Forefront of neutron star science Forefront of neutron star science


НазваForefront of neutron star science Forefront of neutron star science
Дата конвертації06.06.2013
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Forefront of neutron star science

  • Forefront of neutron star science

  • Precision astrometry using the VLBA

  • Bowshocks and jets

  • Pulsar velocities:

      • Bimodality
      • Kick mechanisms: tie-ins to cosmology?
  • ALFA: A massive pulsar survey at Arecibo

  • SKA: toward a full Galactic census of pulsars


Pulsars…

  • embody physics of the EXTREME

    • surface speed ~0.1c
    • 10x nuclear density in center
    • some have B > Bq = 4.4 x 1013 G
    • Voltage drops ~ 1012 volts
    • FEM = 109Fg = 109 x 1011FgEarth
    • Tsurf ~ million K
  • …relativistic plasma physics in action

  • …probes of turbulent and magnetized ISM

  • …precision tools, e.g.

  • - Period of B1937+21:

  • P = 0.00155780649243270.0000000000000004 s

  • - Orbital eccentricity of J1012+5307: e<0.0000008



Pulsar Populations: P – Pdot diagram

  • Canonical

      • P~ 20ms – 5s
      • B ~ 1012±1 G
  • Millisecond pulsars (MSPs)

      • P ~ 1.5 – 20ms
      • B ~ 108 – 109 ms
  • High field

      • P ~ 5 – 8 s
      • B ~ few x 1013 G
  • Braking index n:

      • Pdot  P2-n, n=3 magnetic dipole radiation
  • Death line

  • Strong selection effects



Forefronts in NS Science

  • Understanding NS populations and their physical differences

      • Radio pulsars and their progenitors
      • Magnetars
      • Radio quiet/Gamma-ray loud objects
      • Branching ratios in supernovae
  • The physics of NS runaway velocities

  • Are “neutron stars” neutron stars?



Forefronts in NS Science

  • Finding compact relativistic binary pulsars for use as laboratories

      • Gravity
      • Relativistic plasma physics in strong B
  • Finding spin-stable MSPs for use as gravitational wave detectors ( ~ light years)

      • h ~ TOA T-1 (T = data span length)
  • Complete surveys of the transient radio sky

      • pulsars as prototype coherent radio emission


First Double Pulsar: J0737-3939



Velocity Distribution

  • Gunn and Ostriker 1970

  • Early estimates using interstellar scintillation measurements of radio pulsars

  • Millisecond pulsars:

      • High velocity by stellar standards
      • Slow by comparison to high-B objects (V~100 km s-1)
  • Canonical pulsars:

      • ~ 400 km s-1 (Lyne and Lorimer 1994)
      • Bimodal PDF (Cordes and Chernoff 1998)


Bow Shocks







Bow Shocks



Bow Shocks



NS Bow Shock?

  • G70.7+1.2

      • A cometary HII region? (Bally et al. 1989)
      • A Be-NS binary? (Kulkarni et al. 1992)
      • Bow shock contours seen in narrowband IR images and in radio (VLA)
      • Chandra image indicates presence of compact star as cause of bowshock




Uncertainties in the Velocity PDF

  • Pulsar survey selection effects:

      • Beaming
      • Period dependence of pulsar luminosity
      • Frequency and period dependent selection effects
        • ISM propagation (dispersion, scattering)
  • Velocity selection in volume limited pulsar surveys

      • Low-Galactic latitude surveys miss high-V pulsars born in the Galactic plane
  • CC98 not corrected for selection effects, but high-V component ~ x5 too low

  • ACC02 corrected for selection effects but uses distance estimates with large errors





VLBI / VLBA



Pulsar astrometry Science Case (Brisken et al. 2002, Chatterjee et al. 2001-2004)

  • Pulsar Origins:

      • SNR associations
      • NS birth sites in stellar clusters / OB associations
      • True ages
  • Astrophysics:

      • NS atmospheres, cooling curves etc. need absolute distances
  • Evolution:

      • NS distribution and population velocities
  • Environments:

      • Galactic electron density
      • local ISM


In-Beam calibration

  • In-beam calibration:

    • referencing to a source within the primary telescope beam
      • 20 arcmin at 1.4 GHz on the VLBA antennas
      • less for e.g. AO and GBT and at higher frequency


Parallax / Proper Motion

  • B1929+10

    • both at 1.4 and 5 GHz
  • D = 361+10-8 pc

  • V = 177+4-5 km/s

  • Chatterjee et al. 2004



Current Status of Large Astrometry Program Using the VLBA

  • 26 pulsars observed at 8 epochs over 2 years

  • 2/3 use in-beam calibration

  • Expect 20 new parallaxes “soon”

