Credit: John Sarkissian
Pulsars + Parkes = Awesome
Ryan Shannon
Postdoctoral Fellow, CSIRO Astronomy and Space Science
Outline
• Post main sequence stellar
evolution
• A few of the properties of pulsars
that make them hella cool.
• Pulsar timing: the bread and
butter of pulsar observing
• What I like about pulsars:
Get to work on a lot of different
areas of physics and
astrophysics
Crab Pulsar Wind Nebula
Ryan Shannon, Pulsars, Summer Vacation Seminar
End of Stellar Evolution
Main sequence star
0.1 to 8 Msun
Compact Remnant
White dwarf 0.1 to ~ 1.2 Msun
Degenerate electron pressure
8 to 20 (?) Msun
Neutron star 1.3 to < 3 Msun
Degenerate neutron pressure
> 20 Msun
Black hole
Gravity wins
Complications: mass exchange in binary systems
Ryan Shannon, Pulsars, Summer Vacation Seminar
>3 Msun
Historical background
Background:
1931:
1932:
1933:
1939:
Detectable?
1967:
understanding of white dwarfs
(Chandrasekhar)
neutron discovered (Chadwick)
neutron stars (Baade & Zwicky)
first models (Oppenheimer & Volkoff)
Thermal radiation (106 K, 10 km)  bleak
Radio pulsars (serendipitous)
Gamma-ray bursts (ditto)
1968:
Pulsar discovery announced
Crab pulsar discovered
1969:
Crab pulsar spindown measured
& clinched the NS hypothesis (T. Gold)
Ryan Shannon, Pulsars, Summer Vacation Seminar
How to build a pulsar in 50 Mega year
• Maser
• Massive Star
• Supernova explosion
• Neutron Star
• Conservation of angular
momentum: spins fast
• Conservation of magnetic
flux: high magnetic fields.
• Compact ~ 1.4 solar masses
of material in 10 km.
• Assymetric SN explosionpulsar has high velocity
(mashes up ISM)
• Pulsar: a class of neutron
star that emits pulsed
radiation
• Rotation powered -
Ryan Shannon, Pulsars, Summer Vacation Seminar
Supernova 1987a, in the LMC
Pulsar radiation is pulsed
• Periodicity of the emission: rotation
period of neutron star
• Spin period for radio-bright neutron
stars 1 ms to 10 s
• Emission region: located near
magnetic pole of star
Ryan Shannon, Pulsars, Summer Vacation Seminar
Pulsar radiation is pulsed
• Periodicity of the emission: rotation
period of neutron star
• Spin period for radio-bright neutron
stars 1 ms to 10 s
• Emission region: located near
magnetic pole of star
Ryan Shannon, Pulsars, Summer Vacation Seminar
Single pulses from PSR B0834+06
Pulsar radiation is periodically pulsed
• Each pulsar has a unique
fingerprint (pulse profile)
• Pulsed emission averages
towards a standard that is
usually statistically identical at all
observing epochs
• If the profile stays the same, we
can very accurately track the
rotation history of the pulsars
• Precision pulsar timing: most
powerful use of pulsars (next to
CMB, the most powerful use of
any form of astrophysical
radiation)
Ryan Shannon, Pulsars, Summer Vacation Seminar
Pulsars have unique Period and Period derivatives
• Period
• Period derivative
• Describe the pulsar
population
• Estimate other
properties based on P
and Pdot.
• Age (103 – 109 yr)
• Surface magnetic field
strength (108 to1015 G)
• Surface voltage
potential (1012 V)
log Period derivative (s s-1)
• Two fundamental
observables of pulsars
Canonical
Pulsars
MSPs
Some pulsars are
recycled
Period (sec)
Ryan Shannon, Pulsars, Summer Vacation Seminar
Pulsar radiation is erratic
• Single pulses vary in shape
• Some pulsars show ultrabright giant pulses
• Some pulsars occasionally
miss pulses (nulling)
• Some pulsars only
occasionally emit pulses
(rotating radio transients
RRATS)
Bhat et. al.
Ryan Shannon, Pulsars, Summer Vacation Seminar
Pulsar radiation is dispersed
• Warm plasma in the ISM is
refractive, and the index of
refraction depends on RF.
