A New Pulsar Distance Scale and its Implications

J. M. Cordes, Cornell Universitycordes@astro.cornell.eduCOSPAR 11 October 2002

• New electron density model (ne & ne) • How is it different from Taylor & Cordes ’93 and other models?• Ingredients and performance• Implications:

– Pulsar searches– Pulsar velocities– Luminosities (radio, X-ray, -rays)

• VLBI astrometry = breakthrough• Arecibo + GBT + VLA + Effelsburg + Jodrell = parallax machine• Square Kilometer Array = Mother of all parallax machines

w/ J. Lazio, S. Chatterjee, Z. Arzoumanian, D. Chernoff

New Model = NE2001Cordes & Lazio

Paper I = the model (astro-ph July ’02)

Paper II = methodology & particular lines of sight

Code + driver files (and paper I):www.astro.cornell.edu/~cordes/

Why detailed modeling?• Distance scale for neutron stars

– Neutron star populations (space density, luminosities)– Birth/death rates– Correlations with supernova remnants

• Turbulence in Galactic plasma• Galactic magnetic fields (deconstructing Faraday

rotation measures)• Interpreting scintillations of sources at

cosmological distances (AGNs, GRBs)• Baseline model for exploring the intergalactic

medium (dispersion & scattering in ISM, IGM)

Integrated Measures

• DM ds ne Dispersion Measure

• EM ds ne2 Emission Measure

• RM ds ne B 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

Integrated Measures

• DM ds ne Dispersion Measure

• EM ds ne2 Emission Measure

• RM ds ne B 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

Integrated Measures• DM ds ne Dispersion Measure

• EM ds ne2 Emission Measure

• RM ds ne B 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

Modeling the Galactic ne & ne

• mean & fluctuations are modelled

• dSM = Cn2 ds F ne

2 ds F ne dDM F = “fluctuation parameter” varies widely over Galaxy

• ne ~ Cn (outer scale)1/3

• possible/probable ne / ne ~ 1

• not clear that ne on all scales due to same process

Electron density of TC93

Taylor & Cordes (1993 ApJ, 411, 674)

Deficiencies of TC93

• DM too small for distant, high latitude objects• Distances overestimated for many objects in the

Galactic plane (10% of now-known objects have DMs too large to be accounted for)

• Pulse broadening over/underestimated in some directions

• Spiral arms incompletely defined over Galaxy• No Galactic center component

NE2001 • x2 more lines of sight (D,DM,SM) [114

with D/DM, 471 with SM/D or DM] (Parkes MB in next version)

• Local ISM component (new)[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’ of enhanced DM/SM (new)[5 parameters per clump] (Voids also)

• Improved fitting method (iterative likelihood analysis)penalty if distance or SM is not predicted to within the errors

Independent Pulsar Distances

• Parallaxes: Pulse timing Interferometry

• Associations: Supernova remnants Globular clusters

• HI Absorption: Galactic rotation

Very Long Baseline Array

PSR B0919+06S. Chatterjee et al. (2001) = 88.5 0.13 mas/yr = 0.83 0.13 mas

D = 1.2kpcV = 505 km/s

Brisken et al.

2001; 2002

Model Components

Galactic Center Component

Thin disk

Thick disk (1 kpc)

Spiral arms

DM vs Galactic longitude for different latitude bins

DM vs Galactic longitude for different latitude bins

134 of 1143 TC93 distances are lower bounds

DM(psr)-DM(model, )

Asymptotic DM

Differential TOA from Multipath:

Quenching of pulsations for d > P.

Pulsar Velocities• Lyne & Lorimer 1994:

• Proper motions + TC93 <V> ~ 500 km/s

• Unimodal distribution

• Cordes & Chernoff 1997:• MSP analysis (TC93) <V> ~ 80 km/s

• Cordes & Chernoff 1998: • High-field pulsars (TC93), < 10 Myr, 3D velocities (z/t)

• No correction for selection effects bimodal V, 1~ 175 km/s, 2~ 700 km/s (14%)

• Arzoumanian, Chernoff & Cordes 2002:• Full analysis (beaming, selection effects, TC93) bimodal V, 1~ 90 km/s, 2~ 500 km/s (40%)

ACC ‘02

How might the results change using NE2001 instead of TC93?

Guitar Nebula & PSR B2224+65

Edot ~ 1033 erg/s P~0.6 sec

D(TC93) = 2 kpc V~1700 km/s

D(NE2001) = 1.7 kpc V~1450 km/s

H Palomar 5-m image

Is the DM distance Realistic?

