Michael Kramer

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Was Einstein right?The Double Pulsar as a unique
testbed for strong-field gravity

• Michael Kramer
• Fermilab 15 December 2004

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Outline
Introduction

• Pulsar properties
• Binary pulsars as gravity labs

The Double Pulsar

• Discovery of A and B
• A unique testbed for GR

The Future
3
Outline
Introduction

• Pulsar properties
• Binary pulsars as gravity labs

The Double Pulsar

• Discovery of A and B
• A unique testbed for GR

The Future
4
The Discovery

• Jocelyn Bell
• Tony Hewish
• discover a periodic
• extra-terrestrial
• signal of 1.337 s at
• position
• RA 191936
• DEC 214716

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Pulsars Neutronstars
born in Supernova-explosions e.g. Crab pulsar
Golden Shearer
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Pulsars

• almost Black Holes
• objects of extreme matter
• 10x nuclear density
• B Bq 4.4 x 1013 Gauss
• Voltage drops 1012 volts
• FEM 109Fg 1011FgEarth
• High-temperature superfluid superconductor
• relativistic plasma physics in action
• probes of turbulent and magnetized ISM
• precision tools

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Pulsars Cosmic Lighthouses
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spinning fastvery fast!
typically once per second, but spanning four
orders of magnitude
Crab 33 ms
B193721 1.5 ms
J2144-3933 8.5 s
Period
Vela 89 ms
38,400
Rotations per Minute
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Single pulses are quite different
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Pulse structure is intrinsic and broadband
Longitude (deg)
Kramer et al. 2003c
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but average profiles are stable!
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but average profiles are stable!
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Pulse Structure Hollow Cone Model
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Pulse Structure Hollow Cone with Core
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The pulsar emission process
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Straw-man design of a pulsar model
D.Page
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The life of pulsars
Pulsars radiate
Energy must come from somewhere!
Taken from rotational energy
Measure change in spin frequency or period!
Pulsars slow down!
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The life of pulsars
P-Pdot diagram
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The life of pulsars
P-Pdot diagram
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Science with Pulsars
Pulsars are very useful tools in many areas
For instance

• Relativistic gravity
• High precision astrometry
• Cosmology
• Solid state physics under extreme conditions
• Population stellar and binary evolution,
  Supernovae
• Plasma physics and electrodynamics
• Galactic probes Interstellar medium
• Magnetic field
• Star formation history
• Dynamics

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The Art of Pulsar Timing
High precision possible, e.g. period of
B193721 P 0.0015578064924327?0.000000000000000
4 s

• Measuring arrival times
• Time transfer to TT using GPS
• Transfer to solar system barycentre
• Comparison to timing model
• Identify deviations

• Pulsar/Telescope/Earth position
• Pulsar spin down
• Binary motion
• Relativistic effects

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Timing model

• Measure time of arrival (TOA)
• Refer TOA (local time) to time
• of emission in co-moving frame
• of pulsar

Roemer Delay
Rel.effects in Solar system
Effects in binary system
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Timing Parameters

• Spin parameters
• Astrometric parameters position, proper motion,
  parallax

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Binary pulsars as gravity labs

• 5 Keplerian-parameters
• Pb, ap, e, ?, T0

to order (v/c)2 1PN
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Binary pulsars as gravity labs

• Another example PK parameter
• Orbital decay due to gravitational wave
  emission

• Orbit shrinks by 1cm/day
• Evidence for gravitational waves!

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Binary pulsars as gravity labs mass-mass plot
Elegant method to test any theory of gravity
(Damour Taylor 92)
All PK parameter can be written as function
of only observed Keplerian and the masses of
pulsar and companion
Fail!
Pass!
f, g depend on theory!
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Binary pulsars as gravity labs mass-mass plot
B191316 (Weisberg Taylor 03)
non-radiative test
radiative test
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Outline
Introduction

• Pulsar properties
• Binary pulsars as gravity labs

The Double Pulsar

• Discovery of A and B
• A unique testbed for GR

The Future
29
Outline
Introduction

• Pulsar properties
• Binary pulsars as gravity labs

The Double Pulsar

• Discovery of A and B
• A unique testbed for GR

The Future
30
Parkes Multibeam Survey
lead by Jodrell Bank in collaboration
with ATNF, Bologna, UBC et al.
75 by JBO

• Most sensitive most successful
• More than 700 discoveries
• Still counting
• Lots of exciting systems

Manchester et al. 2001, Morris et al. 2002 Kramer
et al. 2003, Hobbs et al. 2004, Faulkner et al.
2004
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Discovery of A
PSR J0737-3039 discovered in April 2003 in an
PKSMB extension the Parkes High-LatitudePulsar
Survey (Burgay et al., Nature, 2003)

• Selected area b lt 60, 220 lt l lt 260
• total of 6456 pointings each lasting 4 min.

