Pulsar Astronomy and Astrophysics Frontiers

1. 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 (www.atnf.csiro.au/research/pulsar/psrcat) (Manchester et al. 2005)

3. . The P – P Diagram Galactic Disk pulsars P = Pulsar period P = dP/dt = slow-down rate . . • For most pulsars P ~ 10-15 • MSPs haveP 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 • 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. 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 J0007+7303 (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 J1907+0602 detected at Arecibo, only 3 mJy! • Most have low upper limits on S1400 (Abdo et al. 2009, Saz Parkinson et al. 2010 )

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., 81.92 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 . (Abdo et al., 2009) • g-ray pulses detected: red dot • g-ray point source: green triangle

18. Radio – g Beaming J0034-0534 • Two thirds of g-ray pulsars are also detected at radio wavelengths • All pulsars with E > 1037 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 ~ 1 - 5000 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: • Timed at Xinjiang Astronomical Observatory • P ~ 0.495 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 J1718-3718: • 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. J1846-0258 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) = 2.65 +/- 0.01, n(post) = 2.16 +/- 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 ensemblepulsar timescale(EPT) Idea first discussed by Hellings & Downs (1983), Romani (1989) and Foster & Backer (1990)

23. Global Effects in a PTA 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 Quadrupolesignature 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 todetect 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 J0437-4715 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 J0437-4715 • Data from FPTM, CPSR1, CPSR2, WBC, PDFB1,2,4 (Verbiest et al. 2008 + 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. 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 J0437-4715 (55 ns), and J1909-3744 (95 ns) Getting better, but more work to be done! * Needs DM corrections # PCM calibration

31. Effect of Dispersion Measure Variations Before DM Correction • PSR J1045-4509 • 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 J1045-4509: DM correction reduces post-fit residuals by ~50% • Observed DM variations interesting for ISM studies 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 J1744-1134 • 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: • J0437-4715 – (P) 13.5 yr • J1744-1134 – (P) 14.7 yr • J1857+0943 – (P,A,E) 23.8 yr • J1909-3744 – (P) 6.8 yr • Tempo2 modified to solve for planet mass using all four data sets simultaneously • Jupiter is best candidate: DMJupiter = 5 x 10-10 MSun Best published value: (9.547919 ± 8) × 10-4 Msun Pulsar timing result: (9.547922 ± 2) × 10-4 Msun Unpub. Galileo result: (9.54791915 ± 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 • O20 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 EPT 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 … • 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 (Manchester 2005, Ravi et al. 2010)

42. 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. 2010) • 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 B0833-45

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 J1048-5832 • P = 123.7 ms • tc = 20.3 kyr • E = 2x1036 erg/s • Marginal EGRET detection . • PSR J2229+6114 • 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