pulsar rotation measures and galactic magnetic fields

JinLin HanJinLin HanNational Astronomical ObservatoriesNational Astronomical ObservatoriesChinese Academy of SciencesChinese Academy of Sciences Beijing 100012, ChinaBeijing 100012, [email protected]@bao.ac.cn

P. DemorestP. Demorest

Grateful Grateful to to cooperatorscooperators

Pulsar Rotation Measures and Galactic Pulsar Rotation Measures and Galactic Magnetic fieldsMagnetic fields

R.N. Manchester W. van Straten A.G. Lyne G.J. Qiao K. FerrierR.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.

OutlinesOutlines

Pulsar Distribution in the sky

Galactic Distribution of Pulsars: How do you get Distances?

Interstellar medium:Interstellar medium:

Clouds & large-scale structure?

Interstellar medium:Interstellar medium:

Clouds and turbulent structure ?

Ionized Interstellar MediumIonized Interstellar Medium + + moving pulsarsmoving pulsars

WHAM survey

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

Effects of Interstellar Medium• DM ds ne Dispersion Measure

• EM ds ne2 Emission Measure

• RM ds neBRotation 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

Dispersion Measures

DM

Galactic Latitude

DM = 20 cosec b

b H

L

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 = NeL

< Ne H cos(b)

Dispersion & IndependentIndependent Pulsar DistancesPulsar Distances

Indep. Dist. ObsIndep. Dist. Obs NumberNumber CommentsComments

Parallaxes:Interferometry timing optical

~13 ~ 5 ~ 1

1 mas @ 1 kpc1.6 s @ 1 kpcHST, point spread function

Associations SNRs 8GCs 16LMC,SMC ~8

false associations

HI absorption 74 bright pulsars, galactic rotation model

DM + ne model

all radio pulsars (~ 1400)

ISM perturbations

0

Dist

eDM n dlIndependent DistIndependent Dist + DM | + DM | i=1,Ni=1,N Ne2001 model Ne2001 model

Ne2001 model + DM Ne2001 model + DM Dist? Dist?

NE2001• Goal is to model ne(x) and Cn

2(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

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 Ne2001 model + DM

Dist?Dist?

We have to update it!

Dist

eee

dlnBlncm

eRM

0

Sun

PSR ||42

3

820.0)(2

dlB(l)

Pulsars as best probes for Galactic B-fieldPulsars 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

0

Dist

eDM n dl

sec103.83

3

MHz

DMt

22

21

21

PAPA

RM

GDM

RMB 232.1|| ＝

RM>0, field toward us

Pulsars: Best probes for Galactic magnetic fieldPulsars: 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 GalaxyWhy 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 v2/2 B~106G, ρ=1024gcm-3, v=10km s-1

(eg. Boilers & Cox 1990 for details)

• Key infoKey info for cosmic rays – propagation! for cosmic rays – propagation!• Foreground for CMB?! Foreground for CMB?! Thanks to WMAPThanks to WMAP

To understand the Galactic B-field, we have to measure first !To understand the Galactic B-field, we have to measure first !

Knowledge on the Galactic B-field is far from complete!Knowledge on the Galactic B-field is far from complete!






OutlinesOutlines

Paired Paired probes to probes to measuremeasure B-field in a region B-field in a region

GDM

RMB

dd

232.1

21|| ＝RM ∝ ∫ ne B// ds DM ∝ ∫ ne ds

Analysis is not limited to modeling B all the pathmodeling B all the path, but can measure B in the regionmeasure B in the region between! Significant improvement!Significant improvement!No worry about foreground bubbles! Less sensitive on Dist!

d1d2

d1 d2

If many pairs, do average, or

Fit together!

**SunSun

**SunSun

Major observations of pulsar RMsMajor observations of pulsar RMsAuthorsAuthors No. of RMsNo. of RMs No. No. New RMsNew RMs

Hamilton & Lyne (1987)Hamilton & Lyne (1987) 163163 119119

Rand & Lyne (2004):Rand & Lyne (2004): 2727 2727

Qiao et al. (1995)Qiao et al. (1995) 4848 3333

Han et al. (1999)Han et al. (1999) 6363 5454

Weisberg et al. (2003)Weisberg et al. (2003) 3636 1717

Han et al. (2006):Han et al. (2006): 223 223 196196

Noutsos et al. (2008)Noutsos et al. (2008) 150150 4343

Han et al. (2010 to submit!):Han et al. (2010 to submit!): 477477 400 400

1st b

ig ste

p!

2nd big

step!

2nd big

step!

>50

0 hou

rs

>500 h

ours

at P

arkes

at P

arkes

Pulsar RMs observed by others

|b| < 8 degree

63+223 RMs by Parkes 63+223 RMs by Parkes (Han et al. (Han et al. 1999, 20061999, 2006))

|b| < 8 degree

|b| < 8 degree

63+223+477 RMs by Parkes +GBT63+223+477 RMs by Parkes +GBT(Han et al. 1999, 2006, (Han et al. 1999, 2006, 20092009))

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 Paired probes to probes to measuremeasure B-field in a region B-field in a region

GDM

RMB

dd

232.1

21|| ＝RM ∝ ∫ ne B// ds DM ∝ ∫ ne ds

Analysis is not limited to modeling B all the pathmodeling B all the path, but can measure B in the regionmeasure B in the region between! Significant improvement!Significant improvement!No worry about foreground bubbles! Less sensitive on Dist!

d1d2

d1 d2

If many pairs, do average, or

Fit together!

