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

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)

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!

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

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)

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)

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)

1451 sources! ~100 pulsars!!

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!!

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)

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)

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!

Fermi – CTA1 Pulsar First gamma-ray pulsar found in a blind search! PSR J0007+7303 (Abdo et al. 2008)

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 )

17 (2010)

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!

. 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)

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)

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)

Two Giant Glitches . . . PSR B2334+61: .. PSR J1718-3718: .. 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)

Change in magnetic structure and particle outflow at time of glitch 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

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)

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

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)

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

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

The PPTA Pulsars

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!

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?

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 J0437-4715 (55 ns), and J1909-3744 (95 ns) Getting better, but more work to be done! * Needs DM corrections # PCM calibration

Effect of Dispersion Measure Variations 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 Before DM Correction 20cm post-fit 20cm 50cm After DM Correction

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

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!

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)

The Gravitational Wave Spectrum

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

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

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 .

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)

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)

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

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. 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)

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

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)

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

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

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

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 . . .

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

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

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

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)

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!

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