  • Another set of pulsars is now being observed



Ongoing 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, Vlemmings, 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



Separated at Birth

  • B2021+51 and B2020+28 originate from same binary

  • Disrupted in second SN explosion

    • 1.9 Myr ago
    • c.f. spindown ages of 2.88 and 2.75 Myr
  • Birth Location: the Cygnus Superbubble

  • Birth velocities:

    • 200 km/s kick
      • 150 km/s (B2021)
      • 500 km/s (B2020)
  • Second created pulsar (B2020)

    • P0 ~ 200 ms




B1508+55



NE2001: Galactic Distribution of Free Electrons + Fluctuations



Local ISM Components of NE2001



Pulsar Velocity Distribution Using only Parallax Distances

  • Likelihood analysis for birth parameters:

    • using pulsars with accurate astrometry
    • 1 component model
      • V1 = 175 km/s
      • hz = 0.2 kpc
    • 2 component model
      • V1 = 86 km/s
      • V2 = 296 km/s
      • hz = 0.16 kpc


Bias Against High-V in current sample

  • (,) and age<25 Myr

      • only 14 pulsars
  • Simulations show our distribution is consistent with selection effects on pulsar population with

      • V1 = 90 km/s
      • V2 = 500 km/s
      • (Arzoumanian, Cordes & Chernoff 2002)
  • Volume limited sample biases against high V



Understanding the Velocity Distribution

  • Two components suggest  2 processes

      • E.g. orbital disruption + asymmetric supernovae
  • But two independent processes will not produce a bimodal PDF

      • Convolution  unimodal PDF
  • Need “kick” processes to be selective

  • Extreme case: Bombaci and Popov (2004):

        • Low V NS are hadronic
        • High V “NS” are quark stars that undergo two kicks (including one corresponding to phase transition to quark matter)


Pulsar Jets

  • Magnetospheric Jets

      • Along spin axis 
      • Nearly ║ to V
      • 0.1 to 1 pc in length


Pulsar Jets

  • Guitar Nebula Jet

      • Chandra 50 ksec ACIS obs
      • Misaligned from Guitar axis  proper motion direction


Pulsar Jets

  • Guitar Nebula Jet

      • Chandra 50 ksec ACIS obs
      • Misaligned from Guitar axis  proper motion direction
      • Jet luminosity is much larger fraction of Edot than in Crab and Vela pulsars
      • One-sided = two-sided + relativistic beaming?
      • Jet is straight for ~1pc
      • Consistent with synchrotron energy losses,  ~0.3c and jet within 30o of LOS
  • Explanation: magnetic reconnection in bow-shock nose

  • Cordes et al. 2005 (in prep)



Simulated Bow Shocks



Pulsar Jets

  • J2124-3358

      • MSP: P = 4.93s
      • B = 3.2x108 G
      • s = 3.8 Gyr
  • Probably a magnetospheric jet

      • Bent by the shocked ISM flow
  • Chatterjee et al. in preparation



Pulsar Kicks



Evidence for NS Kicks

  • Large NS Velocities (>> progenitors’ velocities ~ 30 km/s):





Clues about Kicks

  • Bimodality of the net velocity distribution

      • Includes combined effects of orbital disruption and natal kicks
  • The proper motion is nearly aligned with jets seen in the Crab and Vela pulsars

      • + a few other objects
      • common or chance?
      • Intrinsic to the kick mechanism or imposed by rotation? (Spruit & Phinney 1998; Lai et al. 2001)










Neutrino - Magnetic Field Driven Kicks





Electromagnetic Radiation Driven Kick (Boost)



Conditions for spin-kick alignment:





Toward a Galactic Census of Radio Pulsars

  • The first 30 years of pulsars:

      • ~ 700 radio pulsars
      • ~ 1% binaries
  • Parkes Multibeam Survey 1997-2004:

  • ~ 800 new pulsars

  • + Other surveys:

  • ~ 100 MSPs

  • 6 relativistic binary pulsars (NS-NS)

  • No PSR-BH binary (yet)

  • c.f. ~105 active radio pulsars (20% beamed to us)



Why more pulsars?