MeasuringMeasuring the B-field in the Norma arm the B-field in the Norma armred: new measurements by Parkes 64m telescope

Han et al. 2002,Han et al. 2002,

ApJ 570, L17ApJ 570, L17

MeasuringMeasuring B-field in B-field in tangential regions!tangential regions!

GDM

RMB

232.1＝

Random B causing Random B causing the scattering of data, the scattering of data, gives uncertainties gives uncertainties

of <B>of <B>

(Han et al. 2006, ApJ 642, 868)(Han et al. 2006, ApJ 642, 868)

MeasuredMeasured magnetic field in the Galactic diskmagnetic field in the Galactic diskby pulsar RM/DMby pulsar RM/DM (Han et al. 2006, ApJ 642, 868)(Han et al. 2006, ApJ 642, 868)

• always always counterclockwise counterclockwise in arm region!in arm region!• clockwiseclockwise in interarm region ? in interarm region ?• More data still needed!More data still needed!

Measured Measured Radial dependence of regular field strengthRadial dependence of regular field strength

kpc7.45.8

G3.01.2

])(

exp[

0

0regular

B

B

R

BR

RRB(R)B

＝

Uncertainties reflect random fields!

GDM

RMB

232.1＝

(Han et al. 2006, ApJ 642, 868)(Han et al. 2006, ApJ 642, 868)

RMs from RMs from radio radio sources sources behind the behind the Galactic plane: Galactic plane: Consistent with B-Structure from pulsar data!Consistent with B-Structure from pulsar data!

Haverkorn et al. 2006Haverkorn et al. 2006

Brown et al. 2007Brown et al. 2007• PSR and EGRs data show PSR and EGRs data show a consistent B-structure!a consistent B-structure!• Dominant RM contribution Dominant RM contribution from tangential regions!from tangential regions!

Han et al. 2006Han et al. 2006

Han et al. 2010, ApJHan et al. 2010, ApJ to be submittedto be submitted 。。 1024 Pulsar RMs 1024 Pulsar RMs

RMs of radio sources

Behind disk!

Pulsar RMs

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

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

MeasuredMeasured B-structure in the Galactic diskB-structure in the Galactic disk


RMs of background radio sourcesfor B-field

in the GC region(Roy et al. 2008)

Sun

MeasuredMeasured B-structure in the Galactic diskB-structure in the Galactic disk


√

√ X?






OutlinesOutlines

Measuring the B-field fluctuationfluctuation vs scalesscales

PSR

Sun e dllBlnRM )()( ||

Many Simulations of dynamosMany Simulations of dynamos---- ---- check check spatial B-energy spectrumspatial B-energy spectrum & its & its evolution evolution e.g. Magnetic energy distribution on different spatial scalese.g. Magnetic energy distribution on different spatial scales (k=1/λ) (k=1/λ)

Many papers by 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 No measurements of the B-energy spectrum !spectrum !

Spatial magnetic energy spectrum of our GalaxySpatial magnetic energy spectrum of our Galaxy (Han et al. 2004, ApJ 610, 820)(Han et al. 2004, ApJ 610, 820)

Minter & Spangler Minter & Spangler 19961996

By pulsar By pulsar

RM/DMRM/DM

Email from A. MinterEmail from A. Minter

λ< ~4pc: 3D Kolmogorov80>λ> ~4pc: 2D turbulence?

Flatter B-energy spectrum Flatter B-energy spectrum at scales larger than the at scales larger than the ISM energy-injection-ISM energy-injection-scale!scale!






OutlinesOutlines

Milky Way: The largest edge-on Galaxy in the sky

Pulsars and extragalactic radio sources as probes

RM<0 : <B> away from us

RM>0 :<B> to us

RM Sky: RM Sky: Anti-symmetry!Anti-symmetry! Outliers significantly different from surroundings been Outliers significantly different from surroundings been

filteredfiltered

source

Sun eobse

lnl

cm

eRM dlB(l))(]

)([

22

42

3

+ --

-- +

Anti-symmetric RM sky: Anti-symmetric RM sky: A0 dynamoA0 dynamo?? (Han et al. 1997, A&A 322, 98)(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 The first dynamo mode identified on galactic identified on galactic scalesscales

Sun

RM sky: AntisymmetryAntisymmetry is confirmed!Notice: RM estimated from only 2 IFs of NVSS data

Individually: cannot trust! Collectively: Ok!

Taylor et al. (2009)

+ --

-- +?

RMRMobsobs = = RMRMintrinsicintrinsic + RM+ RMInterGalactic InterGalactic + + RMRMMilkyWayMilkyWay

• RMRMintrinsicintrinsic : RM intrinsic to the source; : RM intrinsic to the source;– They never know each other: They never know each other: uncorrelated uncorrelated Random! Random!– Location of emission regions: Location of emission regions: Beam size? Beam size?

