Gravitational wave detection using radio pulsar timing

Fredrick A Jenet

CGWA/UTB

Collaborators

Dick ManchesterATNF/CSIRO

Australia

George HobbsATNF/CSIRO

Australia

KJ LeePeking U.

China

Andrea LommenFranklin & Marshall

USA

Shane L. LarsonPenn State

USA

Linqing WenAEI

Germany

Teviet CreightonJPLUSA

John ArmstrongJPLUSA

Main Points of This Talk• Radio Pulsars can be used to detect

gravitational waves (G-waves).– Current use is limited– Efforts are underway to increase the sensitivity of such a

“detector”– Sensitive to nano-Hertz G-waves– Primary Signal: G-waves from Super Massive Black Hole

Binaries

• Limits can be placed with a single pulsar.– The mass of the proposed binary system in 3C 66B

• An array of pulsars are needed to positively detect G-waves.– Most likely signal: A stochastic background generated by super

massive black holes distributed throughout the universe.– Parkes Pulsar Timing Array: A US-Australian collaboration to

detect the stochastic background

What can we do with an array of pulsars and the G-wave

background?

1. Make a definitive detection of G-waves.

2. Measure the polarization properties of the G-waves.

3. Place limits on the graviton mass.

4. Study the properties of the G-wave source.

What are Gravitational Waves?

“Ripples in the fabric of space-time itself”

g = + h

h / t + 2 h = 4 T

G (g) = 8 T

What is a Radio Pulsar?

• Radio Pulsars are neutron stars that emit regular bursts of radio radiation.

What is pulsar timing?

Pulsar timing is the process of measuring the time-of arrival (TOA) of each individual pulse and then subtracting off the expected time-of-arrival given a physical model of the system.

What is pulsar timing?

1) Observe a pulsar and measure the Time Of Arrival (TOA) of each pulse.

Time

Inte

nsit

y

What is pulsar timing?

2) Determine a TOA model which best fits the TOA data.

Pulse Number

TO

A

TOAm = P £ N + T0

What is pulsar timing?

2) Determine a TOA model which best fits the TOA data.

In General TOAm includes the effects of:1. Telescope motion

1. Earth’s rotation2. Earth’s orbit

2. Pulsar Motion1. Binary companion2. Proper motion3. Planets

What is pulsar timing?

3) Calculate the timing “Residual”

R = TOA – TOAm

All the interesting physics is in the residuals

If we know everything about the pulsar, R = 0

Timing residuals from PSR B1855+09

From Jenet, Lommen, Larson, & Wen, ApJ , May, 2004

Data from Kaspi et al. 1994

The effect of G-waves on pulsar timing

Earth

Pulsar

k

Photon Path

G-wave

Pulsar Earth

The effect of G-waves on pulsar timing

h = R Rrms 1 s h >= 1 s /N1/2

10-14

10-13

10-12

3 10-9

h

Frequency, Hz

3 10-8 3 10-7

10-15

10-16

3 10-103 10-11

Sensitivity of a Pulsar timing “Detector”

*3C 66B 1010 Msun BBH

@ a distance of 20 Mpc

109 Msun BBH@ a distance of 20 Mpc

SMBH Background

*OJ287

Upper Limits vs Detection

• A single pulsar can place upper limits on the existence of G-waves.

• An array of pulsars is necessary to make a definitive detection.

Orbital Motion in the Radio Galaxy 3C 66B: Evidence for a Supermassive Black Hole Binary Hiroshi Sudou,1* Satoru Iguchi,2 Yasuhiro Murata,3 Yoshiaki Taniguchi1

Supermassive black hole binaries may exist in the centers of active galactic nuclei such as quasars and radio galaxies, and mergers between galaxies may result in the formation of supermassive binaries during the course of galactic evolution. Using the very-long-baseline interferometer, we imaged the radio galaxy 3C 66B at radio frequencies and found that the unresolved radio core of 3C 66B shows well-defined elliptical motions with a period of 1.05 ± 0.03 years, which provides a direct detection of a supermassive black hole binary.

