Astrometric Observations of Neutron Stars

Astrometric Observations of Neutron Stars Shami Chatterjee 21 July 2009

Overview Neutron Stars are laboratories for extreme physics.

Overview Neutron Stars are laboratories for extreme physics. We need precision measurements to exploit them.

Overview Neutron Stars are laboratories for extreme physics. We need precision measurements to exploit them. In this talk: Why bother with astrometry of Neutron Stars?

Overview Neutron Stars are laboratories for extreme physics. We need precision measurements to exploit them. In this talk: Why bother with astrometry of Neutron Stars? Case Study: High veocity pulsars. Case Study: Proper motion of a transient source.

Overview Neutron Stars are laboratories for extreme physics. We need precision measurements to exploit them. In this talk: Why bother with astrometry of Neutron Stars? Case Study: High veocity pulsars. Case Study: Proper motion of a transient source. Attaining high precision.

Overview Neutron Stars are laboratories for extreme physics. We need precision measurements to exploit them. In this talk: Why bother with astrometry of Neutron Stars? Case Study: High veocity pulsars. Case Study: Proper motion of a transient source. Attaining high precision. Results and future directions.

Neutron Star Astrometry Basic observable: Position θ. Celestial coordinate grid defined by the ICRF.

Neutron Star Astrometry Basic observable: Position θ. Celestial coordinate grid defined by the ICRF. Positions over time: Proper motion µ. Longer time baseline helps measurement. Reference frame and calibrator stability?

Neutron Star Astrometry Basic observable: Position θ. Celestial coordinate grid defined by the ICRF. Positions over time: Proper motion µ. Longer time baseline helps measurement. Reference frame and calibrator stability? Positions from different points in Earth s orbit: Parallax π. Frequent sampling over the orbit helps measurement.

Neutron Star Astrometry Optical / IR. (e.g., HST π to RX J0720.4 3125, Kaplan et al.) X-ray. (e.g., CXO µ of NS in Puppis A, Winkler & Petre.) Radio pulse timing of recycled pulsars. (e.g., J0437 4715; van Stratten, Bailes, et al.) Radio interferometry. The majority of NS parallaxes are from VLBI.

Neutron Star Astrometry Optical / IR. (e.g., HST π to RX J0720.4 3125, Kaplan et al.) X-ray. (e.g., CXO µ of NS in Puppis A, Winkler & Petre.) Radio pulse timing of recycled pulsars. (e.g., J0437 4715; van Stratten, Bailes, et al.) Radio interferometry. The majority of NS parallaxes are from VLBI.

Neutron Star Astrometry Optical / IR. (e.g., HST π to RX J0720.4 3125, Kaplan et al.) X-ray. (e.g., CXO µ of NS in Puppis A, Winkler & Petre.) Radio pulse timing of recycled pulsars. (e.g., J0437 4715; van Stratten, Bailes, et al.) Radio interferometry. The majority of NS parallaxes are from VLBI.

Neutron Star Astrometry Optical / IR. (e.g., HST π to RX J0720.4 3125, Kaplan et al.) X-ray. (e.g., CXO µ of NS in Puppis A, Winkler & Petre.) Radio pulse timing of recycled pulsars. (e.g., J0437 4715; van Stratten, Bailes, et al.) Radio interferometry. The majority of NS parallaxes are from VLBI.

Neutron Star Astrometry (Brisken et al. 2000 ++)

Neutron Star Astrometry (Brisken et al. 2000 ++) {µ,π} Model-independent distances and velocities.

Why do it? (What s in it for me?)

Why Measure Velocities and Distances? Astrophysics: NS atmospheres, cooling curves and nuclear Equations of State from spectra and absolute distances.

Why Measure Velocities and Distances? Astrophysics: NS atmospheres, cooling curves and nuclear Equations of State from spectra and absolute distances. (e.g., Lattimer & Prakash 2006, Yakolev et al. 2007)

Why Measure Velocities and Distances? Astrophysics: NS atmospheres, cooling curves and nuclear Equations of State from spectra and absolute distances. Astrophysics: Constraints on supernova core collapse. (e.g., Spruit & Phinney 1998, Deshpande et al. 1999, Lai et al. 2001, etc.)