Is the DM distance Realistic? Yes

Standoff radius and flux are consistent

Pulsar velocities using only objects with parallax measurements

Distribution shows high-velocity tail and is “not inconsistent” with ACC results on high-field pulsars and CC97 on MSPs

New Parallax Programs

• 53 pulsars using VLBA antennas only at 1.4 GHz (systematics: ionospheric phase)

• Chatterjee, Brisken et al. (2002-2004)

• Currently can reach ~ 2 kpc

• 6 strong pulsars, VLBA-only at 5 GHz • Ionosphere less important

• Chatterjee, Cordes et al. (2001-ongoing)

• VLBA + Arecibo + GBT + … • Initial tests

• Expect to do ~100 pulsars in 5 years, some to 5 kpc

• Future: SKA superior phase calibration, sensitivity, can reach >10 kpc

Parkes MB Feeds

Arecibo Multibeam Surveys

I. Arecibo Galactic-Plane Survey

• |b| < 5 deg, 32 deg < l < 80 deg

• 1.5 GHz total bandwidth = 300 MHz

• digital correlator backend (1024 channels)(1st quadrant available = WAPP)

• multibeam system (7 feeds)

• ~300 s integrations, 3000 hours total

• Can see 2.5 to 5 times further than Parkes(period dependent)

• Expect ~500 to 1000 new pulsars

II. High Galactic Latitude Survey

• Millisecond pulsars(z scale height ~ 0.5 kpc)

• High-velocity pulsars (50% escape) (scale height = )

• NS-NS binaries (typical z ~ 5 kpc)

• NS-BH binaries (typical z ~ few kpc ?)

Search for:

Surveys Surveys with Parkes, with Parkes, Arecibo & Arecibo & GBT.GBT.

Simulated & Simulated & actualactual

Yield ~ 1000 Yield ~ 1000 pulsars.pulsars.

SKA pulsar SKA pulsar surveysurvey

600 s per 600 s per beambeam

~10~1044 psr’s psr’s

Comments & Summary• NE2001 = large improvement over TC93

• Caveat: HII regions, etc are grossly undersampled by the available LOS

• Need ~ 104 DMs to adequately model the MW

• VLBI (esp. with Arecibo, GBT, Jodrell, Effelsberg, etc) will yield many new parallaxes, obviating the need for DM distances for ~100 pulsars in a few yr

• New pulsar surveys will double sample in ~ 5 yr• Other distance approaches possible (radio =

standard candles if beaming accounted for)

• Expect tighter LX , L with better distance models.

NE2001 Spiral Arms

Electron density (log gray scale to enhance local ISM)

Electron density of TC93

Taylor & Cordes (1993 ApJ, 411, 674)

Deficiencies of TC93

• DM too small for distant, high latitude objects• Distances overestimated for many objects in

the Galactic plane (10% of now-known objects have DMs too large to be accounted for)

• Pulse broadening over/underestimated in some directions

• Spiral arms incompletely defined over Galaxy• No Galactic center component

Modeling the Galactic ne & ne

• mean & fluctuations are modelled

• dSM = Cn2 ds F ne

2 ds F ne dDM F = “fluctuation parameter” varies widely over Galaxy

• ne ~ Cn (outer scale)1/3

• possible/probable ne / ne ~ 1

• not clear that ne on all scales due to same process

INTERSTELLAR DISPERSIONINTERSTELLAR DISPERSION

DM = 0D ds ne(s)

Known for ~1200 pulsars

DM ~ 2 to 1100 pc cm-3

Variable at ~10-3 pc cm-3

Variations with d,l,b show obvious Galactic structure

Interstellar Scattering Effects Used

• Angular broadening (seeing)

• Pulse broadening

• Diffractive interstellar scintillations (DISS)d = / ld , ld = diffraction scale

=> Scattering Measure SM

Estimated Wavenumber Spectrum for ne

Similar to Armstrong, Rickett & Spangler (1995)

Slope ~ -11/3

Spectrum = Cn2 q-

SM = LOS integral of Cn

2

Independent Pulsar Distances

• Parallaxes: Pulse timing Interferometry

• Associations: Supernova remnants Globular clusters

• HI Absorption: Galactic rotation

Very Long Baseline Array

PSR B0919+06S. Chatterjee et al. (2001) = 88.5 0.13 mas/yr = 0.83 0.13 mas

D = 1.2kpcV = 505 km/s

Independent Pulsar Distances

• Parallaxes: Pulse timing Interferometry

• Associations: Supernova remnants Globular clusters

• HI Absorption: Galactic rotation

Brisken et al.