Volume 300, Number 5623, Issue of 23 May 2003, pp. 1263-1265. Copyright © 2003 by The American Association for the Advancement of Science. All rights reserved.

Upper Limit Case Study:3C66B

Sudou et al.’s adopted parameters for 3C 66B

• Mt = 5.4 1010 Msolar

• Mass ratio = .1

• Mchirp = 1.3 1010 Msolar

• Orbital period = 1.05 .03 yrs

• Distance = 85 Mpc (H=75 km/s/Mpc)

• h Mchirp5/3 / D 10-12

• R = h/ = 3 s

From Jenet, Lommen, Larson, & Wen, ApJ May 10th 2004

The expected signature of G-waves from 3C66B on PSRB1855+09

Here and Now There and Then

The observed residuals contain a component that depends on what the binary system was doing 3000 years ago!

Constraints on 3C66B

– The parameters adopted by Sudou et al. can be ruled out with 98% confidence.

– Mchirp < 0.7 1010 Msolar assuming e < 0.01.

The most likely source of G-waves that pulsars will detect will be a stochastic background generated by super-massive binary black

holes distributed throughout the universe!

• Jaffe & Backer (2002)

• Wyithe & Lobe (2002)

• Enoki, Inoue, Nagashima, Sugiyama (2004)

Like the cosmic micro-wave background, the G-wave background is an incoherent sum of G-waves.

hc = A f-

= 2/3

A = 10 -15 to 10 -14 yrs-2/3

The Stochastic Background

For a single plane wave:

For more then one plane wave:

The measured timing residuals:

The timing residuals for a stochastic background

This is the same for all pulsars.

This depends on the pulsar.

The induced residuals for different pulsars will be correlated.

The Expected Correlation Function

Assuming the G-wave background is isotropic:

The Expected Correlation Function

How to detect the Background

How to detect the Background

Single Pulsar Limit(1 s, 7 years)

1 s, 1 year(Current ability)

Expected Regime

.1 s5 years

.1 s10 years

SKA10 ns5 years40 pulsars

hc = A f-2/3

Detection SNR for a given level of the SMBH background Using 20 pulsars

The Parkes Pulsar Timing Array

• US-Australian Collaboration– ATNF,Swinburne, UTB, Carleton College

• Goal: 20 Pulsars, 100 nano-second RMS, 10 years.

Current Status of the PPTA

• Collecting data for 2 years

• 4 pulsars with RMS < 500 ns.– Best: J1909-3744 with RMS = 200 ns

• 8 pulsars with RMS < 1 s

• Systematic effects are being studied

• New Hardware recently comissioned

h = R Rrms 1 s h >= 1 s /N1/2

10-14

10-13

10-12

3 10-9

h

Frequency, Hz

3 10-8 3 10-7

10-15

10-16

3 10-103 10-11

Sensitivity of a Pulsar timing “Detector”

*3C 66B 1010 Msun BBH

@ a distance of 20 Mpc

109 Msun BBH@ a distance of 20 Mpc

SMBH Background

*OJ287

Summary• Pulsar timing observations may be used to detect the presence

of G-waves– R h/ > 200 ns– Use is limited by the current timing noise levels

• Limits can be placed with single pulsars.– Using existing timing data, constraints are placed on the

parameters of the proposed SBBH in 3C66B– The Sudou et al. system is ruled out at the 98% level– Assuming near zero eccentricity, Mc < 0.7 1010 Msolar

– See Jenet, Lommen, Larson, and Wen ApJ, May 2004 • Multiple pulsars are needed for a positive detection.

– Detection of the Stochastic Background– PPTA :20 pulsars, 100 ns, 5 years -> 3-5 sigma detection – SKA : 40 pulsars, 10 ns, 5 years -> > 10 sigma detection– Jenet, Hobbs, Lee, Manchester ApJ Letters, May 2005

(astro ph # 0504458)

Summary