Why Measure Velocities and Distances? Astrophysics: NS atmospheres, cooling curves and nuclear Equations of State from spectra and absolute distances. Astrophysics: Constraints on supernova core collapse. Origins: SNR associations and NS birth sites; true ages. (e.g., Hoogerwerf et al. 2000, Vlemmings et al. 2004, Blazek et al. 2006, etc.)

Why Measure Velocities and Distances? Astrophysics: NS atmospheres, cooling curves and nuclear Equations of State from spectra and absolute distances. Astrophysics: Constraints on supernova core collapse. Origins: SNR associations and NS birth sites; true ages. Evolution: NS distribution and population velocities. (e.g., Arzoumanian et al. 2001, Hobbs et al. 2005, Faucher-Giguère & Kaspi 2006, etc.)

Why Measure Velocities and Distances? Astrophysics: NS atmospheres, cooling curves and nuclear Equations of State from spectra and absolute distances. Astrophysics: Constraints on supernova core collapse. Origins: SNR associations and NS birth sites; true ages. Evolution: NS distribution and population velocities. Environment: Calibrate models of Galactic n e density. Environment: Model the local ISM with ISS, bow shocks. (e.g., Taylor & Cordes 1993, Cordes & Lazio 2001, etc.)

Why Measure Velocities and Distances? Astrophysics: NS atmospheres, cooling curves and nuclear Equations of State from spectra and absolute distances. Astrophysics: Constraints on supernova core collapse. Origins: SNR associations and NS birth sites; true ages. Evolution: NS distribution and population velocities. Environment: Calibrate models of Galactic n e density. Environment: Model the local ISM with ISS, bow shocks. Verify solar system extragalactic reference frame ties. (e.g., Bartel et al. 1996; also Fomalont & Reid 2007)

Case study: PSR B1508+55 How large are the kicks that NS receive at birth?

Case study: PSR B1508+55 How large are the kicks that NS receive at birth? B1508+55 is a very ordinary pulsar: Rotation period is 0.74 seconds. Inferred magnetic field is 2 10 12 Gauss. Characteristic age is 2.3 million years. Located well outside Galactic plane (b = 52.3 ).

Case study: PSR B1508+55 How large are the kicks that NS receive at birth? B1508+55 is a very ordinary pulsar: Rotation period is 0.74 seconds. Inferred magnetic field is 2 10 12 Gauss. Characteristic age is 2.3 million years. Located well outside Galactic plane (b = 52.3 ). Observe 8 times over 2 years with the VLBA...

Astrometric Results for B1508+55 µ a = 73.61 ± 0.04 mas yr 1 µ d = 62.62 ± 0.09 mas yr 1 π = 0.42 ± 0.04 mas (with Vlemmings, Brisken, Lazio, Cordes, Goss, Thorsett, Fomalont, Lyne, Kramer)

Astrometric Results for B1508+55 µ a = 73.61 ± 0.04 mas yr 1 µ d = 62.62 ± 0.09 mas yr 1 π = 0.42 ± 0.04 mas Distance = 2.37 +0.23 V = 1083 +103 90 0.20 kpc km s 1

Astrometric Results for B1508+55 µ a = 73.61 ± 0.04 mas yr 1 µ d = 62.62 ± 0.09 mas yr 1 π = 0.42 ± 0.04 mas Distance = 2.37 +0.23 V = 1083 +103 90 0.20 kpc km s 1 The highest measured model-independent velocity yet! (Chatterjee et al. 2005)

The Birth Site of B1508+55 Orbit of B1508+55 overlaid on Axel Mellinger s image of the Galaxy. Current Galactic latitude = 52.3. Trace back orbit in Galaxy: born in Galactic plane. Birth in or near Cygnus OB associations.

B1508+55: Getting its Kicks B1508+55: implied birth velocity 1100 km s 1. Binary disruption is unlikely to impart such a high velocity; a kick is required.