ALFA Galactic Plane Survey

  • Survey Galactic Plane

        • |b| < 5o  = 32o-77o and  = 168o-214o
        • 300 s / sky position (~30s needed to match PMB sensitivity)
        • Greater sensitivity to MSPs (narrower frequency channels)
        • 2000 hr telescope time over a 3-5 year period
  • 103 new pulsars

        • Reach edge of Galactic population for much of luminosity function
        • High sensitivity to millisecond pulsars and binary pulsars
        • Dmax = 2 to 3 times greater than for Parkes MB
  • Sensitivity to transient sources

  • Data management:

        • Keep all raw data (~ 1 Petabyte after 5 years) at the Cornell Theory Center Database of raw data, data products, end products
        • Web based tools for Linux-Windows interface (mysql  ServerSql)
        • VO linkage (in future)






The First ALFA Pulsar









Data Flow

  • Raw data obtained at Arecibo

  • Local processing at Arecibo

      • Quality control
      • Targeted scientific processing
  • Transport of raw data to processing centers (Cornell + 5 other institutions) via disk packs

  • Cornell Theory Center role:

      • Initial search analysis (by Cornell researchers)
      • Incorporation of data/products from all processing sites into database plus access tools (joint Astronomy/CS effort)
      • Provide capabilities for meta-analysis of search output for candidate identification; used by Pulsar Consortium Institutions.
      • Long-term archival of raw data and data products for future processing, cross-correlation with future instruments (ground and space-based). Used by the general astronomical community. (National Virtual Observatory)


The Square Kilometer Array



The Collecting Area Plateau In Radio Astronomy





ALFA pulsar surveys will be the deepest surveys of the Galaxy until the SKA is built:



Example of the SKA as a Pulsar-Search Machine

  • ~104 pulsar detections with the SKA (assuming all-sky capability)

  • rare NS-NS, NS-BH binaries for probing strong-field gravity

  • millisecond pulsars < 1.5 ms

  • MSPs suitable for gravitational wave detection

  • Galactic tomography of electron density and magnetic field

  • Spiral-arm definition



Cosmological Gravitational Wave Background



SKA Specifications Summary for Fundamental Physics from Pulsars





Axes of Discovery for the SKA







The brightest pulses in the Universe





International SKA Project

  • Active participation by US, Canada, China, India, Australia, Europe (esp. UK, Netherlands, Italy), South Africa

  • Timeline for milestones: now to 2020

      • Site selection 2006
      • Technical concept 2008
      • Demonstrator array 2009 – 2012?
      • Full array 2015 – 2020?
  • International SKA Steering Committee

      • 21 members
      • 7 US members reflects targeted 33% funding of SKA by the US


US SKA Consortium Chair: Yervant Terzian (Cornell) Vice Chair: Jack Welch (UCB)



Architectures for the SKA





Technology Development for the LNSD Concept by the USSKAC

  • Allen Telescope Array

  • EVLA

  • Low frequency arrays (LWA, MWA)

  • NSF/ATI funding (2002-2005)

  • Technology Development Project

      • Managed by NAIC for the USSKAC
      • Submitted to NSF for $32M 2004 March
      • Panel review 2004 October
      • Funding Post Senior Rev.






Summary

  • Pulsars continue to live up to their utility as physics laboratories

  • The best is yet to come with a full Galactic census for neutron stars

  • Arecibo/ALFA will provide ~ 1000 new NS

  • SKA will finish the Galactic census and begin extragalactic searches

  • The SKA will transform radio science and astrophysics in other important ways



Extra Slides



Bow Shocks



Interferometry / Astrometry

  • VLB arrays result in incomplete sampling of the U-V plane

  • Imaging possible using self-calibration and deconvolution (“CLEAN”)

    • self-calibration destroys absolute positional information
    • astrometry needs phase-referencing


Phase referencing

  • Alternating scans on extra-galactic reference source with known position

    • solves for atmospheric effects
      • ionosphere  -1
      • troposphere  +1
  • Pulsar flux  - , =1.5 to 2.5

    • phase referencing at 1.4 GHz compromise
    • positional scatter at 5 GHz lower
  • Making phase connections at 1.4 GHz requires:

    • 2-3 minute alternating scans over less than 4-5°


Pulsar gating



Astrometry results



Pulsar astrometry Science applications

  • Pulsar Origins:

      • SNR associations
      • NS birth sites in stellar clusters / OB associations
      • True ages


SNR association

  • PSR B0656+14

    • originally thought to be at approx. 800 pc while SNR at 300 pc
    • VLBA pulsar parallax = 290 pc


Pulsar astrometry Science applications

  • Pulsar Origins:

      • SNR associations
      • NS birth sites in stellar clusters / OB associations
      • True ages
  • Astrophysics:

      • NS atmospheres, cooling curves etc. need absolute distances


NS Cooling models



Pulsar astrometry Science applications

  • Pulsar Origins:

      • SNR associations
      • NS birth sites in stellar clusters / OB associations
      • True ages
  • Astrophysics:

