1. and Astrophysics Frontiers
Pulsar Astronomy
and Astrophysics Frontiers
R. N. Manchester
CSIRO Astronomy and Space Science Australia Telescope National Facility, Sydney
Summary
Recent results from pulsar searches
Pulsar timing – glitches and period fluctuations
The Parkes Pulsar Timing Array (PPTA) project

2. Spin-Powered Pulsars: A Census
Currently 1973 known (published) pulsars
1788 rotation-powered disk pulsars
167 in binary systems
236 millisecond pulsars
141 in globular clusters
8 X-ray isolated neutron stars
15 AXP/SGR
20 extra-galactic pulsars
Data from ATNF Pulsar Catalogue, V1.41 ( (Manchester et al. 2005)

3. Great diversity in the pulsar population!.
The P – P Diagram
Galactic Disk pulsars
P = Pulsar period
P = dP/dt = slow-down rate . .
For most pulsars P ~ 10-15
MSPs have P smaller by about 5 orders of magnitude
Most MSPs are binary, but few normal pulsars are
tc = P/(2P) is an indicator of pulsar age
Surface dipole magnetic field ~ (PP)1/2 . . .
Great diversity in the pulsar population!

4. Recent Pulsar Searches
HTRU Parkes 20cm multibeam search
Mid-latitude survey
RRATs
More RRATs from the Parkes Multibeam Survey
Radio detections of Fermi sources
Fermi blind search

5. HTRU Parkes multibeam search
New digital backend system for the 13-beam 20cm Parkes system
1024 channels and 64 ms sampling (cf., PMPS 96 channels, 250 ms)
Survey in three parts:
High-latitude survey:
Dec < +10o, 270s/pointing
Mid-latitude survey:
-120o < l < +30o, |b| < 15o, 540s
Low-latitude survey:
-80o < l +30o, |b| < 3.5o, 4300s
Mid-latitude survey ~30% complete
27 pulsars detected so far, including 5 MSPs
(Keith et al. 2011)

6. PSR J1622-4950:a radio-loud magnetar
Radio (1.4 GHz) variability
Discovered in Parkes HTRU survey
P = 4.3 s, P = 1.7 x 10-11
Bs = 2.8 x 1014 G
tc = 4 kyr
Spin-down lum, E ~ 8.5 x 1033 erg s-1 . .
Radio emission flat spectrum, highly variable both in flux density and pulse shape
X-ray source detected by Chandra, luminosity ~ 2.5 x 1033 erg s-1
Possible SNR association
Chandra X-ray
ATCA 5.5 GHz
A magnetar in X-ray quiescence detected through its radio pulsations
(Levin et al. 2010)

7. HTRU RRATs Search 11 new RRATs discovered!
HTRU survey data searched for isolated dispersed pulses
Identified as Rotating Radio Transients (RRATs)
11 new RRATs discovered!
(Burke-Spolaor et al. 2011)

8. 1451 sources!
~100 pulsars!!

9. Fermi Gamma-ray Pulsars
98 pulsars now have detectable g-ray emission
- 7 detected by EGRET prior to Fermi launch in June 2008
30 are known young radio pulsars, e.g. Vela pulsar
13 are known radio millisecond pulsars (MSPs)
25 (young) pulsars discovered in blind g-ray searches
- 3 of these detected in deep radio searches
30 MSPs detected in radio searches of g-ray sources!!