B1508+55: Getting its Kicks B1508+55: implied birth velocity 1100 km s 1. Binary disruption is unlikely to impart such a high velocity; a kick is required. Core collapse: first 3D hydrodynamic simulations (Fryer 2004) do not produce such large kicks. Work ongoing: better simulations, SASI, acoustic modes. (e.g., recent esults from various simulation groups: Janka et al., Fryer et al., Blondin et al., Burrows et al.)

B1508+55: Getting its Kicks B1508+55: implied birth velocity 1100 km s 1. Binary disruption is unlikely to impart such a high velocity; a kick is required. Core collapse: first 3D hydrodynamic simulations (Fryer 2004) do not produce such large kicks. Work ongoing: better simulations, SASI, acoustic modes. (e.g., recent esults from various simulation groups: Janka et al., Fryer et al., Blondin et al., Burrows et al.) High velocities impose severe constraints on core collapse and kick velocity scenarios.

Case study: A Magnetar Proper Motion If kicks are mediated by asymmetric neutrino emission, magnetic fields play a major role.

Case study: A Magnetar Proper Motion If kicks are mediated by asymmetric neutrino emission, magnetic fields play a major role. Experiment: Turn up the magnetic field. Are magnetar velocities ordinary psr velocities?

Case study: A Magnetar Proper Motion If kicks are mediated by asymmetric neutrino emission, magnetic fields play a major role. Experiment: Turn up the magnetic field. Are magnetar velocities ordinary psr velocities? Need X-ray or adaptive optics IR obs over many years. Interesting preliminary results. (e.g., two-epoch Chandra obs; Kaplan et al. 2009), But we need longer time baselines.

Magnetar XTE J1810 197 Camilo et al. (2006): Transient pulsed radio emission! Rapidly fading... (from Camilo et al. 2006)

Magnetar XTE J1810 197 Camilo et al. (2006): Transient pulsed radio emission! Rapidly fading... But bright enough for VLBA obs at 5, 8.4 GHz over 106 days.

A Magnetar Proper Motion µ α = 6.60 ± 0.06 mas yr 1 µ δ = 11.7 ± 1.0 mas yr 1 For D = 3.5 ± 0.5 kpc, V 220 km s 1 [180 270 km s 1 ] (Helfand, Chatterjee, et al. 2007)

A Magnetar Proper Motion µ α = 6.60 ± 0.06 mas yr 1 µ δ = 11.7 ± 1.0 mas yr 1 For D = 3.5 ± 0.5 kpc, V 220 km s 1 [180 270 km s 1 ] (Helfand, Chatterjee, et al. 2007) For this one magnetar V, no exotic kicks are required.

How do we do it?

Pulsar Astrometry with the VLBA Astrometric observations are phase-referenced: ICRF.

Pulsar Astrometry with the VLBA Astrometric observations are phase-referenced: ICRF. Boost S/N ratio for pulsars with the pulsar gate.

Pulsar Astrometry with the VLBA Astrometric observations are phase-referenced: ICRF. Boost S/N ratio for pulsars with the pulsar gate.

Pulsar Astrometry with the VLBA Astrometric observations are phase-referenced: ICRF. Boost S/N ratio for pulsars with the pulsar gate. Primary problem at 1.4 GHz: residual ionospheric effects.