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Discovery of A
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Discovery of A

• Observations showed that the orbit is very tight
  (2.4 hrs) and eccentric (e 0.088) with orbital
  velocities
• of 300 km/s!

• Orbital parameters suggested that the companion
  to 22-ms pulsar is probably another neutron star

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Discovery of B
In October 2004 the system became sensational
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Discovery of B
In October 2004 the system became sensational
A holy grail was discovered - the first double
pulsar!
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Discovery of B
Discovery of an additional 2.77-sec periodicity!
(Lyne et al., Science, 2004)
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Basic parameters
B
A
P P Char.age Bsurf RLC BLC dE/dt Mean Vorb
22.7 ms 1.7 x 10-18 200 Myr 6 x 109 G 1,080 km 5
x 103 G 6 x 1033 erg s-1 301 km s-1
2.77 s 0.82 x 10-15 50 Myr 1.6 x 1012 G 1.32 x
105 km 0.7 G 1.6 x 1030 erg s-1 323 km s-1
.
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System Configuration

• Wind energy density at B light cylinder
• A 2.1 erg cm-3 B 0.024 erg
  cm-3
• Therefore, A wind will penetrate B
  magnetosphere.
• Approximate pressure balance with Bs magnetic
  field
• at r 0.45 RLC. Will vary with spin and
  orbital phase.

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Orbital modulation of B emission
Two bright intervals near inferior conjunction
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Orbital modulation of B emission
50cm (680 MHz)
10cm (3 GHz)
Lyne et al. (2004)
Lyne et al. (2004)
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Direct modulation of Bs emission by A
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Eclipses of A
Lyne et al. (2004)
10cm
20cm

• At superior conjunction
• Lasting for 27 sec
• Deepest just AFTER
• superior conjunction

50cm
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Eclipses of A
At 88o inclination, LOS to A passes 30,000 km
from B!
McLaughlin et al. (2004b)
We can see the rotation of B!
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Magnetospheric interaction

• Strong B emission only when polar field lines
  open in A
• wind direction.
• Expect changes in modulation pattern as rotation
  axis
• precesses.
• Unpulsed continuum
• emission detected
• (4 mJy _at_ 20cm)
• CHANDRA/XMM
• detection at X-rays

McLaughlin et al., 2004c
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Boost for gravitational wave hunters

• Neutronstars merge after only 85 Myr due to
• gravitational wave emission!

Since system is accelerated merges
soon is close not very luminous
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GR with the double pulsarThe most relativistic
system ever!
Huge relativistic precession of the orbit
periastron advance of 17 deg/yr!

• Also, orbital decay and huge rel.spin-orbit
  coupling!

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Spin-Orbit Coupling due to misaligned spins
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Geodetic Precession

• Relativistic Spin-Orbit Coupling
• First prediction for binary pulsar
• by Damour Ruffini (1974)
• Precession rate expected in GR
• (e.g. Barker OConnell 1975, Börner et al.
  1975)

(Again, only dependant on masses and Keplerian
parms)
What effects do we expect to observe?
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Effects of Geodetic Precession
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Effects of Geodetic Precession

• Pulse shape changes!

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Effects of Geodetic Precession
Kramer (1998, 2002,2003)
B191316

• Pulse shape changes (seen in B191316, B153412,
  J1141-6545!!!)

• B191316 (Period 300 yr) will disappear 2025!
  (Kramer 1998)

• Total precession period of J0737-3039 only 75
  years!!

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Geodetic Precession in J0737-3039
not yet!
Manchester et al. (submitted)

• Geometry still unconstrained
• Jenet Ransom (2004) model
• ruled out

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Detection of Shapiro delay
Pulses of A are delayed when propagating through
curved space-time near B
Compare to scintillation measurements
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Scintillation measurements
Intensity variation due to ISM depending on
relative vel.
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Scintillation measurements
Even better at conjuction they see the same ISM
? correlation of scintillation properties
Refraction of A in B's magnetosphere?
Coles et al.(in press)
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Tests of GR
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Tests of GR
Mass function A
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Tests of GR
Mass function B
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Tests of GR
Mass ratio
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Tests of GR
Periastron advance
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Tests of GR
Grav. Redshift 2nd order Doppler
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Tests of GR
Shapiro s
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Tests of GR
Shapiro r
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Tests of GR
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Tests of GR
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Tests of GR
December 2003 (Lyne et al. 2004)
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Tests of GR
July 2004

• Mass ratio 5 PK parameters
• 6-2 4 potential tests!
• More than in any system!