10. The Vela Pulsar
Strong radio pulsar associated with Vela SNR
P = 89.3 ms, tc = 11.3 kyr
E = 6.9x1036 erg/s
Brightest g-ray source
g-ray pulses detected by SAS- 2 (1975), COS-B (1988), EGRET (1994), Fermi (2009)
Double g-ray profile
P1 lags radio by 0.14 periods
UV double pulse between g-ray main peaks .
Now 30 previously known young radio pulsars have g-ray pulse detections
(Abdo et al. 2009)

11. Fermi Detections of Known MSPs
Many MSPs have relatively high values of E/d2
Searches at positions of known MSPs using radio timing ephemeris
13 MSPs detected!
Generally g-ray pulse morphology and relationship to radio profiles similar to young pulsars .
(Abdo et al. 2009)

12. 25 pulsars detected! Blind Searches for Pulsars in Fermi Data
Many unidentified Fermi sources that have g-ray properties consistent with those of known pulsars
Some have associations with SNR, X-ray point sources, etc., but no known pulsar
Computationally impossible to search directly for periodicities – long data spans and not many photons
Time differences between photons up to a few weeks apart searched for periodicities
Once pulsations are detected, can do a timing analysis and get accurate period, period derivative and position
25 pulsars detected!

13. Fermi – CTA1 Pulsar First gamma-ray pulsar found in a blind search!
PSR J
(Abdo et al. 2008)

14. Fermi Blind-search Pulsars .
25 mostly young, high-E pulsars
Have pulse profiles very similar to radio- selected sample
Three have been detected as faint radio pulsars
PSR J detected at Arecibo, only 3 mJy!
Most have low upper limits on S1400 .
(Abdo et al. 2009, Saz Parkinson et al )

15. 17
(2010)

16. GBT Survey for pulsars associated with Fermi gamma-ray sources
GBT 100m telescope at 350 MHz, 100 MHz bw, 4096 chan., ms samp. int.
50 Fermi sources observed, observation time/pointing 32 min
10 MSPs discovered, P range: 1.6 ms – 7.6 ms
(Hessels et al. 2011)
Now 30 MSPs detected from radio searches of g-ray sources!

17. . E/d2 – Period Dependence . Radio-selected sample
Most high E/d2 pulsars have detected g-ray pulsed emission, for both young pulsars and MSPs
But some are not detected .
g-ray pulses detected: red dot
g-ray point source: green triangle
(Abdo et al., 2009)

18. Radio – g Beaming J
Two thirds of g-ray pulsars are also detected at radio wavelengths
All pulsars with E > erg s-1 are detected in both bands
Many have similar radio and g-ray pulse profiles
Some high-E/d2 radio pulsars are not (yet) detected by Fermi . . .
(Abdo et al. 2010)
Radio beams for high-E pulsars are wide!
For high E pulsars, both radio and g-ray emission regions are in the outer magnetosphere, sometimes but not always co-located .
(Ravi et al. 2010)

19. Pulsar Glitches
Sudden increase in spin rate of neutron star (n); typically Dn/n ~ x 10-9
Usually accompanied by increase in slow-down rate (|n|)
Increase in |n| often decays more-or-less exponentially with timescale in range 1 – 500 days . .
Probably due to sudden transfer of angular momentum to NS crust from faster rotating interior superfluid
(Espinoza et al. 2011)

20. Two Giant Glitches . . . PSR B2334+61: .. PSR J1718-3718: ..
Timed at Xinjiang Astronomical Observatory
P ~ s, tc ~ 41 kyr
Glitch in 2005, Dn/n ~ 20.5 x 10-6
Two exp. decays observed, td ~ 20 d, td ~ 150 d
Permanent increase in slow-down Dn/n ~ 1.1%
Also increase in n by factor of four
Possible ~350-day oscillation in n after glitch . . ..
(Yuan et al. 2010)
PSR J :
Timed at Parkes, at 1.4 and 3 GHz
P ~ 3.8 s, tc ~ 34 kyr, Bs ~ 7 x 1013 G
Glitch in 2007, Dn/n ~ 33.2 x 10-6
Little change in n at glitch
Significant decrease in n at glitch
- very unusal and not easily explained . ..
(Manchester & Hobbs 2011)