Pulsar Astrometry with the VLBA Astrometric observations are phase-referenced: ICRF. Boost S/N ratio for pulsars with the pulsar gate. Primary problem at 1.4 GHz: residual ionospheric effects. PLot file version 1 created 16-NOV-1998 14:34:01 CONT: J0922+06 IPOL 1509.984 MHZ 0919-CL2.ICLN.2 PLot file version 1 created 16-NOV-1998 14:33:50 CONT: J0922+06 IPOL 1509.984 MHZ 0919-CL3.ICLN.1 330 330 320 320 310 310 300 300 MilliARC SEC 290 280 MilliARC SEC 290 280 270 270 260 260 250 250 240 240 250 240 230 220 210 200 190 180 MilliARC SEC Center at RA 09 22 13.98740 DEC 06 38 22.4440 Cont peak flux = 2.0358E-03 JY/BEAM Levs = 5.000E-04 * (-2, -1.40, -1, 1, 1.400, 2, 2.800, 4, 5.600, 8) 250 240 230 220 210 200 190 180 MilliARC SEC Center at RA 09 22 13.98740 DEC 06 38 22.4440 Cont peak flux = 3.7783E-03 JY/BEAM Levs = 5.000E-04 * (-2, -1.40, -1, 1, 1.400, 2, 2.800, 4, 5.600, 8) In-beam calibration enables sub-mas accuracy.

Pulsar Astrometry with the VLBA Astrometric observations are phase-referenced: ICRF. Boost S/N ratio for pulsars with the pulsar gate. Primary problem at 1.4 GHz: residual ionospheric effects. PLot file version 1 created 25-NOV-1998 14:38:24 CONT: J0922+06 IPOL 1509.984 MHZ 0919B-CL2.ICLN.1 PLot file version 1 created 25-NOV-1998 14:38:38 CONT: J0922+06 IPOL 1509.984 MHZ 0919B-CL3.ICLN.1 330 330 320 320 310 310 300 300 MilliARC SEC 290 280 MilliARC SEC 290 280 270 270 260 260 250 250 240 240 250 240 230 220 210 200 190 180 MilliARC SEC Center at RA 09 22 13.98740 DEC 06 38 22.4440 Cont peak flux = 1.1597E-03 JY/BEAM Levs = 5.000E-04 * (-2, -1.40, -1, 1, 1.400, 2, 2.800, 4, 5.600, 8) 250 240 230 220 210 200 190 180 MilliARC SEC Center at RA 09 22 13.98740 DEC 06 38 22.4440 Cont peak flux = 2.9278E-03 JY/BEAM Levs = 5.000E-04 * (-2, -1.40, -1, 1, 1.400, 2, 2.800, 4, 5.600, 8) In-beam calibration enables sub-mas accuracy.

A systematic approach to In-beam Calibration Image the VLA 1.4 GHz primary beam (25 ); Identify compact sources. CONT: B2045-16 IPOL 1464.119 MHZ B2045-16.ICL001.1 CONT: B2045-16 IPOL 1464.119 MHZ B2045-16.ICL011.1 CONT: B2045-16 IPOL 1464.119 MHZ B2045-16.ICL008.1-16 16 36-16 09 35-16 00 00 38 DECLINATION (J2000) 40 42 44 46 48 DECLINATION (J2000) 40 45 DECLINATION (J2000) 05 10 50 50 15 52 54 56 55 20 20 48 36.2 36.0 35.8 35.6 35.4 35.2 35.0 34.8 RIGHT ASCENSION (J2000) Cont peak flux = 4.7936E-03 JY/BEAM Levs = 4.794E-04 * (-4, -2, -1, 1, 2, 4, 8, 9.500) 20 48 37.6 37.4 37.2 37.0 36.8 36.6 36.4 36.2 36.0 RIGHT ASCENSION (J2000) Cont peak flux = 1.8890E-02 JY/BEAM Levs = 5.000E-04 * (-4, -2, -1, 1, 2, 4, 8, 16, 32) 20 48 50.4 50.2 50.0 49.8 49.6 49.4 49.2 49.0 RIGHT ASCENSION (J2000) Cont peak flux = 2.1737E-02 JY/BEAM Levs = 5.000E-04 * (-4, -2, -1, 1, 2, 4, 8, 16, 32 ) 63 target fields = 1060 sources detected ( 16 / field).

