS  r ~ L  scatt / V rms flux < mean flux For typical  pulsar distance: t d ~ 5-50 min (f +1.2 )  d ~ DM x (f GHz ) 4.4 t r ~ days (f -2.2 )  r ~ f o For an extended scattering medium x ~ 2.2 but in observations of pulsars x ~ 2 - 4

Scattering Disc and Refractive ISS dd L S r =L  d When the screen has a wide range of scales, the largest scale that can cause a fluctuation in amplitude is L  d = s r This is called refractive scintillation

Angular broadening of a point radio source 330MHz 610MHz

Scattering and pulse-broadening

GHz Mitra & Ramachandran (2001): Scattering and pulse-broadening Bhat et al. 2004

B Scattering and Polarization ??? Li & Han 2002

B Li & Han 2002 Scattering and Polarization ???

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.Outlines Done!

Thanks !