21. Change in magnetic structure and particle outflow at time of glitch
J in SNR Kes 75
Youngest known pulsar – tc ~ 800 yr
Discovered at X-rays, no radio detection
P ~ 326 ms, centred in SNR Kes 75
Large glitch Dn/n ~ 4 x 10-6 in 2006
Burst in X-rays at same time
Large increase in slow-down rate after glitch
Over-decay so that n less than pre- glitch extrapolation
Change in braking index: n(pre) = /- 0.01, n(post) = /- 0.13
(Livingstone et al. 2010,2011)
Change in magnetic structure and particle outflow at time of glitch

22. Pulsar Timing Arrays
A Pulsar Timing Array (PTA) is an array of pulsars widely distributed on the sky that are being timed with high precision with frequent observations over a long data span
PTA observations have the potential to detect a stochastic gravitational wave background from binary SMBHs in the cores of distant galaxies
Requires observations of ~20 MSPs over 5 – 10 years; could give the first direct detection of gravitational waves!
PTA observations can improve our knowledge of Solar system properties, e.g. masses and orbits of outer planets and asteroids
PTA observations can detect instabilities in terrestrial time standards and establish an ensemble pulsar timescale (EPT)
Idea first discussed by Hellings & Downs (1983), Romani (1989) and Foster & Backer (1990)

23. Global Effects in a PTA Clock errors Solar-System ephemeris errors
The three main global timing effects that can be observed with a PTA have different spatial signatures on the sky
Clock errors
All pulsars have the same TOA variations: monopole signature
Solar-System ephemeris errors
Dipole signature
Gravitational waves
Quadrupole signature
Can separate these effects provided the PTA contains a sufficient number of widely distributed pulsars

24. Detecting a Stochastic GW Background
A stochastic background of GWs in the Galaxy independently modulates both the pulse period emitted from a pulsar and the period observed at Earth
In a PTA, the modulations from GWs passing over the pulsars are uncorrelated
GWs passing over the Earth produce a correlated modulation of the signal from the different pulsars – it is this correlation that enables us to detect GWs!
The quadrupolar nature of GWs results in a characteristic correlation signature in the timing residuals from pulsar pairs which, for an isotropic stochastic background, is dependent only on the angle between the pulsars
The uncorrelated GWs passing over the pulsars reduces the maximum correlation to 0.5
It also introduces a “self-noise” in the correlations which is independent of ToA precision
Hellings & Downs correlation function
TEMPO2 simulation of timing-residual correlations due to a GW background for the PPTA pulsars
(Hobbs et al. 2009)

25. Major Pulsar Timing Array Projects
European Pulsar Timing Array (EPTA)
Radio telescopes at Westerbork, Effelsberg, Nancay, Jodrell Bank, (Cagliari)
Currently used separately, but plan to combine for more sensitivity
High-quality data (rms residual < 2.5 ms) for 9 millisecond pulsars
North American pulsar timing array (NANOGrav)
Data from Arecibo and Green Bank Telescope
High-quality data for 17 millisecond pulsars
Parkes Pulsar Timing Array (PPTA)
Data from Parkes 64m radio telescope in Australia
High-quality data for 20 millisecond pulsars
Observations at two or three frequencies required to remove the effects of interstellar dispersion

26. The Parkes Pulsar Timing Array Project
Using the Parkes 64-m radio telescope to observe 20 MSPs
~25 team members – principal groups: Swinburne University (Melbourne; Matthew Bailes), University of Texas (Brownsville; Rick Jenet), University of California (San Diego; Bill Coles), CASS, ATNF (Sydney; RNM, GH)
Observations at 2 – 3 week intervals at three frequencies: 732 MHz, 1400 MHz and 3100 MHz
New digital filterbank systems and baseband recorder system
Regular observations commenced in mid-2004
Timing analysis – PSRCHIVE and TEMPO2
GW simulations, detection algorithms and implications, galaxy evolution studies

27. The PPTA Pulsars

28. Best result so far – PSR J0437-4715 at 10cm
Observations of PSR J at 3100 MHz
1 GHz bandwidth with digital filterbank systems (PDFB1, 2 and 4)
3.1 years data span
374 ToAs, each 64 min observation time
Weighted fit for 12 parameters using TEMPO2
No dispersion correction
Reduced 2 = 2.46
Rms timing residual 55 ns!

