pulsars + parkes = awesome
DESCRIPTION
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 - PowerPoint PPT PresentationTRANSCRIPT
Pulsars + Parkes = Awesome
Ryan Shannon Postdoctoral Fellow, CSIRO Astronomy and Space Science
Cre
dit:
John
Sar
kiss
ian
Ryan Shannon, Pulsars, Summer Vacation Seminar
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 Compact Remnant
White dwarf 0.1 to ~ 1.2 Msun
Degenerate electron pressure0.1 to 8 Msun
8 to 20 (?) Msun
> 20 Msun
Neutron star 1.3 to < 3 Msun
Degenerate neutron pressure
Black hole >3 Msun
Gravity wins
Complications: mass exchange in binary systems
Ryan Shannon, Pulsars, Summer Vacation Seminar
Background:1931: understanding of white dwarfs
(Chandrasekhar)1932: neutron discovered (Chadwick)1933: neutron stars (Baade & Zwicky)1939: first models (Oppenheimer & Volkoff)
Detectable? Thermal radiation (106 K, 10 km) bleak1967: Radio pulsars (serendipitous)
Gamma-ray bursts (ditto)
1968: Pulsar discovery announcedCrab pulsar discovered
1969: Crab pulsar spindown measured& clinched the NS hypothesis (T. Gold)
Historical background
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 explosion-
pulsar has high velocity (mashes up ISM)
• Pulsar: a class of neutron star that emits pulsed radiation
• Rotation powered -
Supernova 1987a, in the LMC
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
Pulsar radiation is pulsed
Single pulses from PSR B0834+06
• 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 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
• Two fundamental observables of pulsars
• 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
Per
iod
der
ivat
ive
(s s
-1)
Period (sec)
MSPs
Canonical Pulsars
Some pulsars are recycled
Ryan Shannon, Pulsars, Summer Vacation Seminar
Pulsar radiation is erratic
Bhat et. al.
• Single pulses vary in shape
• Some pulsars show ultra-bright giant pulses
• Some pulsars occasionally miss pulses (nulling)
• Some pulsars only occasionally emit pulses (rotating radio transients RRATS)
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 0 < DM < 1200 for known pulsars
Ryan Shannon, Pulsars, Summer Vacation Seminar
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
The Parkes radio telescope has found more than twice as many pulsars as the rest of the world’s telescopes put
together.
Talk to Mike Keith
Ryan Shannon, Pulsars, Summer Vacation Seminar26 May 2011 UWashington 14
• Repeat for L epochs spanning N=T/P spin periods (T=years)
• N ~ 108 – 1010 cycles in one year
• Period determined to
Pulsar Timing: The Basics of Pulsars as Clocks
• Stack M pulses (M=1000s) • Time-tag using template fitting
P …MP
W
• J1909-3744: eccentricity < 0.00000013 (Jacoby et al. 2006)
• B1937+21: P = 0.00155780649243270.0000000000000004 s
Ryan Shannon, Pulsars, Summer Vacation Seminar
What influences pulse arrival times?
• Pulsar spindown
• 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)
Pulsar
EarthGoal: including as many of the perturbations as possible in timing model.
Ryan Shannon, Pulsars, Summer Vacation Seminar
What influences pulsar arrival times?
te = tr – D/c2
+ DM/2
+ R + E + S
- R - E - S
+ TOAISM
+ TOAorbit noise
+ TOAspin noise
+ TOAgrav. waves
+ …
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
CASS Colloquium 3/8/11Insert presentation title, do not remove CSIRO from start of footer
pulsar
Earth
20 ms 10 µs 500 ns
Relative Day Relative Day
Relative Day
5 ms
Relative Day
No Spindown
Relative Amplitudes of Contributions
Simulated TOAs for MSP J1713+0747
Proper motion off by 1 mas/yr Parallax off by 1 masRA off by 1”
ΔT
ΔT ΔT
ΔT
0 1000 0 1000 0 1000
Relative Day0 1000
CASS Colloquium 3/8/11Insert presentation title, do not remove CSIRO from start of footer
Massive (white dwarf) companion
20 s
1000
ΔT
0 Relative Day
Reflex MotionKonacki & Wolszczan (2004): Three planets around MSP B1257+12: 4.3 MEarth,
3.9 MEarth, and 0.02 MEarth
1990 2002
2 ms
20 µs
20 µs
Ryan Shannon, Pulsars, Summer Vacation Seminar
Example: What pulsar residuals ought to look like: PSR B1855+09
Are
cib
o U
pg
rad
e
AO
Pai
nti
ng
The Residuals are quite white! (Time series from D. Nice)
Year1986 2010
ΔT
(µ
s)
6
-6
Ryan Shannon, Pulsars, Summer Vacation Seminar
Example: What Residuals from Most Pulsars Look Like
0 18
-50
40
ΔT
OA
(µ
s)
Time (yr)
Origin: Intrinsic spin instabilities (spin noise)Asteroid belt?
Ryan Shannon, Pulsars, Summer Vacation Seminar
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 SeminarCSIRO. Gravitational wave detection
• 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)
Gravitational Radiation from B1913+16
Ryan Shannon, Pulsars, Summer Vacation Seminar
The Next Grail: A double pulsar system
Ryan Shannon, Pulsars, Summer Vacation Seminar
First Double Pulsar: J0737-3939
• Pb=2.4 hrs, d/dt=17 deg/yr
• MA=1.337(5)M, MB=1.250(5)M
Lyne et al.(2004)
002.0000.1exp
obs
s
sTesting GR:
Kramer et al.(2004)
Now to 0.05%
Ryan Shannon, Pulsars, Summer Vacation Seminar
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 binaries2. Relic GWs from the early universe3. 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
• The induced timing residuals for different pulsars will be correlated
This is the same for all pulsars.
This depends on the pulsar.
Ryan Shannon, Pulsars, Summer Vacation Seminar
The expected correlation function
See Hellings & Downs 1983, ApJ, 265, L39
Simulated data
Ryan Shannon, Pulsars, Summer Vacation Seminar
Detection/limits on the background
• No detection yet made
• Good limit coming soon (see my talk next week!)
GW frequencies between 10-9 and 10-8 Hz - complementary to LIGO and LISA
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
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
Chatterjee et al. (2005)