• At higher frequencies pulsed
emission arrive earlier
• Level of dispersion depends on
total column density along the line
of sight (Dispersion measure DM).
• Dispersion is an excellent
discriminator
• Allows us to distinguish pulsars
from RFI (radar, microwaves, guitar
hero)
• Corollary: Pulsars can be used to
study ISM and Galactic Structure
Ryan Shannon, Pulsars, Summer Vacation Seminar
0 < DM < 1200 for known pulsars
Pulsar Radiation is Multi-wavelength
• Non-thermal emission observed across entire EM spectrum
• Some pulsars are prodigious producers of gamma-ray
emission.
• The number of high energy pulsars has grown by a factor
of 10 since the launch of the Fermi space telescope.
Ryan Shannon, Pulsars, Summer Vacation Seminar
Step 1: Finding Pulsars
Talk to Mike Keith
The Parkes radio telescope has found more than twice as
many pulsars as the rest of the world’s telescopes put
together.
Ryan Shannon, Pulsars, Summer Vacation Seminar
Pulsar Timing: The Basics of Pulsars as Clocks
P
•
•
MP
…
Stack M pulses (M=1000s)
Time-tag using template fitting
W
• Repeat for L epochs spanning N=T/P spin periods (T=years)
• N ~ 108 – 1010 cycles in one year
• Period determined to
• B1937+21:
P = 0.00155780649243270.0000000000000004 s
• J1909-3744: eccentricity < 0.00000013 (Jacoby et al. 2006)
26 May 2011Ryan Shannon, Pulsars, Summer Vacation Seminar
UWashington
14
What influences pulse arrival times?
• Pulsar spindown
Pulsar
• Random spindown variations
• Intrinsic variation in shape and/or
phase of emitted pulse (jitter)
• Reflex Motion from companions
• Gravitational Waves
• Pulsar position, proper motion,
distance
• Warm electrons in the ISM
• Solar system
• Mass of planets (Champion et
al. 2010)
• Location of solar system
barycentre (John Lopez)
Goal: including as many of the
perturbations as possible in timing
model.
Ryan Shannon, Pulsars, Summer Vacation Seminar
Earth
What influences pulsar arrival times?
te = tr –
+ DM/2
+ R + E + S
- R - E - S
+ TOAISM
+ TOAorbit noise
+ TOAspin noise
+ TOAgrav. waves
+…
D/c2
Path length
Plasma dispersion (ISM)
Solar system (Roemer, Einstein, Shapiro)
Binary pulsar (R,E,S delays)
ISM scattering fluctuations
Orbital perturbations
Intrinsic spin (torque) noise
Gravitational wave backgrounds
Want to include as many of these perturbations as
possible in model
Ryan Shannon, Pulsars, Summer Vacation Seminar
No Spindown
ΔT
Relative Amplitudes of
Contributions
pulsar
5 ms
0
Relative Day
Simulated TOAs for MSP
J1713+0747
Earth
1000
Relative Day
Parallax off by 1 mas
20 ms
0
CASS Colloquium 3/8/11
1000
10 µs
0
Relative Day
1000
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Day
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ΔT
Proper motion off by 1 mas/yr
ΔT
ΔT
RA off by 1”
500 ns
0
Relative Day
1000
Reflex Motion
Konacki & Wolszczan (2004):
Three planets around MSP
B1257+12: 4.3 MEarth,
3.9 MEarth, and 0.02 MEarth
Massive (white dwarf)
companion
2 ms
ΔT
20 µs
20 s
20 µs
0
Relative Day
CASS Colloquium 3/8/11
1000
1990
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2002
Example: What pulsar residuals ought to look like: PSR B1855+09
AO Painting
ΔT (µs)
Arecibo Upgrade
6
-6
1986
Year
The Residuals are quite white! (Time series from D. Nice)
Ryan Shannon, Pulsars, Summer Vacation Seminar
2010
Example: What Residuals from Most Pulsars Look Like
40
ΔTOA (µs)
Origin:
Intrinsic spin instabilities (spin noise)
Asteroid belt?