29. 14 Years of Timing PSR J
Data from FPTM, CPSR1, CPSR2, WBC, PDFB1,2, (Verbiest et al PPTA)
Offsets between instruments determined from overlapping/adjacent data and then held fixed
Fit for position, pm, F0, F1, binary parameters
Clear evidence for long-term (“red”) period variations – origin?

30. Getting better, but more work to be done!
Current status:
Timing data at 2 -3 week intervals at 10cm or 20cm
PDFB2, 4 (1), spans 2.3 – 4.0 years
TOAs from 64-min observations (mostly; some 32 min)
Uncorrected for DM variations
Solve for position, F0, F1, Kepler parameters if binary
Four pulsars with rms timing residuals < 200 ns, 13 with < 1 s
Best results on J (55 ns), and J (95 ns)
Getting better, but more work to be done!
* Needs DM corrections # PCM calibration

31. Effect of Dispersion Measure Variations
PSR J
Six years of timing at 20cm (1.4 GHz) and 50cm (700 MHz)
Correlated residual variations with n-2 dependence – due to variations in interstellar dispersion
Must be removed for PTA applications
PSR J : DM correction reduces post-fit residuals by ~50%
Observed DM variations interesting for ISM studies
Before DM Correction
20cm post-fit
20cm
50cm
After DM Correction

32. Polarisation Calibration
20cm feed has significant cross-polar coupling (~ –10db)
Results in parallactic-angle dependence of pulse profile
Cross-coupling can be measured and profiles corrected using PSRCHIVE routines (PCM and PAC)
Results in large improvement for highly polarised pulsars, e.g. PSR J
3 years of PDFB2/4 data at 20cm
Before PCM correction:
Rms residual = 487 ns
Reduced c2 = 19.0
After PCM correction:
Rms residual = 195 ns
Reduced c2 = 3.1

33. Measuring Planet Masses with Pulsar Timing
Timing analysis uses Solar-System ephemeris (from JPL)
Error in planet mass leads to sinusoidal term in timing residuals
Obs of four pulsars, data from Parkes (CPSR2), Arecibo, Effelsberg:
J – (P) 13.5 yr
J – (P) 14.7 yr
J – (P,A,E) 23.8 yr
J – (P) 6.8 yr
Tempo2 modified to solve for planet mass using all four data sets simultaneously
Jupiter is best candidate:
DMJupiter = 5 x MSun
Best published value: ( ± 8) × 10-4 Msun
Pulsar timing result: ( ± 2) × 10-4 Msun
Unpub. Galileo result: ( ± 11) × 10-4 Msun
(Champion et al., 2010)
More pulsars, more data span, should give best available value!

34. Stochastic GWB Detection with PTAs
J06
J06
SMBH binary merger rate in galaxies is constrained by PTA observations
Model predictions for GW by Jaffe & Backer (JB03) and Sesana et al. (S0809)
Two cases: equal 109 M binary, equal 1010 M binary
Δ Obs. limit by Jenet et al. (J06)
× 20 psrs, 100 ns, 5 years
☐ 20 psrs, 500 ns, 10 years
O 20 psrs, 100 ns, 10 years
 100 psrs, 100 ns, 10 years
 100 psrs, 10 ns, 10 years
JB03
S0809
SKA will detect GWs!
(Wen et al. 2010)

35. The Gravitational Wave Spectrum

36. An Ensemble Pulsar Timescale (EPT)
Terrestrial time defined by a weighted average of cesium clocks at time centres around the world
TAI is (nearly) real-time atomic timescale
Revised by reweighting to give BIPMxxxx
Current best pulsars give a 10-year stability (z) comparable to TT(NIST) – TT(PTB) – two of the best atomic timescales
Pulsar timescale is not absolute, but can reveal irregularities in TAI and other terrestrial timescales
Analysis of “corrected” Verbiest et al. data sets for 18 MSPs using TEMPO2 and Cholesky method (Coles et al. 2010) to optimally deal with red timing noise
TAI – BIPM2010

