Pulsar Searching and Timing R. N. Manchester CSIRO Astronomy and Space Science Sydney Australia Summary • Brief introduction to pulsars and timing • Searching for pulsars • Binary pulsars and tests of gravitational theories • Pulsar timing arrays and GW detection • The future Spin-Powered Pulsars: A Census

• Currently 2010 known (published) pulsars • 1846 rotation-powered disk pulsars • 186 in binary systems • 252 millisecond pulsars • 141 in globular clusters • 8 X-ray isolated neutron stars • 16 AXP/SGR • 20 extra-galactic pulsars

Data from ATNF Pulsar Catalogue, V1.44 (www.atnf.csiro.au/research/pulsar/psrcat) (Manchester et al. 2005) Pulsar Origins Pulsars are believed to be rotating neutron stars – two main classes: Normal Pulsars: • Formed in supernova • Periods between 0.03 and 10 s • Relatively young (< 107 years) (ESO – VLT) Millisecond Pulsars (MSPs): • Mostly single (non-binary) • MSPs are very old (~109 years). • Mostly binary • They have been ‘recycled’ by accretion from an evolving binary companion. • This accretion spins up the neutron star to millisecond periods. • During the accretion phase the system may be detectable as an X-ray binary system. Pulsars as Clocks • Neutron stars are tiny (about 25 km across) but have a mass of about 1.4 times that of the Sun • They are incredibly dense and have gravity 1012 times as strong as that of the Earth • Because of this large mass and small radius, their spin rates - and hence pulsar periods - are incredibly stable e.g., PSR J0437-4715 had a period of :

5.757451831072007 ± 0.000000000000008 ms • Although pulsar periods are very stable, they are not constant. Pulsars lose energy and slow down • Typical slowdown rates are less than a microsecond per year Measurement of pulsar periods • Start observation at a known time and average 103 - 105 pulses to get a mean pulse profile • Cross-correlate this with a standard template to give the arrival time at the telescope of a fiducial point on profile, usually the pulse peak – the pulse time-of-arrival (ToA) • Measure a series of ToAs over days – weeks – months – years • Transfer ToAs to an inertial frame - the Solar System barycentre • Compare barycentric ToAs with predicted values from a model for pulsar – the differences are called timing residuals. • Fit the observed residuals with functions representing errors in the model parameters (pulsar position, period, binary period etc.). • Remaining residuals may be noise – or may be science! Sources of Pulsar Timing “Noise”  Intrinsic noise • Period fluctuations, glitches • Pulse shape changes  Perturbations of the pulsar’s motion • Gravitational wave background • Globular cluster accelerations • Orbital perturbations – planets, 1st order Doppler, relativistic effects  Propagation effects • Wind from binary companion • Variations in interstellar dispersion • Scintillation effects  Perturbations of the Earth’s motion • Gravitational wave background • Errors in the Solar-system ephemeris  Clock errors • Timescale errors • Errors in time transfer  Instrumental errors • Radio-frequency interference and receiver non-linearities • Digitisation artifacts or errors • Calibration errors and signal processing artifacts and errors  Receiver noise Searching for Pulsars • Most pulsars havePRESTO been found Output in Page searches at radio frequencies • Pulsars have two main properties that are used to distinguish them