-50
0
Time (yr)
Ryan Shannon, Pulsars, Summer Vacation Seminar
18
Applications of pulsar timing
• Neutron stars with companions
• Known companions: white dwarfs, neutron stars, planets
• Need to incorporate general relativity to model orbits of WD and
NS binary systems
• Tests of general relativity
• Holy grails:
• A pulsar orbiting another pulsar (two clocks, dude)
• Pulsar orbiting a black hole
• Direct detection of gravitational waves
• What Ryan works on: understanding astrophysical “noise” in
timing observations
Ryan Shannon, Pulsars, Summer Vacation Seminar
First binary pulsar: The Hulse-Taylor Binary
B1913+16
Pulse period: 59 ms
Orbital Period: 7h
45m
Double neutron-star
system
Velocity at periastron: ~0.001 of velocity of
light
•Periastron advance: 4.226607(7) deg/year
(same advance in a day as Mercury
advances in a century)
Ryan Shannon, Pulsars, Summer Vacation Seminar
Gravitational Radiation from B1913+16
• Prediction based on
measured Keplerian
parameters and Einstein’s
general relativity due to
emission of gravitational
waves (1.5cm per orbit)
•After ~250 MYr the two
neutron stars will collide!
(Weisberg & Taylor 2003)
CSIRO.
Gravitational
waveSummer
detection
Ryan Shannon,
Pulsars,
Vacation Seminar
The Next Grail: A double pulsar system
Ryan Shannon, Pulsars, Summer Vacation Seminar
First Double Pulsar: J0737-3939
Lyne et al.(2004)
• Pb=2.4 hrs, d/dt=17 deg/yr
• MA=1.337(5)M, MB=1.250(5)M
Now to 0.05%
Ryan Shannon, Pulsars, Summer Vacation Seminar
Testing GR:
s obs
 1.000  0.002
exp
s
Kramer et al.(2004)
The Future: Pulsar Black Hole Systems
• Pulsar-BH binaries in the field
• Pulsars orbiting Sag A* (Massive black hole in centre of
Galaxy)
Ryan Shannon, Pulsars, Summer Vacation Seminar
Gravitational Wave Detection with Pulsars
Ryan Shannon, Pulsars, Summer Vacation Seminar
Status of gravitational wave detections:
Number of known gravitational wave sources:
0
Ryan Shannon, Pulsars, Summer Vacation Seminar
Spin-down irregularities
No angular signature
Ryan Shannon, Pulsars, Summer Vacation Seminar
What if gravitational waves exist?
Quadrapolar signature
Ryan Shannon, Pulsars, Summer Vacation Seminar
A stochastic background of GW sources
Expect backgrounds from:
1. Supermassive black-hole binaries
2. Relic GWs from the early universe
3. Cosmic strings
The stochastic background is made up of a sum of a large
number of plane gravitational waves.
Ryan Shannon, Pulsars, Summer Vacation Seminar
Detecting the stochastic background
This is the same for all pulsars.
This depends on the pulsar.
• The induced timing residuals for different pulsars will be
correlated
Ryan Shannon, Pulsars, Summer Vacation Seminar
The expected correlation function
Simulated data
See Hellings & Downs 1983, ApJ, 265, L39
Ryan Shannon, Pulsars, Summer Vacation Seminar
Detection/limits on the background
• No detection yet made
• Good limit coming soon
(see my talk next week!)
Current data sets
are ruling out a few
cosmic string
models
The square kilometre
array should detect
GWs or rule out most
models
Ryan Shannon, Pulsars, Summer Vacation Seminar
GW frequencies
between 10-9 and
10-8 Hz complementary to
LIGO and LISA
Conclusion
• Pulsars: the end state for
intermediate mass stars
• Pulsars can be used to study
many different aspects of
astronomy and astrophysics
• Pulsar timing has been and
continues to be a powerful
physical and astrophysical probe.
• Thank you!
Ryan Shannon, Pulsars, Summer Vacation Seminar
Pulsars Have High Velocities:
• VLBI: parallax, proper motion
• Pulsar distance:
• NS Population model
• Luminosity (particularly for high energy
emission)
• Constrain Galactic electron density
model/ Galactic structure
• Pulsar velocity: High velocity some >
1000 km/s (escape the Galaxy)
• Physics of supernvova explosions
• Synthesis imaging: Pulsar
environment / Pulsar wind nebulae
(PWN)
• Interactions between pulsar wind and
the ISM produce synchrotron
emission
Ryan Shannon, Pulsars, Summer Vacation Seminar
Chatterjee et al. (2005)