37. EPT(PPTA2010) – Relative to TAI
BIPM2010
First realisation of a pulsar timescale with accuracy comparable to atomic timescales!
(Hobbs et al. 2010)

38. Summary
Several on-going pulsar searches are gradually increasing the number of known pulsars, especially millisecond pulsars
The Fermi Gamma-ray Observatory has increased the number of known g-ray-emitting pulsars by an order of magnitude
Radio and g-ray emission regions for high-E pulsars and MSPs are both high in the pulsar magnetosphere – sometimes co-located
Pulsar Timing Arrays have the potential to detect nHz gravitational waves and to establish the most precise long-term standard of time
Progress toward all goals will be enhanced by international collaboration - more (precise) TOAs and more pulsars are better!
Current efforts will form the basis for detailed study of GW and GW sources by future instruments with higher sensitivity, e.g. SKA .

39. GW from Formation of Primordial Black-holes
Black holes of low to intermediate mass can be formed at end of the inflation era from collapse of primordial density fluctuations
Intermediate-mass BHs (IMBH) proposed as origin of ultra-luminous X-ray sources; lower mass BHs may be “dark matter”
Collapse to BH generates a spectrum of gravitational waves depending on mass
Pulsar timing can already rule out formation of black holes in mass range 102 – 104 M!
(Saito & Yokoyama 2009)

40. Radio and g-ray Beaming
Approximate sky coverage by “top-hat” fan beams (integral over f of two-dimensional beam pattern)
Qr and Qg are equivalent widths of radio and g-ray beams respectively
Qc is the angular width of the overlap region
For a random orientation of rotation axes:
the relative number of pulsars detectable in band i is proportional to Qi
the relative number of pulsars detectable in both bands is proportional to Qc
In all cases Qr >= Qc
(Ravi, Manchester & Hobbs 2010)

41. Radio – g-ray Beaming
For the highest Edot pulsars, Qr >~ Qg
This implies that the radio beaming fraction fr is comparable to or greater than the g-ray beaming fraction fg
For OG and TPC models, fg ~ 1.0
For lower Edot Sample G pulsars, fr >~ 0.57 – includes several MSPs
Even high-altitude radio polar-cap models (e.g., Kastergiou & Johnston 2007) are unlikely to give fr >~ fg ~ 1
Therefore …
(Manchester 2005, Ravi et al. 2010)
For high Edot pulsars, it is probable that the radio emission region is located in the outer magnetosphere
Radio pulse profiles are formed in a similar way to g-ray profiles with caustic effects important

42. For both samples, the highest E pulsars are detected in both bands
Radio – g-ray Beaming
Two samples:
G: All pulsars found (or that could be found) in the Fermi 6- month blind search (Abdo et al )
R: High Edot radio pulsars searched by LAT for g-ray emission (Abdo et al. 2010)
Fraction of G and R samples with Edot > given value observed at both bands plotted as function of Edot
20/35 Sample G pulsars detected in radio band
17/201 Sample R pulsars detected in g-ray band
For both samples, the highest E pulsars are detected in both bands .
(Ravi, Manchester & Hobbs 2010)

43. Vela Pulsar Gamma-Ray Spectrum
Integrated spectrum from Fermi LAT
Power-law with exponential cutoff
Power-law index G = 1.38 ± 0.08
Exp. cutoff freq. Ec ~ 1.4 Gev
Super-exponential cutoff excluded
Implies that emission from high altitude in pulsar magnetosphere
PSR B

44. Modelling of g-ray pulse profiles
Two main models:
Outer-Gap model
Slot-Gap or Two-Pole Caustic model
OG model in red
TPC model in green
500 km altitude PC emission (radio) in aqua
(Watters et al. 2009)

45. Blind Detection of PSR J1022-5746
Most energetic blind Tc 4.6 kyr
HESS association - PWN
(Abdo et al. 2009)

46. PTA Pulsars: Timing Residuals
30 MSPs being timed in PTA projects world-wide
Circle size ~ (rms residual)-1
12 MSPs being timed at more than one observatory

47. Sky positions of all known MSPs suitable for PTA studies
In the Galactic disk (i.e. not in globular clusters)
Short period and relatively strong – circle radius ~ S1400/P
~60 MSPs meet criteria, but only ~30 “good” candidates
Current searches finding some potentially good PTA pulsars

48. Fermi Observations of Known Pulsars
In pre-Fermi era, seven pulsars known to emit g-ray pulses
Fermi scans whole sky every 3 hours – detected photons tagged with time, position and energy
Timing consortium using radio telescopes at Parkes, Green Bank, Arecibo, Nancay and Nanshan – timing solutions for 300+ pulsars with high E/d2 (E = 4p2IP/P3)
Photons with directions within PSF of known radio pulsar selected
Total data span usually many months, few x 1000 photons
Folded at known pulsar period and tested for periodicity
For detected sources, can form mean pulse profile in different energy bands and (for stronger sources) spectra for different time bins across pulse profile . . .

49. Fermi Detections of Young Radio Pulsars
PSR J
P = ms
tc = 20.3 kyr
E = 2x1036 erg/s
Marginal EGRET detection .
PSR J
P = 51.6 ms
tc = 10.5 kyr
E = 2x1037 erg/s
X-ray profile double but single at g-ray .
(Abdo et al. 2009)
Now 30 previously known young radio pulsars have g-ray pulse detections

50. Gravitational Waves
Prediction of general relativity and other theories of gravity
Generated by acceleration of massive objects
Propagate at the speed of light
Astrophysical sources:
Inflation era fluctuations
Cosmic strings
BH formation in early Universe
Binary black holes in galaxies
Black-hole coalescence and infall
Coalescing double-neutron-star binaries
Compact X-ray binaries
(K. Thorne, T. Carnahan, LISA Gallery)
These sources create a stochastic GW background in the Galaxy

51. Detection of Gravitational Waves
Generated by acceleration of massive objects in Universe, e.g. binary black holes
Huge efforts over more than four decades to detect gravitational waves
Initial efforts used bar detectors pioneered by Weber
More recent efforts use laser interferometer systems, e.g., LIGO, VIRGO, LISA
LIGO
LISA
Two sites in USA
Perpendicular 4-km arms
Spectral range 10 – 500 Hz
Initial phase now operating
Advanced LIGO ~ 2014
Orbits Sun, 20o behind the Earth
Three spacecraft in triangle
Arm length 5 million km
Spectral range 10-4 – 10-1 Hz
Planned launch ~2020

52. Timing Stability of MSPs
10-year data span for 20 PPTA MSPs
Includes 1-bit f/b, Caltech FPTM and CPSR2 data
sz: frequency stability at different timescales t
For “white” timing residuals, expect sz ~ t-3/2
Most pulsars roughly consistent with this out to 10 years
Good news for PTA projects!
10 ms
100 ns
(Verbiest et al. 2009)

53. Single-source Detection
Sensitivity
Localisation with PPTA
(Yardley et al. 2010)
First realistic sensitivity curve for a PTA system!
Computed GW strains for SMBH binary systems in Virgo cluster
PPTA can’t expect to detect individual systems - but SKA will!
(Anholm et al. 2008)
Need better sky distribution of pulsars - international PTA collaborations are important!

54. PTA Spin-offs PTA projects have many secondary objectives:
(Yan et al. 2010)
Studies of MSP and binary parameters and evolution
Pulsar astrometry
Pulsar polarisation and emission mechanisms
Interstellar medium – ne fluctuations and magnetic fields
Tests of gravitational theories
Galaxy and SMBH evolution and mergers
Instrumental and software development
- Low-noise broad-band receivers
Ultra-fast signal processing systems
Timing analysis systems and simulations
- RFI mitigation