Gravitational Wave and Pulsar Timing Xiaopeng You Jinlin

Gravitational Wave and Pulsar Timing Xiaopeng You, Jinlin Han, Dick Manchester National Astronomical Observatories, Chinese Academy of Sciences

Outline • Gravitational Wave – Physics of gravitational waves – Gravitational wave detection – Gravitational wave sources • Detecting G-wave by Pulsar Timing – Introduction to pulsar timing – PPTA project – Directly detecting gravitational wave • Effect of ISM on Pulsar Timing – Dispersion measure change – Scintillation

Gravitational Wave: Ripples in Spacetime! • Einstein field equation • Weak field approximation • Gravitational wave equation

Properties of G-wave • Quadrupole moment • Two polarization states “+” “×” • Generation of G-waves

G-wave Detection • Interferometer detector – Basic formula: – LIGO: h~10 -22, L=4 km, L~10 -17 cm – LISA: h~10 -21, L=5× 106 km, L~10 -10 cm • Pulsar timing as G-wave detector – See pulsar timing part

G-wave Sources • High frequency (10 ~ 104 Hz, LIGO Band) – – – Inspiraling compact binaries (NS and BH, MBH 103 M ) Spinning neutron star Supernovae Gamma ray bursts Stochastic background • Low frequency (10 -4 ~ 1 Hz, LISA Band) – – – Galactic binaries Massive BH binary merger (104 M MBH 109 M ) MBH capture of compact object Collapse of super massive star Stochastic background

G-wave Sources • Very low frequency (10 -9 ~ 10 -7 Hz, pulsar timing) – Processes in the very early universe • Big bang • Topological defects, cosmic strings • First-order phase transitions – Inspiral of super-massive BH (MBH>1010 M ) • Extremely low frequency (10 -18 ~ 10 -15 Hz) – Primordial gravitational fluctuations amplified by the inflation of the universe – Method: imprint on the polarization of CMB radiation

Pulsar Timing • Pulsars are excellent celestial clocks, especially MSP • Basic pulsar timing observation • The timing model, inertial observer • Correct observed TOA to SSB • Series TOAs corrected to SSB: ti • Least squares fit time residual

Modeling Timing Residual and Timing “Noise” From Hobbs et al. (2005)

Source of Timing Noise • • Receiver noise Clock noise Intrinsic noise Perturbations of pulsar motion – G-wave background – Globular cluster accelerations – Orbital perturbations • Propagation effects – Wind from binary companion – Variants in interstellar dispersion – Scintillation effects • Perturbations of Earth’s motion – G-wave background – Errors in the Solar-system ephemeris

Indirect evidence of G-wave PSR B 1913+16 • First observational evidence of G-wave Nobel Prize for Taylor & Hulse in 1993 ! From Weisberg & Taylor (2003)

Detect G-wave by pulsar timing Photon Path Pulsar w G e v a Earth • Observation one pulsar, only put limit on strength of G-wave background • New limits on G-wave radiation (Lommen, 2002)

Direct detection of G-wave • Observation of many pulsars • Effect of G-wave background – Uncorrelated on individual pulsars – But correlated on the Earth • Method: two point correlation • Sensitive wave frequency 10 -8 Hz

PPTA project • • Goal: detect G-wave & establish PSR timescale Timing, 20 MSPs, 2 -3 week interval, 5 years 3 frequencies: 700 MHz, 1400 MHz and 3100 MHz TOA precision: 100 ns > 10 pulsars, 1 s for others

Detect G-wave background Simulation using PPTA pulsars with G-wave background from SMBH (Jenet et al. )

Detect G-wave background G-wave from SMBH A) Simple correlation, B) Pre-whiten 20 psrs, 100 ns, 250 obs, 5 years Low-pass filtering 20 psrs, 100 ns, 500 obs, 10 years 20 psrs, 100 ns, 250 obs, 5 years 10 psrs, 100 ns, 10 psrs, 500 ns, 250 obs, 5 years From Jenet et al. (2005) 10 psrs, 100 ns, 250 obs, 5 years

ISM Effect on Pulsar Timing 1. Dispersion measure variation What we will do: PSR B 0458+46 Calculate DM change for PPTA pulsars, improve the accuracy of pulsar timing Method: Obtain DM from simultaneous multi-frequency observation From Hobbs et al. (2004)

ISM Effect on Pulsar Timing 2. Scintillation effect • Scintillation affects precision of pulsar timing • Second dynamic spectrum can deduce the time delay PSR B 1737+13 What we will do: Study scintillation effect on PPTA pulsars, improve the accuracy of pulsar timing From Stinebring & Hemberger (2005)

Summary • Gravitational wave detection is a major goal for current astronomy • PPTA project has a chance for directly detecting gravitational wave • Lots of works still need to be done to improve the accuracy of pulsar timing