A systematic approach to In-beam Calibration Image the VLA 1.4 GHz primary beam (25 ); Identify compact sources. Verify compactness at higher frequencies with VLA. CONT: B2045-16 IPOL 8460.100 MHZ B2045-16.011.ICL001.7 CONT: B2045-16 IPOL 8460.100 MHZ B2045-16.008.ICL001.6-16 09 44.0-16 00 12.5 44.5 13.0 DECLINATION (J2000) 45.0 45.5 DECLINATION (J2000) 13.5 14.0 46.0 14.5 46.5 15.0 47.0 15.5 20 48 36.80 36.75 36.70 36.65 36.60 RIGHT ASCENSION (J2000) Cont peak flux = 1.0029E-02 JY/BEAM Levs = 3.000E-04 * (-4, -2, -1, 1, 2, 4, 8, 16, 32, 64, 128, 256) 20 48 49.65 49.60 49.55 49.50 49.45 RIGHT ASCENSION (J2000) Cont peak flux = 8.3376E-02 JY/BEAM Levs = 3.000E-04 * (-4, -2, -1, 1, 2, 4, 8, 16, 32, 64, 128, 256 ) 269 apparently compact sources imaged ( 4 / field).

A systematic approach to In-beam Calibration Image the VLA 1.4 GHz primary beam (25 ); Identify compact sources. Verify compactness at higher frequencies with VLA. Image with the VLBA. CONT: B2045-16 IPOL 1549.974 MHZ B2045-16.ICL001.1 CONT: B2045-16 IPOL 1549.974 MHZ B2045-16.1.ICL001.4 CONT: B2045-16 IPOL 1549.974 MHZ B2045-16.2.ICL001.1-16 16 44.49-16 09 45.49-16 00 13.97 44.50 45.50 13.98 44.51 45.51 13.99 DECLINATION (J2000) 44.52 44.53 44.54 44.55 DECLINATION (J2000) 45.52 45.53 45.54 45.55 DECLINATION (J2000) 14.00 14.01 14.02 14.03 44.56 45.56 14.04 44.57 45.57 14.05 44.58 45.58 14.06 20 48 35.609 35.608 35.607 35.606 35.605 35.604 35.603 RIGHT ASCENSION (J2000) Cont peak flux = 1.9113E-02 JY/BEAM Levs = 2.000E-03 * (-4, -2, -1, 1, 2, 4, 8, 16, 32, 64, 128, 256) 20 48 36.701 36.700 36.699 36.698 36.697 36.696 36.695 RIGHT ASCENSION (J2000) Cont peak flux = 2.0750E-02 JY/BEAM Levs = 3.000E-04 * (-4, -2, -1, 1, 2, 4, 8, 16, 32, 64, 128, 256) 20 48 49.574 49.573 49.572 49.571 49.570 49.569 49.568 RIGHT ASCENSION (J2000) Cont peak flux = 3.6290E-02 JY/BEAM Levs = 3.000E-03 * (-4, -2, -1, 1, 2, 4, 8, 16, 32, 64, 128, 256) 55 out 63 targets had 1 or more in-beam calibrator.

A systematic approach to In-beam Calibration Image the VLA 1.4 GHz primary beam (25 ); Identify compact sources. Verify compactness at higher frequencies with VLA. Image with the VLBA. Observe over 2 years: 8 epochs: {π max, π min }. 4 frequency bands, dual polarization, 256 Mb/s. High quality astrometry.

A systematic approach to Systematic Errors Bootstrap: infer uncertainties from the data itself.

A systematic approach to Systematic Errors Bootstrap: infer uncertainties from the data itself. 8 epochs 4 frequencies = 32 astrometric positions. Choose values with replacement. 32 32 combinations possible (but some are degenerate).

A systematic approach to Systematic Errors Bootstrap: infer uncertainties from the data itself. 8 epochs 4 frequencies = 32 astrometric positions. Choose values with replacement. 32 32 combinations possible (but some are degenerate). Explore 10, 000 fits...

A systematic approach to Systematic Errors Normal case: Bootstrap results for B0818 03

A systematic approach to Systematic Errors Worst case: Bootstrap results for J1713+0747

Southern hemisphere Long Baseline Array (Parkes, ATCA, Mopra, Tidbinbilla; +Hobart? +Ceduna?) Shorter baselines, poorer UV coverage, tougher calibration.