2001

www.astro.cornell.edu/~shami/psrvlb

ne in local ISM (Brisken PhD thesis)

~ 50 nearby pulsars for future VLBI +AO+GBT parallaxes

Current features of local ISM in NE2001 model

Parallax distances estimated correctly by model

Current features of local ISM in NE2001 model

Parallax distances estimated correctly by model

DM vs Galactic longitude for different latitude bins

DM vs Galactic latitude for different longitude bins

SM vs latitude

NE2001 Spiral Arms

Electron density (log gray scale to enhance local ISM)

Selected ApplicationsGalactic pulsar populations

pulsar velocities

e.g. J1740+1000 = 114 kyr at

z ~ 0.4 kpc

Bow shock nebulae to probe

density variationsGuitar Nebula HST obs.

Galactic turbulence

anisotropy of fluctuations

relation to B and CR prop’n

IGM in local group

M33 giant pulses from

Crab-like pulsars DM,SM

IGM on cosmological scales

scattering/scint’n of AGNs

by intervening galaxies, Ly

clouds, turbulence in cluster

gas HII regions at EOR

GRB & IDV scintillations

source sizes vs. t

ambient medium

IGM

Scattering of high z AGNs: Interstellar + Intergalactic ?

-2.2

Lazio et al. (unpublished)

Surveys Surveys with Parkes, with Parkes, Arecibo & Arecibo & GBT.GBT.

Simulated & Simulated & actualactual

Yield ~ 1000 Yield ~ 1000 pulsars.pulsars.

SKA pulsar SKA pulsar surveysurvey

600 s per 600 s per beambeam

~10~1044 psr’s psr’s

Summary

• New electron density model (NE2001) to be released soon (paper draft, software)

• www.astro.cornell.edu/~cordes/NE2001(also web site at NRL with web-based tools)

• Large VLBI program initiating to measure PM, parallaxes out to 5 kpc in some cases

• IGM scattering: angular broadening vs. z

• Use bow shock nebulae to probe ne.

• PMB pulsars for next version of model

J1740+1000

Seen through NPS

Also AGNs with enhanced RISS

Dynamic spectrum (DISS)with time scale smaller than expected

z / s ~ 4000 km/s

H Images of Pulsar Bow Shocks

Guitar Nebula (1600 km/s)MSP J0437-47 (100 km/s)

NE2001 Spiral Arms

Electron density (log gray scale to enhance local ISM)

Hybrid ISS/VLBI Methods(Cordes & Rickett 1998, ApJ, 507,846)

• Exploit different D dependences of ISS and proper motion estimates of pulsar velocities:

V = D (proper motion)

V = A W(Dd1/2/ td A depends on wavenumber spectrum & spatial distribution

W depends on spatial distribution

• Can solve for (or constrain) D and W(D) (info on spatial distribution of ne)

Parkes MB Feeds

Arecibo Multibeam Surveys

I. Arecibo Galactic-Plane Survey

• |b| < 5 deg, 32 deg < l < 80 deg

• 1.5 GHz total bandwidth = 300 MHz

• digital correlator backend (1024 channels)(1st quadrant available = WAPP)

• multibeam system (7 feeds)

• ~300 s integrations, 3000 hours total

• Can see 2.5 to 5 times further than Parkes(period dependent)

• Expect ~500 to 1000 new pulsars

II. High Galactic Latitude Survey

• Millisecond pulsars(z scale height ~ 0.5 kpc)

• High-velocity pulsars (50% escape) (scale height = )

• NS-NS binaries (typical z ~ 5 kpc)

• NS-BH binaries (typical z ~ few kpc ?)

Search for:

NE2001 = New Model Cordes & Lazio (to be submitted [in 2001])

• x2 more lines of sight (D,DM,SM) [114, 931, 471 data points]

• Local ISM component (new)[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’ of enhanced DM/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

NE2001 Spiral Arms

Electron density (log gray scale to enhance local ISM)

INTERSTELLAR DISPERSIONINTERSTELLAR DISPERSION

DM = 0D ds ne(s)

Known for ~1200 pulsars

DM ~ 2 to 1100 pc cm-3

Variable at ~10-3 pc cm-3

Variations with d,l,b show obvious Galactic structure

Pulse broadening (recent Arecibo results, R. Bhat et al)

~ D2/2c -4

Low DM pulsar, no broadening High DM pulsar with broadening

Interstellar Scattering Effects• Angular broadening (seeing)• Pulse broadening• Diffractive interstellar scintillations (DISS)

d = / ld , ld = diffraction scale

• Refractive interstellar scintillations (RISS)r = k-1 = geometrical optics refraction

• TOA fluctuations (multiple effects)• Superresolution phenomena: stars twinkle, planets

don’t pulsars show DISS, AGNs don’t, GRBs do RISS: pulsars, AGNs, GRBs …

Pulse broadeningPulse broadening Pulse broadening vs DMPulse broadening vs DM

Angular broadeningAngular broadeningDiffractive Scintillation Diffractive Scintillation

Dynamic spectrumVisibility functions: