B - ICRA

Relativistic spin-precession
in binary pulsars
Michael Kramer
MPI für Radioastronomie
Jodrell Bank Centre for Astrophysics, University of Manchester
M.Kramer – MG12

Outline
• Introduction:
Theoretical expectations
Binary pulsars as labs for spin-precession
• The experiments
Observations, modelling, results
• Applications
GR and alternative theories
Astrophysical uses
• Summary & Conclusions
M.Kramer – MG12

Theoretical expectations
Due to the curvature of space-time the proper reference
frame of a freely falling object suffers “geodetic precession”
Experiments made in Solar System provide precise tests for this
effect and confirm it, e.g.,
- Lunar Laser Ranging
- Gyro-experiments, i.e. Gravity-Probe B
M.Kramer – MG12

Strong-field experiments
We would like to have also a gyroscope or spinning top in the presence
of strong gravitational fields…
We would like to use a massive, spinning test mass where we can
also infer and monitor the orientation of the spin direction
⇒ use binary radio pulsars
• In a binary pulsar system, geodetic precession leads to
“relativistic spin-orbit coupling”
• As a consequence, the pulsar spin precesses about the total angular
momentum, changing the relative orientation of the pulsar
M.Kramer – MG12

• …cosmic lighthouses
• …almost Black Holes:
Pulsars…
mass of ~1.4 Solar Mass within 20km
• …objects of extreme matter
– 10x nuclear density
– B ~ B cr = 4.4 x 10 13 Gauss
– Voltage drops ~ 10 12 volts
– F EM = 10 10-12 F gravity
– High-temperature superfluid superconductor
• …spinning with a wide range of periods:
J1748-2446ad
1.4 ms
Period
42,960 Rotations per Minute
7
J2144-3933
8.5 s
M.Kramer – MG12

Straw-man design of a pulsar
• rotation induces
electric quadrupole field
• charges pulled out of
surface, shielding force
• plasma fills surrounding
• co-rotation with pulsar
• light cylinder: v=R L Ω=c
• open and closed fieldlines
• coherent emission,T b >10 31 K
• MASER emission?
Pulse shape determined by 2-D cut through non-uniform 3D beam:
M.Kramer – MG12

Polarization: Signatures of Geometry
• Geometry is important to understand pulsar properties
• Pulsar emission is highly elliptically (mostly linearly) polarized
• Circular component not understood
• Linear component reflects B-field and geometry
• “Rotating-Vector-Model”
(Radhakrishnan & Cooke 1969)
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The life of pulsars: death & rebirth
Kramer & Stairs (2008)
Dead pulsars with a
companion can be spun-up
(“recycled”) to become
millisecond pulsars with
WD companion or perhaps
Double Neutron Stars
NASA
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Spin-Orbit coupling due to misaligned spins
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Geodetic Precession
• Relativistic Spin-Orbit Coupling
expected
• First prediction for observations
by Damour & Ruffini (1974)
• Precession rate expected in GR:
(e.g. Barker & O’Connell ‘75, Börner et al. ‘75, Hari Dass & Radhakrishnan ‘75)
5/
3
2π ⎞ 2 / 3 mc(
4mp
+ 3mc
) 1
−3
⎟ T�
, T = GM
4 / 3 2 � �
Pb 2(
mp
+ mc)
1−
e
p ⎛
Ω = ⎜
c
⎝ ⎠
What effects do we expect to observe?
M.Kramer – MG12

Geodetic Precession
• Relativistic Spin-Orbit Coupling
expected
• First prediction for observations
by Damour & Ruffini (1974)
M.Kramer – MG12

Geodetic Precession
• Relativistic Spin-Orbit Coupling
expected
• First prediction for observations
by Damour & Ruffini (1974)
Right ideas from the start:
• Changing angles = changing pulsed radiation
• Emission properties modulated with
precession frequency
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Effects of Geodetic Precession
• Firstly, pulsar may not always be visible
• Line-of-Sight will change
• Changes in pulse shape, width and polarization
M.Kramer – MG12

Effects of Geodetic Precession
Cutting the beam at different precession phases:
• Firstly, pulsar may not always be visible
• Line-of-Sight will change
• Changes in pulse shape, width and polarization
M.Kramer – MG12