Southern hemisphere Long Baseline Array (Parkes, ATCA, Mopra, Tidbinbilla; +Hobart? +Ceduna?) Shorter baselines, poorer UV coverage, tougher calibration. Note ASKAP under construction in Western Australia.

Southern hemisphere Long Baseline Array (Parkes, ATCA, Mopra, Tidbinbilla; +Hobart? +Ceduna?) Shorter baselines, poorer UV coverage, tougher calibration. Fantastic parallax measurements by Deller et al. (2008, 2009). Relative Declination (mas) from -14 31 50.187139" 100 50 0-50 -100-150 Fitted pulsar path Fitted epoch point Position measurement -200-40 -20 0 20 40 60 80 Relative RA (mas) from 01 08 m 08.347016 s PSR J0108 1431 Relative Declination (mas) from -28 34 42.778813" 25 20 15 10 5 0-5 Fitted pulsar path Fitted epoch point Position measurement -10-60 -50-40 -30-20 -10 0 10 Relative RA (mas) from 06 30 m 49.404393 s PSR J0630 2834

Where do we stand? And what next?

Both quantity and quality Individual measurements can be extremely valuable. e.g., Astrometry on binary pulsars GR. e.g., Case studies outlined in this talk.

Both quantity and quality Individual measurements can be extremely valuable. e.g., Astrometry on binary pulsars GR. e.g., Case studies outlined in this talk. A large ensemble of measurements enables deeper insights. e.g., Velocities supernova core collapse. e.g., Electron density models.

Both quantity and quality Individual measurements can be extremely valuable. e.g., Astrometry on binary pulsars GR. e.g., Case studies outlined in this talk. A large ensemble of measurements enables deeper insights. e.g., Velocities supernova core collapse. e.g., Electron density models. Large samples test models, enable refinements (Chatterjee et al. 2009)

High Sensitivity VLBI Larger samples require higher sensitivities, better techniques. VLBA bandwidth expansion. High sensitivity arrays.

High Sensitivity VLBI Larger samples require higher sensitivities, better techniques. VLBA bandwidth expansion. High sensitivity arrays.

High Sensitivity VLBI Larger samples require higher sensitivities, better techniques. VLBA bandwidth expansion. High sensitivity arrays.... but larger telescopes smaller FoV; harder calibration; trickier phase referencing.

Technical Progress GPS Ionospheric calibration: capabilities improving.

Technical Progress GPS Ionospheric calibration: capabilities improving. Focal plane arrays: eliminate need to slew for phase referencing? Parkes testbed FPA; CSIRO July 2008

Final Thoughts and Future Directions Precision astrometry enables unique science. The origins, evolution, astrophysics, environments of NS. e.g., Constraints on supernova core collapse, NS kicks.

Final Thoughts and Future Directions Precision astrometry enables unique science. The origins, evolution, astrophysics, environments of NS. The importance of a consistent, systematic approach. Control of systematic errors essential. Larger field of view more inbeam sources. More sensitivity higher ν obs as well.

Final Thoughts and Future Directions Precision astrometry enables unique science. The origins, evolution, astrophysics, environments of NS. The importance of a consistent, systematic approach. Future instruments, technology, techniques: Ionospheric calibration: GPS. Focal plane arrays: vastly larger FOVs. SKA: mas resolution required for the µjy sky High precision radio astrometry.

Collaborators and Acknowledgements A long but incomplete list: Jim Cordes (Cornell), Bryan Gaensler (Sydney), Miller Goss, Walter Brisken, Adam Deller (NRAO), Wouter Vlemmings, Andrew Lyne, Michael Kramer (Jodrell), Joe Lazio (NRL), Zaven Arzoumanian (NASA GSFC), Stephen Thorsett (UCSC), Don Backer (UC Berkeley), Ed Fomalont, John Benson, Mark McKinnon (NRAO), David Kaplan (UCSB), David Helfand, Fernando Camilo (Columbia), and many others... Pulsar Astrometry: http://www.astro.cornell.edu/ shami/psrvlb/