from (most) other radio signals: Frequency periodicity and dispersion • Multi-channel data sampled typically at ~100 µs intervals Time • Data summed in frequency with a range of dispersive delays and Fourier transformed • Searched in modulation frequency with harmonic summing • Candidates plotted and selected for confirmation • Observed again at same position to confirm periodicity and dispersion (www.cv.nrao.edu/~sransom/presto/) Parkes Multibeam Pulsar Survey • Covers strip along Galactic plane, -100o < l < 50o, |b| < 5o • Central frequency 1374 MHz, bandwidth 288 MHz, 96 channels/poln/beam • Sampling interval 250 µs, time/pointing 35 min, 3080 pointings • Survey observations commenced 1997, completed 2003 • Processed on work-station clusters at ATNF, JBO and McGill • 785 pulsars discovered, 1065 detected • At least 18 months of timing data obtained for each pulsar Principal papers: I: Manchester et al., MNRAS, 328, 17 (2001) System and survey description, 100 pulsars II: Morris et al., MNRAS, 335, 275 (2002) 120 pulsars, preliminary population statistics III: Kramer et al., MNRAS, 342, 1299 (2003) 200 pulsars, young pulsars and γ-ray sources IV: Hobbs et al., MNRAS, 352, 1439 (2004) 180 pulsars, 281 previously known pulsars V: Faulkner et al., MNRAS, 355, 147 (2004) Reprocessing methods, 17 binary/MSPs VI: Lorimer et al., MNRAS, 372, 777 (2006) 142 pulsars, Galactic population and evolution Other Recent Surveys • PALFA Survey (Cordes et al. 2006)  7-beam feed on Arecibo, ~1400 MHz  21 pulsars discovered so far • Fermi Radio IDs (Hessels et al. 2011, Kerr et al. 2012)  Various radio telescopes  ~20 discoveries, mostly MSPs • Fermi Blind searches (Pletsch et al. 2012)  Search for periodicities in gamma-ray data  33 discoveries, mostly young pulsars • HTRU survey (Keith et al. 2010)  Parkes MB receiver with digital backend system  33 pulsars so far The Parkes radio telescope has found twice as many pulsars as the rest of the world’s telescopes put together! Parkes Multibeam Pulsar. Surveys: the P – P Diagram J1119-6127 • New sample of young, high-B, long- period pulsars • Large increase in sample of mildly recycled binary pulsars • Three new double- neutron-star systems J0737-3039A and one double pulsar! Tests of Gravitational Theories

• PSR B1913+16, discovered at Arecibo by Russell Hulse & Joe Taylor in 1975 • First-known binary pulsar, orb. period 7.75 h • Double-neutron-star system – relativistic orbit perturbations detectable  First accurate measurement of n-star mass  First observational evidence for gravitational waves  Confirmation of general relativity as an accurate theory of gravity Nobel Prize for Hulse and Taylor in 1993! (Weiserg & Taylor 2005) PSR J0730-3039A/B The first double pulsar!

• Discovered in Parkes high-latitude

multibeam pulsar survey John Rowe Animations • Two pulsars orbiting each other every 2.4 hours

• PA = 22 ms, PB = 2.7 s • Five relativistic orbit perturbations detected • Best strong-field test so far of Einstein’s general theory of

relativity (Burgay et al., 2003; Lyne et al. 2004) (Kramer et al. 2006) Measured Post-Keplerian Parameters for PSR J0737-3039A/B

GR value Measured value Improves as . ω Periast. adv. (deg/yr) - 16.8995 ± 0.0007 T1.5

γ Grav. Redshift (ms) 0.3842 0.386 ± 0.003 T1.5 . -12 -12 2.5 Pb Orbit decay -1.248 x 10 (-1.252 ± 0.017) x 10 T r Shapiro range (µs) 6.15 6.2 ± 0.3 T0.5

+16 0.5 s Shapiro sin i 0.99987 0.99974 - 39 T Consistent with GR at the 0.05% level! Non-radiative test - distinct from PSR B1913+16 (Kramer et al. 2006) Updated PSR J0737-3039A/B Mass-Mass Diagram

• Analysis of GBT and Parkes timing data to 2011 • All parameters improved – now best measurement of orbit decay due to GW emission • Includes spin-orbit coupling from eclipse analysis (Kramer et al. 2012) Detection of Gravitational Waves • Prediction of general relativity and other theories of gravity • Generated by acceleration of massive object(s) • Astrophysical sources:  Inflation era fluctuations  Cosmic strings  BH formation in early Universe  Binary black holes in galaxies  Coalescing neutron-star binaries  Compact X-ray binaries

(K. Thorne, T. Carnahan, LISA Gallery) A Pulsar Timing Array (PTA)