      • NS atmospheres, cooling curves etc. need absolute distances
  • Evolution:

      • NS distribution and population velocities


Spin-Kick Connection



Spin-velocity alignment in Vela and Crab





Arecibo and the RI Project

  • Galactic Plane Survey:

    • 2000 hr @ 112 MB s-1 = 806 TB
      • Telescope time: ~$2k/hr
      • 3-5 years to acquire data (modulo telescope demand, interference)
    • Reobservations of candidate signals
    • Iterative process of acquiring raw data, data reduction, reobservations, cross correlations with other databases, reprocessing with newer algorithms
    • RI project:
      • establishment of Cornell processing center
      • development of database and meta-analysis tools
      • Collaboration between Astronomy and CS Departments + CTC
      • provision for access of data and tools by Pulsar Consortium and wider community of researchers longer term


Precursor Survey

  • 57 hr (37 inner Galaxy, 20 anticenter) Aug-Oct 2004

      • ~20 deg2 each region (different dwell times)
  • WAPPs: 7 x 100MHz/256 ch x 64 μs dumps

  • Real-time analysis:

      • Uses ASP = Arecibo Signal Processor (cluster: UCB, UBC, Princeton +)
      • Degraded t-f resolutions (for throughput)
      • 11 new pulsars
          • 10 via standard dedispersion/periodicity search
          • 1 via single pulse (transient detection)
      • 28 known pulsars detected
      • All known pulsars within FHWM of ALFA beams detected
  • Off-line analysis:

      • full t-f resolution
      • expect to double the search volume of the real-time analysis
      • In progress
  • Paper draft in preparation



PALFA Consortium

  • 33 current members, including students

  • Active involvement in survey planning, development of software package, development of database tools

  • 50% took part (on site) in the precursor survey + others off site

  • 2 undergraduate summer students

  • Data processing of full survey data to be done at member institution sites (Cornell, Jodrell, McGill, NRAO, NRL?, UBC)

  • Data products shipped to Cornell Theory Center for meta analysis and long-term archival



Full Survey Proposal

  • Submitted 2004 Oct 1 by PALFA Consortium

      • Requests 420 hours for inner Galaxy + anticenter
      • One new pulsar per 1.5 hr of on-sky telescope time
      • Approved by Skeptical Review panel
      • Observations start mid-March 2005
  • Spectrometers:

      • WAPPs initially (100 MHz bw, 256 channels)
      • New PALFA spectrometer
          • FPGA based polyphase filter bank
          • 300 MHz bandwidth, >1024 channels
          • Availability: 2005 TBD


PALFA Surveys

  • Most demanding of the ALFA surveys in data volume

      • ~ 100 MB/s to disk
      • ~ 1 PB for entire survey (3-5 yr @ 6-10% duty cycle)
  • Requires coarsely parallel processing of raw data in discrete, local data chunks

      • processing time ~ 50-200x data acquisition time on single processor (Intel 2.5 GHz 512k cache with 1GB ram)
      • depends on data set details, algorithms, code
      • distributed initial processing (Cornell + 5 sites)
  • Requires meta-analysis of data products of the initial analysis enabled by Cornell database and algorithms for datamining



Arecibo and the RI Project

  • Galactic Plane Survey:

    • 2000 hr @ 112 MB s-1 = 806 TB
      • Telescope time: ~$2k/hr
      • 3-5 years to acquire data (modulo telescope demand, interference)
    • Reobservations of candidate signals
    • Iterative process of acquiring raw data, data reduction, reobservations, cross correlations with other databases, reprocessing with newer algorithms
    • RI project:
      • establishment of Cornell processing center
      • development of database and meta-analysis tools
      • Collaboration between Astronomy and CS Departments + CTC
      • provision for access of data and tools by Pulsar Consortium and wider community of researchers longer term


Why at Cornell?

  • National Astronomy and Ionosphere Center

    • Cornell operates the Arecibo Observatory under a cooperative agreement with the NSF
    • ALFA surveys are legacy activities whose success NAIC wishes to oversee, including
      • Data acquisition and processing
      • Explicit catalogs of sources disseminated to the astrophysical community
      • Long-term archiving for synergistic activities with future surveys
  • Department of Astronomy

    • Cornell faculty are directly involved with management, operations, and usage of Arecibo, including ALFA surveys
  • Department of Computer Science

    • Provides expertise in database design and data mining tools
    • Will make use of Arecibo data for datamining algorithm research
  • Cornell Theory Center

    • CTC’s mission is to support research groups and centers at Cornell
    • Can provide stable infrastructure and expertise needed for long-term archiving and for providing analysis tools in a high-performance computing environment