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Tests of GR
July 2004
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Tests of GR
July 2004
Now
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Tests of GR
July 2004
Kramer et al. in prep.
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Tests of GR
July 2004
Kramer et al. in prep.
MB1.249(1)M?
MA1.338(1)M?
Precision of 0.08
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Tests of GR
Based on R 1.07100.0009 ?16.8990.001
deg/yr (6x10-5)
Observed
Expected in GR
? 0.384 ms
? 0.3870.006 ms (10-2)
dPb/dt(-1.190.08) x10-12 (7x10-2)
dPb/dt-1.24x10-12
r 6.2 0.5 ?s (10-1)
r 6.2 ?s
s 0.9993 0.0004 (4x10-4)
s0.9997

• Best test in strong-field
• Non-radiative with
• fundamentally different constraints!

precision of 0.1!!
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Significance of R
To 1PN (v/c)2 order, relative separation given
by
e.g. Daumour Taylor 92
Qualitatively different constraint!
so that for any theory of gravity to 1PN
order
Ratio is independent of strong (self-)field
effects!
Different to other PK parameters, which all
depend on strong-field modified constants like
GAB which differs from GNewton depending on
strong-field effects in theory!
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Significance of R

• Beyond 1PN approximation, actual choice of
• coordinate system and mass definition becomes
• important and

may deviate from straight line in gt1PN but with
a precision which is probably much below what is
measurable or comparable for PK parameters.
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Outline
Introduction

• Pulsar properties
• Binary pulsars as gravity labs

The Double Pulsar

• Discovery of A and B
• A unique testbed for GR

The Future
76
Outline
Introduction

• Pulsar properties
• Binary pulsars as gravity labs

The Double Pulsar

• Discovery of A and B
• A unique testbed for GR

The Future
77
Predicted precision

• Difficult to predict behaviour of mass ratio
• For PK parms, precision increases by more but
  also
• more precise data

??/? ? T-1.5 expected since Science paper factor
4 actual improvement a factor of
100!
?sini/sini ? T-0.5 expected since Science paper
factor 1.6 actual improvement a
factor of 10!
Further expected scaling ??/? ? T-1.5
?(dPb/dt)/(dPb/dt) ? T-2.5
?d?/d? ? T -2.5
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Will we be able to use dPb/dt?

• Orbit shrinks 7mm/day
• Observed value biased by kinematics in units of

Observed -1.36 x 10-16 Vertical -1.26
x 10-20 Plane -3.10 x 10-20 Upper
limit on velocity from timing 17 km/s Velocity
from scintillation 66 km/s Shklovskii (17km/s)
5.25 x 10-20 Shklovskii (66km/s) 7.91 x 10-19
Needed correction lt 1
Also, VLBI observations underway
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Will we be able to use dPb/dt?

• Orbit shrinks 7mm/day
• Observed value biased by kinematics in units of

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Newly measurable PK parameters

• Relativistic orbit is deformed
• Two rather than a single eccentricity needed
  (DD86)

while the PK parameter
may be measurable in a few years
d? 12.6 x 10-6 expected
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Aberration

• Aberration contributes to timing and profile
• ToAs are modified by aberration delay (DD86)

However
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Aberration Geodetic Precession

• Aberration parameters will change due to
• geodetic precession

Damour Taylor (1992)
leading to different geometries, so that A
geometry may be determined! Expected
A -0.365?s x geometry!!
But spin-orbit coupling is likely to visible in
other ways too
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Spin contributions
We have seen that spin-coupling is large

• PK parameters are only expected to meet in
• a single point of mass-mass diagram IF spin
• contributions are negligible
• For instance, periastron advance is usually
• only used in 1PN approximation ignoring spin
• Formally, spin-orbit coupling enters at 1PN
  level!
• For binary pulsars however, numerically they are
• of size as 2PN effects (Wex 1995)

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Spin contributions
Total periastron advance at 2PN level Damour
Schaefer (1988)
Spin A
1PN
2PN
Spin B
Assuming canonical values 1PN 16.9
deg/yr 2PN
0.0004 deg/yr
SpinA 0.0002 deg/yr
already at 0.001deg/yr!
14 x 191316s value!
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Neutronstar structure
Total periastron advance to 2PN level Damour
Schaefer (1988)
Spin A
1PN
2PN
Spin B
Equation-of-State!
Measure NS moment of inertia!!!
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Summary

• Beautiful laboratory for plasma physics
• Invaluable for studying pulsar magnetospheres
• Unique test-bed for relativistic gravity
• Most over-constrained system already
• Only system with constraint independent of
  self-field
• Most precise tests already (So, far, Einstein is
  right!)
• More PK parameter/effects potentially
  measurable
• - Measurement of orbital deformation
• - Measurement of aberration
• Measurement of 2nd order PN effects
• (Lightbending, How do Keplers laws look
  like??)
• Moment of inertia Equation of State

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Finally
Hopefully, next time that you type double
pulsar into Google, you get something
different than this
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