Observations and Experiments
• For geodetic precession to be observed, we need binary system with
misalignment between pulsar spin and total angular momentum vector
• We require a system where last component was formed in an
asymmetric supernova explosion
P(ms) P b (d) x(lt-s) e Ω(º/yr)
J0737-3039 22.7/2770 0.10 1.42/1.51 0.09 4.8/5.1
B1534+12 37.9 0.42 3.73 0.27 0.5
J1518+4904 40.9 8.64 20.0 0.25 -
J1756-2251 28.5 0.32 2.76 0.18 0.76
DNS J1753-2240 95.1 13.63 18.1 0.30 -
J1811-1736 104.2 18.8 34.8 0.83 -
J1829+2456 41.0 1.18 7.24 0.14 0.08
J1906+0746 144.1 0.17 1.42 0.09 2.2 preecession
B1913+16 59.0 0.33 2.34 0.62 1.2 =
B2127+11C 30.5 0.34 2.52 0.68 1.9
PSR-WD J1141-6545 394.0 0.20 ?? 0.17 1.4 Red observed
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The first: PSR B1913+16
Discovered by Hulse & Taylor in 1974
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The pulse shape of PSR B1913+16
First studies by Weisberg, Romani & Taylor (1989):
Weisberg et al.’89
No conclusive result:
1981
• Amplitude was changing slowly
changing with time
• Expected change in width was
not detected!
• \
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The pulse shape of PSR B1913+16
First studies by Weisberg, Romani & Taylor (1989):
Kramer ‘98
Weisberg et al.’89
1995
1981
1.2%/yr
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The pulse shape of PSR B1913+16
First clear detection of geodetic precession (Kramer 1998):
Kramer (1998, 2000, 2002,2003)
Kramer (1998)
• Profile found to become narrower with time
• Prediction: pulsar will disappear in 2025!
• Simple four parameter model incl misalignment angle: SN explosion
• Derive beam map or make quantitative test…
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The first results…
Faith… Confirmation…
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Beam mapping
• Observations explained in simple bean model (Kramer 2000)
• High-sensitivity Arecibo observations suggest some deviation
(Weisberg & Taylor 2000, 2002; Clifton & Weisberg 2008):
Kramer (2000)
Basic idea: use slices through beam with time to reconstruct
the previously unknown 3D image of pulsar beam!
Clifton & Weisberg (2008)
M.Kramer – MG12

The second case: B1534+12
Smaller effect but first with polarization information
(Stairs et al. 2000, 2004):
• First time to measure changing geometry from polarization
• Combination of aberration and precession effect detected
• First attempt to derive quantitative test of precession rate
M.Kramer – MG12

The second case: B1534+12
Smaller effect but first with polarization information
(Stairs et al. 2000, 2004):
• First time to measure changing geometry from polarization
• Combination of aberration and precession effect detected
• First attempt to derive quantitative test of precession rate
M.Kramer – MG12

The third: PSR J1141-6545
• First non-DNS system: unusual system where young pulsar is in
orbit with old heavy white dwarf
• Relativistic 4.7-hr orbit, ideal for tests of alternative theories
of gravity (see Verbiest’s talk in EG6 session on Thursday!)
• Monitored by us since 2000, but also studied and first published
by Hotan et al. (2005):
Hotan et al. (2005)
M.Kramer – MG12

The third: PSR J1141-6545
• First non-DNS system: unusual system where young pulsar is in
orbit with old heavy white dwarf
• Relativistic 4.7-hr orbit, ideal for tests of alternative theories
of gravity (see Verbiest’s talk in EG6 session on Thursday!)
• Monitored by us since 2000, but also studied and first published
by Hotan et al. (2005)
• Rich behaviour in pulse shape, width and polarization (see
Manchester et al. to be submitted):
Manchester et al. (subm.)
Manchester et al. (subm.)
M.Kramer – MG12

The third: PSR J1141-6545
• New modeling (see Kramer & Wex 2009) uses previously unused
information about spin-axis provided by absolute position angle
• Requires careful calibration and RM measurements
(Manchester et al. to be submitted:)
Position Angle (deg)
Time
Precession Phase
Misalignment Angle
M.Kramer – MG12

The third: PSR J1141-6545
• New modeling (see Kramer & Wex 2009) uses previously unused
information about spin-axis provided by absolute position angle
• Requires careful calibration and RM measurements
(Manchester et al. to be submitted:)
• Self-consistent model that allows us to fit RVM to all epochs
(i.e. 930 data points to just 4 parameters):
Manchester et al. (subm.)
• First mapping of unrecycled pulsar beam pattern!
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The fourth: PSR J1906+0746
• Second most relativistic pulsar (Lorimer et al. 2006)
• Geodetic precession easily detected via interpulse component:
Lorimer et al. (2005)
• Unrivalled constraints from polarisation: excellent fit of
4-param’s Kramer & Wex (2009) model: χ 2 =1.21 for 632 D.o.F. !
Desvignes et al. (to be submitted)
Desvignes et al. (2008)
See talk by Gregory
Desvignes in EG6 on
Thursday!
M.Kramer – MG12

The best: PSR J0737-3039
PSR J0737-3039A/B discovered in April 2003:
first and only system with two active pulsars
Burgay et al. (2003), Lyne et al. (2004)
J0737-3039
McLaughlin et al. (2004)
• A young 2.77-s pulsar in a 2.4-hr
orbit with an old 22-ms pulsar.
• Orbital velocities of 1 Million km/h!
• Ideal lab for gravitational physics and
understanding pulsars and neutron stars.
M.Kramer – MG12

