Scuola%20nazionale%20de%20Astrofisica

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Scuola nazionale de Astrofisica Radio Pulsars 1
Pulsar Basics
Dick Manchester Australia Telescope National
Facility, CSIRO
Outline

• Rotating neutron stars, SN associations,
  Binaries, MSPs
• Pulse profiles, polarisation, beaming, RVM model
• Pulse fluctuations drifting, nulling, mode
  changing

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Basic References
Books

• Manchester Taylor 1977 Pulsars
• Lyne Smith 2005 Pulsar Astronomy
• Lorimer Kramer 2005 Handbook of Pulsar
  Astronomy

Review Articles

• Rickett 1990, ARAA - Scintillation
• Science, 23 April 2004 - Three articles NS,
  Isolated Pulsars, Binary Pulsars
• Living Reviews articles (http//relativity.livin
  greviews.org/Articles)
• Stairs 2003 GR and pulsar timing
• Lorimer 2005 Binary and MS pulsars
• Will, 2006 GR theory and experiment
• SKA science New Astron.Rev. 48 (2004)
• Cordes et al. Pulsars as tools
• Kramer et al. Strong-field tests of GR

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The Discovery of Pulsars
Jocelyn Bell and Tony Hewish Bonn, August 1980
The sound of a pulsar
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Spin-Powered Pulsars A Census

• Number of known pulsars 1765
• Number of millisecond pulsars 170
• Number of binary pulsars 131
• Number of AXPs 12
• Number of pulsars in globular clusters 99
• Number of extragalactic pulsars 20

Total known 129 in 24 clusters (Paulo Freires
web page)
Data from ATNF Pulsar Catalogue, V1.25
(www.atnf.csiro.au/research/pulsar/psrcat
Manchester et al. 2005)
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Pulsar Model

• Rotating neutron star
• Light cylinder RLC c/? 5 x 104 P(s) km
  
• ?Charge flow along open field lines
• Radio beam from magnetic pole (in most cases)
• High-energy emission from outer magnetosphere
• Rotation braked by reaction to magnetic-dipole
  radiation and/or charge acceleration ? -K
  ?-3
• Characteristic age ?c P/(2P)
• Surface dipole magnetic field Bs (PP)1/2

.
.
.
(Bennet Link)
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Pulsar Formation

• 30 young pulsars associated with SNR
• Core of red giant collapses when its mass
  exceeds Chandrasekhar Mass
• Energy release 3GM/5R2 3 x 1053 erg 0.1
  Mc2
• Kinetic energy of SNR 1051 erg 99 of grav.
  energy radiated as neutrinos and anti-neutrinos
• Asymmetry in neutrino ejection gives kick to NS
• Measured proper motions ltV2Dgt 211 km s-1
• ltV3Dgt 4ltV2Dgt/? 2ltV1Dgt for isotropic
  velocities

ESO-VLT
Guitar Nebula
PSR B222465
(Cordes et al. 2003)
(Hobbs et al. 2005)
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Neutron Stars

• Formed in Type II supernova explosion - core
  collapse of massive star
• Diameter 20 - 30 km
• Mass 1.4 Msun

(MT77)
(Stairs 2004)
(Lattimer Prakash 2004)
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.
P vs P
Galactic disk pulsars
.

• Most pulsars have P 10-15
• MSPs have P smaller by about 5 orders of
  magnitude
• Most MSPs are binary
• Only a few percent of normal pulsars are binary
• AXPs are slow X-ray pulsars with very strong
  fields - magnetars
• Some young pulsars are only detected at X-ray or
  ?-ray wavelengths

.
ATNF Pulsar Catalogue
(www.atnf.csiro.au/research/pulsar/psrcat)
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Pulsar Recycling

• Young pulsars live for 106 or 107 years
• MSPs have ?c 109 or 1010 years and most are
  binary
• Accretion from an evolving binary companion
  leads to

• Increased spin rate for NS - angular momentum
  transferred from orbit to NS
• Decreased Bs - mechanism not understood. Could
  be simple burial of field by accreted matter

.
.

• Minimum spin period Pmin (B9)6/7 (M/MEdd)-3/7
  
• Short-period MSPs from low-mass binary
  companions - long evolution time
• Recycling is very effective in globular clusters
  - more than half of all MSPs in globular
  clusters 22 in 47 Tucanae, 33 in Terzan 5
  (Ransom et al. 2005, Friere 2007)

• Old NS in core of cluster captured by low-mass
  stars and then recycled
• About 30 of MSPs are single - what has happened
  to companion?
• Blown away by relativistic wind from pulsar - ?
• Lost in 3-body encounter - only in core of
  globular cluster

47 Tucanae
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Pulsar Energetics
Spin-down Luminosity
Radio Luminosity
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Pulsar Electrodynamics

• For a typical pulsar, P 1s and P 10-15, Bs
  108 T or 1012 G.
• Typical electric field at the stellar surface E
  WRBs/c 109 V/cm
• Electrons reach ultra-relativistic energies in lt
  1 mm.
• Emit g-ray photons by curvature radiation. These
  have energy gtgt 1 MeV and hence decay into
  electron-positron pairs in strong B field.
• These in turn are accelerated to
  ultra-relativistic energies and in turn
  pair-produce, leading to a cascade of e/e-
  pairs.
• Relativistic pair-plasma flows out along open
  field lines.
• Instabilities lead to generation of radiation
  beams at radio to g-ray energies.