• With observations of many pulsars widely distributed on the sky can in principle detect a stochastic gravitational wave background • Gravitational waves passing over the pulsars are uncorrelated • Gravitational waves passing over Earth produce a correlated signal in the TOA residuals for all pulsars • Requires observations of ~20 MSPs over 5 – 10 years; could give the first direct detection of gravitational waves! • A timing array can detect instabilities in terrestrial time standards – establish a pulsar timescale • Can improve knowledge of Solar system properties, e.g. masses and orbits of outer planets and asteroids Idea first discussed by Hellings & Downs (1983), Romani (1989) and Foster & Backer (1990) 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 µs) 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 Agreement on combining data sets to form the International Pulsar Timing Array (IPTA) The Parkes Pulsar Timing Array Collaboration  CSIRO Astronomy and Space Science, Sydney Dick Manchester, George Hobbs, Ryan Shannon, Mike Keith, Sarah Burke-Spolaor, Aidan Hotan, John Sarkissian, John Reynolds, Mike Kesteven, Warwick Wilson, Grant Hampson, Andrew Brown, Ankur Chaudhary, (Russell Edwards), (Jonathan Khoo), (Daniel Yardley)  Swinburne University of Technology, Melbourne Matthew Bailes, Willem van Straten, Stefan Oslowski, Andrew Jameson, (Ramesh Bhat), (Jonathon Kocz)  Monash University, Melbourne Yuri Levin  University of Melbourne Vikram Ravi (Stuart Wyithe)  University of California, San Diego Bill Coles  University of Texas, Brownsville (Rick Jenet)  MPIfR, Bonn (David Champion), (Joris Verbiest), (KJ Lee) Southwest University, Chongqing Xiaopeng You  Xinjiang Astronomical Observatory, Urumqi (Wenming Yan), Jingbo Wang  National Space Science Center, Beijing Xinping Deng The PPTA Pulsars

All (published) MSPs not in globular clusters PPTA “Best” Data Sets • 6-year data span • Lowest rms residuals for: J0437-4715 – 75 ns J1909-3744 – 133 ns (both at 10cm) • Significant “red” noise • “White” rms residuals: J0437-4715 – 46 ns J1909-3744 – 61 ns Extended PPTA Data Sets • Parkes data from Swinburne timing program for 1994 – 2006 (Verbiest et al. 2008, 2009) added to PPTA three-band data sets • Extended data sets cover up to 17 years • Most instrumental offsets measured from overlapping data and fixed • DM offsets included and held fixed • Fit with Cholesky algorithm to pulsar parameters and remaining instrumental offsets • Fit to just F0, F1 for best-band data; all other parameters fixed Current Limits on GW Background Characteristic strain spectrum: For a stochastic background from binary SMBBH, α = -2/3

EPTA: 7 MSPs, 10 yrs, A < 6 x 10-15 (van Haasteren et al. 2011) NANOGrav: 17 MSPs, 5.5 yrs, A < 7.2 x 10-15 (Demorest et al 2012) PPTA: 19 MSPs, up to 17 yrs, A < 2.4 x 10-15 (Shannon et al 2012) New method, better data sets PPTA Limit for Stochastic GW Background

Range of predictions by Sesana et al. (2008)

(1 yr)-1

(Shannon et al. 2012) Future Prospects • Continuing searches will increase number of known pulsars, especially MSPs • Continuing timing of the Double Pulsar and other pulsar binaries will allow more stringent tests of GR and may reveal inconsistencies in the GR predictions • Combination of extended PTA data sets to make IPTA should give a detection of the stochastic GW background Sensitivity of a PTA to a stochastic GW background Black: 20 psrs Red: 50 psrs Blue: 200 psrs Plain line: 5 yrs Line with ×: 10 yrs (Sesana prediction) Line with o: 20 yrs (Manchester et al. 2012) Single Sources • Likely that many SMBH binary systems are highly eccentric • GW spectrum may be dominated by a strong individual source

First GW detection by PTAs could be a single source with period <~ 1 year!