The Double Pulsar
Five(!) unique strong-field tests, represented in a single mass-mass plot:
Mass ratio & 6 PK parameters
⇔7-2 = 5 tests of GR!
Periastron
advance
More than in any system!
Gravitational
redshift
s
s
exp
obs
Shapiro
delay
Best strong-field test
= 1.
0000 ± 0.
0005
Kramer et al (2006), Breton et al. (2008)
Kramer et al. (2006)
See Rob Ferdman’s talk
in EG6 on Thursday
and public talk in evening!
Grav. wave emission
Mass ratio
(two orbits!)
Shapiro
delay
Spin-orbit
coupling
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Geodetic Precession in J0737-3039A
• Precession period of double pulsar only 71/74 years!
A B
Ferdman et al (2008)
Manchester et al. (2005)
Burgay et al. (2005)
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Sin i=0.99987(-48.+13)
A B
McLaughlin et al. (2004)
Eclipses of A
To Earth
20,000km
Orbital phase →
Peaks of emission not random!
Separated by P and P/2 of B
• Caused by synchrotron
absorption of plasma trapped
in B’s magnetosphere and
heated by A’s wind: see
Luytikov & Thompson (2005)
← lasting for ~27 sec
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Spin precession of B also seen in eclipse pattern:
Breton et al. (2008):
• Eclipse profile is changing
with time
• Pattern is changing due to
relativistic spin precession
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Relativistic Spin-Precession
• We can both explain the eclipse pattern and measure the precession
rate as a new test of general relativity (Breton et al 2008):
See Rene Breton’s talk
In EG6 on Thursday!
• Measured with 13% precistion and in agreement with GR’s
precession rate of 5.1 deg/yr
• Also, first unique constraint on alternative theories due to
measurement of theory-independent spin-precession parameter
M.Kramer – MG12

Theory-independent constraints
In a general class of theories, one can describe the SO-coupling
with a Lagrangian (see Damour & Taylor 1992):
Coupling function, different for different theories
In this framework, we write a general (average) precession rate
for pulsar B as:
with
Coupling constant
Strong-field modified grav. constant
M.Kramer – MG12

Theory-independent constraints
We can rewrite precession rate in terms of observables:
measured to be determined
Note that both X A and X B are simultaneous
measurable only in the Double Pulsar!
M.Kramer – MG12

Theory-independent constraints
We can rewrite precession rate in terms of observables:
measured to be determined
Note that both X A and X B are simultaneous
measurable only in the Double Pulsar!
We measure: whereas in GR:
M.Kramer – MG12

In other words, we have for the first time a measurement of the
coupling constant!
With
Theory-independent constraints
whereas in GR we expect a value of 2.
� This is the first time that we have a measurement of this strongfield
parameter. All theories of gravity must predict this value.
Unique Unique test test of of effacement effacement property property of of spinning spinning body! body!
M.Kramer – MG12

Applications of spin-orbit coupling
• Tests of theories of gravity
• Beam mapping and emission physics
• Core collapse supernovae and kick mechanisms:
- first such application by Wex et al. (2000) for PSR B1913+16:
- From geodetic precision
derive geometry
- Compute back in time
until last supernova
- Use conservation laws
(momentum etc.) to
constrain pre-supernova
system e.g. derive kick
amplitude and direction
Kick velocity
Polar angle of kick
M.Kramer – MG12

PDF
Applications of spin-orbit coupling
• Tests of theories of gravity
• Beam mapping and emission physics
• Core collapse supernovae and kick mechanisms:
- first such application by Wex et al. (2000) for PSR B1913+16
- see large amount of work by Kalogera group, e.g. Willems et al. ’04
- or our work on PSR J0737-3039B by Stairs et al. (2006)
Stairs et al. (2006)
J0737-3039
B1534+12
J0737-3039
B1534+12
⇒ Progenitor of B was light: 1.37-1.80 M � (95%)!
⇒ Different formation process? WD collapse?
J0737-3039
B1534+12
M.Kramer – MG12

Applications of spin-orbit coupling
• Tests of theories of gravity
• Beam mapping and emission physics
• Core collapse supernovae and kick mechanisms:
- first such application by Wex et al. (2000) for PSR B1913+16
- see large amount of work by Kalogera group, e.g. Willems et al. ’04
- or our work on PSR J0737-3039B by Stairs et al. (2006)
• Moment-of-inertia measurement and EoS:
Total periastron advance at 2PN level: Damour & Schaefer (1988)
3β
tot
k
2
0 =
1−
eT
1 0 0 S 0 S S 0β
S
[ ]
2 A A B B
+ f β − g β β − g β
1PN 2PN Spin A Spin B
2πc
1
β =
G P
Neutron star dependent S
2
p
I
m
Lattimer & Schutz (2005)
See Kramer & Wex ‘09
M.Kramer – MG12

Summary & Conclusions
• After first detection in PSR B1913+16, spin-orbit coupling has
been observed, modelled and used in a number of binary pulsars
• We observe all predicted effects like changes in pulse width,
shape, polarisation and overall visibility
• Finally, we are also doing quantitative tests with a first
confirmation of the effacement property of spinning bodies in
strong gravitational fields
• Besides tests of gravitational theories, we have a new tools for
astrophysics to study pulsar beams, the core collapse of massive
stars, the formation of neutron stars and eventually the
measurement of NS moment of inertia with constraints for the
Equation-of-State.
M.Kramer – MG12