A New Pulsar Distance Scale and its Implications
J. M. Cordes, Cornell [email protected] 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
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
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%)
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
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
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.
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.
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
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
Surveys Surveys with Parkes, with Parkes, Arecibo & Arecibo & GBT.GBT.
Simulated & Simulated & actualactual
Yield ~ 1000 Yield ~ 1000 pulsars.pulsars.
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
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)
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
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:
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