(Sesana 2012) The International Pulsar Timing Array • The IPTA is a consortium of consortia, namely existing PTAs from around the world • Currently three members: EPTA, NANOGrav and PPTA • The aims of the IPTA are to facilitate collaboration between participating PTA groups and to promote progress toward PTA scientific goals • The IPTA has a Constitution which states these points and defines the rules under which it operates • There is a Steering Committee which sets policy guidelines for data sharing, publication of results etc. • The IPTA organises annual Student Workshops and Science Meetings – 2013 meetings will be in Krabi, Thailand, June 17-28 • The IPTA would welcome approaches from new timing consortia IPTA Website: www.ipta4gw.org IPTA Wiki: www.ipta4gw/wiki

• Main working area for IPTA business – accessible to members of participating PTAs • Contains pages for policy documents, shared data release, IPTA projects and preprints, Steering Committee Minutes, etc. • Requires approved “User” status to view (all) and edit (most) pages New Instruments MEERKAT – SKA 1 (Sth Africa) • 250 x 15m dishes, single pixel feeds • 3 bands: 0.5 – 3.0 GHz • Collecting area ~ Arecibo • Complete ~2019 • Good for pulsar timing ASKAP – SKA 1 (Australia) • 100 x 15m dishes, PAFs – 100 beams over 30 sq. degrees • 0.7 – 1.7 GHz • ~50% area within 1 km core • Good for searches and timing of “normal” pulsars FAST – 500m DiameterFAST now! Reflector in China • In Guizhou Province in Completion ~2016 south China – karst region • Arecibo-type dish, ~ twice Arecibo sensitivity • Max zenith angle 40 deg (60 deg later) • 0.07 – 3.0 GHz in several bands (8 GHz later) • 19-beam 20cm receiver Pulsar searches: • In 200 8-hr days, ~5000 pulsars including 500 MSPs • In 80 6-hr days, ~100 extragalactic pulsars (M31/M33) Pulsar Timing: • Could time ~50 MSPs /day – expect to have CPTA joining IPTA! More Distant Future Square Kilometer Array – Phase 2 • Mid-frequency array in South Africa • 3000 x 15m dishes • Area ~5 x FAST • But ~20% within 1 km • With PAFs – fantastic survey instrument, speed ~25 x FAST • But computing requirements horrendous: 100’s GB/s, 100 TB RAM • Can’t store raw data: ~10 petaflop computing to process in real time • Complete 2023+ • Could discover 20,000 pulsars, 5000 MSPs

(J Cordes) Summary • Pulsars, especially MSPs, are incredibly precise celestial clocks • Now ~2000 known pulsars, including ~250 MSPs • Pulsar timing is a powerful technique with many applications • Timing of the Double Pulsar has shown that GR is accurate at the 0.02% level in strong gravity and given the most accurate measurement of orbit decay due to GW emission • Pulsar timing arrays have set interesting limits on the level of a stochastic GW background at nanoHertz frequencies • Combination of data to form the IPTA will improve these results and should lead to a direct detection of GW in the next few years • Future instruments will greatly increase the number of known pulsars and will enable the detailed study of nanoHertz GW and their sources as well as greatly improved results for other PTA objectives

The Gravitational Wave Spectrum  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 there is a sufficient number of widely distributed pulsars Detecting a Stochastic GW Background • Super-massive black-hole binary (SMBHB) systems in the cores of distant galaxies (formed through galaxy mergers) will generate a stochastic background of GWs in the Galaxy

• PTAs are sensitive to GW with periods of years: PGW = PSMBHB/2 • Pulsar period modulations from GWs passing over different pulsars are uncorrelated • GWs passing over the Earth produce a correlated modulation in the periods of different pulsars – it is this correlation that enables us to detect GWs! • For an isotropic stochastic background, the correlation signature Hellings & Downs correlation function in the timing residuals from pulsar pairs is dependent only on the angle between the pulsars • Anti-correlation for angles ~90o because of quadrupolar nature of GWs TEMPO2 simulation of timing- residual correlations due to a GW background for the PPTA pulsars (Hobbs et al. 2009) . 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 . • τc = P/(2P) is an indicator of pulsar age • Surface. dipole magnetic field ~ (PP)1/2 Great diversity in the pulsar population!