• RMRMInterGalactic InterGalactic : RM from intergalactic space;: RM from intergalactic space;– weak correlated if with same intervening mediumweak correlated if with same intervening medium– Small values ??Small values ??

• RMRMMilkyWayMilkyWay : Foreground RM from our Galaxy; : Foreground RM from our Galaxy;– Correlated ~10Correlated ~10oo with same intervening ISM with same intervening ISM– Strongly depends on the Galactic coordiantes!Strongly depends on the Galactic coordiantes!

RMs of Extragalactic radio sourcesRMs of Extragalactic radio sources

source

Sun eobse

lnl

cm

eRM dlB(l))(]

)([

22

42

3

Common term!Common term!

Unique measurement

of Vertical B-component

Bv ＝ 0.

2 ～ 0.3G pointing from SGP to NGP (Effect of the NPS discounted already!)

Local vertical components: fromLocal vertical components: from poloidal field?poloidal field?

South Galactic Pole

North Galactic Pole

(see Han & Qiao 1994; Han et al. 1999)

Mao et al. 2010 ApJ

Preferably positive

Preferably negative

MeasuredMeasured B-strength in halo by B-strength in halo by 285 pulsars285 pulsars


GDM

RMB

232.1|| ＝


MeasuredMeasured B-strength in halo by B-strength in halo by 285 pulsars285 pulsarsG

DM

RMB

232.1|| ＝

MeasuredMeasured B-strength in halo by B-strength in halo by 285 pulsars285 pulsarsG

DM

RMB

232.1|| ＝

B~ 1-2 uG

B~ 1-2 uG






OutlinesOutlines

Connection of Galactic B-fields Connection of Galactic B-fields of large and small scalesof large and small scales

Beck et al. 1991, IAUS 146, 209

Connection of Galactic B-fields Connection of Galactic B-fields of large and small scalesof large and small scales

Li et al. 2006: Li et al. 2006: ApJ 648, 340ApJ 648, 340

(Results of SPARO 2003(Results of SPARO 2003)

• Mapped large-scale Mapped large-scale magnetic fields in four magnetic fields in four GMCsGMCs

• Statistically significant Statistically significant correlation with the correlation with the orientation of the Galactic orientation of the Galactic plane. plane.

• Field direction tends to be Field direction tends to be preserved during the preserved during the process of GMC formation.process of GMC formation.

Galactic plane

B-field from maser spotsB-field from maser spots Han & Zhang (2007, A&A 464, 609) Han & Zhang (2007, A&A 464, 609)

• Collect Zeeman splitting data of maser Collect Zeeman splitting data of maser spots in HII and star formation regionsspots in HII and star formation regions

• Spots in one region always have the saSpots in one region always have the same field orientation! me field orientation!

The Galactic distribution of Zeeman dataThe Galactic distribution of Zeeman dataSStructure tructure in distribution of in distribution of field directionsfield directions

Red: Clockwise field

Blue: Counterclock-wise field

We need more data, and better determined distances!

Han & Zhang 2007Han & Zhang 2007 A&A 464, 609A&A 464, 609

In situIn situ au-scaleau-scale-B-B correlated correlated withwith kpckpc-B-B! ! RReversalseversals: preserved from ISM to maser core: preserved from ISM to maser core!!






OutlinesOutlines

Pulsar birth & SN explosion

Asymmetric explosion gives

kick velocity!

Measured <V2D> = 211 km s-1

<V3D> = 4<V2D>/ = 2<V1D>

(Hobbs et al. 2005)

Guitar Nebula

PSR B2224+65

(Cordes et al. 2003)

Ionized Interstellar MediumIonized Interstellar Medium + + moving pulsarsmoving 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 ~ so / V rms flux ~ mean flux

– Refractive ISS r ~ L scatt / V rms flux < mean flux

For typicalpulsar distance:

td ~ 5-50 min (f+1.2) d ~ DMx (fGHz)4.4

tr ~ 5-100 days (f-2.2 ) r ~ fo

For an extended scattering medium x ~ 2.2 but in observations of pulsars x ~ 2 - 4

Scattering Disc and Refractive ISS

d

L

Sr=Ld

When the screen has a wide range of scales, the largest scale that can cause a fluctuation in amplitude is Ld = sr

This is called refractive scintillation

Angular broadening of a point radio sourceAngular broadening of a point radio source

330MHz 610MHz

Scattering and pulse-broadening

0.43 1.18 1.48 2.4 GHz0.43 1.18 1.48 2.4 GHz Mitra & Ramachandran (2001):4.4356.15 )101.31(105.4 DMDMsc

Scattering and pulse-broadening

Bhat et al. 2004

B1838-04

Scattering and Polarization ???

Li & Han 2002

B1841-05

Li & Han 2002

Scattering and Polarization ???






OutlinesOutlines

Done!

Thanks !Thanks !

pulsar rotation measures and galactic magnetic fields

Documents