PALFA Issues

  • Data transport: disk pack failures

  • Proprietary period for raw data not settled

  • Paper authorship discussed but not yet settled apart from agreement on rotating first authorship

  • New PALFA members: by proposal to the Consortium executive committee (including thesis work)

  • Public relations for AO, NAIC and PALFA

      • Sorely needed for promoting NAIC (NSF Senior Review)


Commensal Observing

  • PALFA pointings

      • w/ SETI, EALFA, GALFA piggyback
  • EALFA pointings

      • w/ PALFA piggyback
  • Separate spectrometers needed

      • WAPPs (NAIC)
      • GALFA (UCB)
      • PALFA (NAIC/UCB)
      • EALFA (NAIC/UCB)
      • SETI (UCB)


International SKA timeline



The SKA Science Case

  • Special issue of New Astronomy, Carilli & Rawlings, eds.

  • Key science areas developed through a 2 year process of the International Science Advisory Committee

  • Builds upon work in the 1990s:

  • the hydrogen telescope (L* galaxies at z=1  SK)

  • SKA science book (Taylor & Braun)

  • pdf files available at: www.skatelescope.org



Example of the SKA as a Dark-Energy Machine

  • Contours (±1σ) for determination of the dark-energy equation of state parameter w=P/,

  • w(z) = w0 + w1z,

  • for SKA surveys and SNAP surveys

  • SKA ~ 108 - 109 galaxies



The 6th Key Science Area: Exploration of the Unknown

  • Today’s hot new issues are tomorrow’s old issues.

  • The excitement of the SKA will not be just the old questions it will answer but in the new questions it will raise.

  • We build telescopes for … discovery and understanding. What is the right mix?







Technology Development Project for the Square Kilometer Array





The Role of NAIC

  • Managing the NSF-funded TDP

  • Antenna optics and optimization (German Cortes)

  • AO as a testbed for wideband feeds and receivers developed for the SKA (FPAs)

  • ALFA surveys + data management as a model for SKA data management

  • NAIC as a gateway organization to low-frequency arrays in the southern hemisphere



Challenges in the US

  • Funding, funding, funding

  • Balancing SKA development in universities with development in NAIC, NRAO

  • Identify commonality with other array projects (ALMA, ATA, EVLA, LWA, MWA)

  • Dollars: NSF funding of radio facilities needs to be understood in an overall coherent plan for cm/m radio astronomy in the wider astrophysical context

  • Under development: a whitepaper that lays out a coherent plan of this type



Array Planning Group for cm/m

  • Motivation

    • Too many projects chasing too few NSF $$
    • Lack of coherent long-term plan
    • Desire to present coherent scenario/suggestion to RMSPG, the NSF, and the wider community
  • Approach

    • Convene group with representatives of most major upcoming/proposed cm/m projects
    • Produce whitepaper outlining science goals and a scenario to achieve them
      • Use whitepaper as stimulus for community discussion


Group Membership

  • Leo Blitz, UC Berkeley (Allen Telescope Array)

  • Jim Cordes, Cornell (PI of SKA TDP)

  • Namir Kassim, NRL (Long Wavelength Array)

  • Colin Lonsdale, Haystack-MIT (Mileura Widefield Array)

  • Rick Perley, NRAO (EVLA-2 PI)

  • Tony Readhead, Caltech (At-large, SKA)

  • Jim Ulvestad, NRAO





Pulsar Kicks







Kick Mechanisms

  • Rocket effects:

  • Hydrodynamically driven kicks

      • Asymmetric explosion
      • Fast: seconds
  • Neutrino-magnetic field driven kicks

      • Asymmetric neutrino emission
      • Fast: seconds
  • Electromagnetic radiation driven kicks

      • Asymmetric magnetic dipole radiation
      • Slow: spindown time scale ~ months for Pspin,0 ~ 1 ms


Pre-collapse Asymmetry



Dynamical Effects of Magnetic Fields



Neutron Star Kick Mechanisms



Initial Spin of Neutron Stars (Observations)





Initial Spin of Neutron Stars (Theory)



Early Spindown of Neutron Star



PWN Torus of PSR J0538+2817 in SNR S147





Summary



Black Hole Kicks





Black Hole Kicks



PALFA as Precursor to SKA Surveys

  • PALFA surveys will provide a comprehensive search of Arecibo’s Galactic sectors, the deepest until SKA

  • PALFA data management serves as model for large-scale SKA surveys

  • SKA will provide a full Galactic census of pulsars (~104)

  • RFI mitigation and generalized transient analyses in the t-f plane



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