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Rotating neutron-star model magnetospheric gaps
W.B 0
Regions of particle acceleration!
Inner (polar cap) gap
Outer gaps
Cheng et al. (1986) Romani (2000)
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Coherent Radio Emission

• Source power is very large, but source area is
  very small
• Specific intensity is very large
• Pulse timescale gives limit on source size c?t
• Brightness temperature equivalent black-body
  temperature in Rayleigh-Jeans limit

Radio emission must be from coherent process!
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Frequency Dependence of Mean Pulse Profile

• Pulse width generally increases with decreasing
  frequency.
• Consistent with magnetic-pole model for pulse
  emission.
• Lower frequencies are emitted at higher
  altitudes.

Phillips Wolsczcan (1992)
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Magnetic-Pole Model for Emission Beam

• Emission beamed tangential to open field lines
• Radiation polarised with position angle
  determined by projected direction of magnetic
  field in (or near) emission region (Rotating
  Vector Model)

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Mean pulse shapes and polarisation
P.A.
Stokes I
Linear
Stokes V
Lyne Manchester (1988)
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Orthogonal-mode emission PSR B202028
V
P.A.
L
I
Stinebring et al. (1984)
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Mean pulse profile of PSR J0437-4715
P.A.
Stokes I

• Binary millisecond pulsar
• P 5.75 ms
• Pb 5.74 d

Linear
Stokes V

• Complex profile, at least seven components
• Complex PA variation, including orthogonal
  transition

I
L
V
Navarro et al. (1997)
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Wide Beams from Young and MS Pulsars

• Pulsed (non-thermal) X-ray and ?-ray profiles
  from young pulsars have wide double shape
• Emitted from field lines high in magnetosphere
  associated with a single magnetic pole
• Some young radio pulsars have a similar pulse
  profile, e.g. PSR B1259-63
• Class of young pulsars with very high (100)
  linear polarisation, e.g. Vela, PSR B0740-28
• Radio emission from high in pulsar
  magnetosphere?
• MSPs also have very wide profiles - also
  single-pole emission from high in magnetosphere?

Crab
(Ulmer et al. 1994)
PSR B1259-63
PSR B0740-28
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Other Examples
Vela
PSR B095008
PSR J0737-3039A
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Drifting subpulses and periodic fluctuations
Drifting subpulses
Periodic fluctuations
PULSE LONGITUDE
Taylor et al. (1975)
Backer (1973)
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Pulse Modulation

• Extensive survey of pulse modulation properties
  at Westerbork - 187 pulsars
• Observations at 1.4 GHz, 80 MHz bw
• Modulation indices, longitude-resolved and 2D
  fluctuation spectra computed
• 42 new cases of drifting subpulses

• At least 60 of all pulsars show evidence for
  drifting behaviour
• Coherent drifters have large characteristic
  age, but drifting seen over most of P - P diagram

.
(Weltevrede et al. 2006)
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Pulsar Nulling

• Parkes observations of 23 pulsars, mostly from
  PM survey
• Large null fractions (up to 96) - mostly
  long-period pulsars
• Nulls often associated with mode changing

(Wang et al. 2006)
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PSR B0826-34

• P 1.848 s, pulsed emission across whole of
  pulse period
• In null state 80 of time
• 5-6 drift bands across profile, variable drift
  rate with reversals
• Weak emission in null phase, 2 of on flux
  density
• Different pulse profile in null phase

Null is really a mode change.
On
Null
(Esamdin et al. 2005)
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PSR B193124 - An extreme nuller

• Quasi-periodic nulls on for 5-10 d, off for
  25-35 d
• Period derivative is 35 smaller when in null
  state!
• Implies cessation of braking by current with G-J
  density
• Direct observation of current responsible for
  observed pulses

(Kramer et al. 2006)
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Giant Pulses
Intense narrow pulses with a pulse energy many
times that of an average pulse - characterised by
a power-law distribution of pulse energies.
First observed in the Crab pulsar - discovered
through its giant pulses!
Crab Giant Pulses

• Arecibo observations at 5.5 GHz
• Bandwidth 0.5 GHz gives 2 ns resolution
• Flux density gt 1000 Jy
• implies Tb gt 1037 K!
• Highly variable polarisation
• Suggests emission from plasma turbulence on
  scales 1 m

(Hankins et al. 2003)
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Giant Pulses from Millisecond Pulsars
PSR B193721

• Giant pulses seen from several MSPs with high
  BLC
• Most also have pulsed non-thermal emission at
  X-ray energies
• Giant pulses occur at phase of X-ray emission

RXTE
PSR J02184232
BeppoSAX
GBT 850 MHz
Radio
Chandra 0.1-10kev
(Cusumano et al. 2003)
(Knight et al. 2006, Kuiper et al. 2004, Rutledge
et al. 2004)
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Transient Pulsed Radio Emission from a Magnetar

• AXP XTE J1810-197 - 2003 outburst in which X-ray
  luminosity increased by 100
• X-ray pulsations with P 5.54 s observed
• Detected as a radio source at VLA, increasing
  and variable flux density 5 - 10
  mJy at 1.4 GHz (Halpern et al. 2005)
• Within PM survey area, not detected in two obs.
  in 1997, 1998, S1.4 lt 0.4 mJy
• Observed in March 2006 at Parkes (Camilo et al.
  2006)

• Pulsar detected!
• S1.4 6 mJy
• Very unusual flat spectrum - individual pulses
  detected in GBT observations at 42 GHz!

Earlier unconfirmed detections (e.g. Malofeev et
al 2005) accounted for by transient and highly
variable nature of pulsed emission?
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End of Part 1