Searching for Gravitational Waves with Millisecond Pulsars: Dan Stinebring Oberlin College CWRU – May 21, 2009

George Greenstein (Amherst College)

Discovery of “Millisecond” Pulsars 1982 – Arecibo Observatory – Don Backer, Sri Kulkarni,... Spun-up by accretion in a binary system 10 8 – years old (compared to 10 6 – 10 7 ) Timing precision < 1  s is possible in many cases (as opposed to ≈ 1 ms)

Millisecond Pulsar Spin-up

B The Vela pulsar The first millisecond pulsar (1982, Backer & Kulkarni)

Arecibo Observatory – the world’s largest radio telescope

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Sky Distribution of Millisecond Pulsars P < 20 ms and not in globular clusters R. N. Manchester (ATNF)

space What is a gravitational wave? A 2-D analogy motion in this dimension is meaningless 2 free masses The masses track each other with lasers Ron Hellings (Montana SU)

The gravitational wave is a wave of curvature each slice is a section of an arc of constant radius Ron Hellings (Montana SU)

the free masses remain fixed at their coordinate points As a gravitational wave passes through the space... while the distance between them Ron Hellings (Montana SU)

increases due to the extra space in the curvature wave. The laser signal has to cover more distance and is delayed Ron Hellings (Montana SU)

Why are gravitational waves called “a strain in space”? points that are close have little space injected between them points that are further away have more space injected between them Ron Hellings (Montana SU)

Black slide [Markus Pössel, AEI

Black slide [Markus Pössel, AEI

Black slide [Markus Pössel, AEI

Detecting Gravitational Waves with Pulsars Observe the arrival times of pulsars with sub-microsecond precision. Correct for known effects (spin-down, position, proper motion,...) through a multi-parameter Model Fit. Look at the residuals (Observed - Model) for evidence of correlated timing noise between pulsars in different parts of the sky. Timing residuals for PSR B Arecibo data

Black slide R. N. Manchester

Black slide Correlation Expected between Pulsars in Different Directions F. Jenet (UTB)

Fact of Life #1 The gravitational effect is due only to what happens at the two ends of the path: h(t then, x psr ) – h(t now, x Earth )

Fact of Life #2 Fitting for unknown pulsar parameters removes power from the data: (P, dP/dt, position, angular motion, binary orbit,...) Blandford, Narayan, and Romani 1984

Anne Archibald, McGill University Zaven Arzoumanian, Goddard Space Flight Center Don Backer, University of California, Berkeley Paul Demorest, National Radio Astronomy Observatory Rob Ferdman, CNRS, France Paulo Freire, NAIC Marjorie Gonzalez, University of British Columbia Rick Jenet, University of Texas, Brownsville, CGWA Victoria Kaspi, McGill University Vlad Kondratiev, West Virginia University Joseph Lazio, Naval Research Laboratories Andrea Lommen, Franklin and Marshall College Duncan Lorimer, West Virginia University Ryan Lynch, University of Virginia Maura McLaughlin, West Virginia University David Nice, Bryn Mawr College Scott Ransom, National Radio Astronomy Observatory Ryan Shannon, Cornell University Ingrid Stairs, University of British Columbia Dan Stinebring, Oberlin College

The Gravitational Wave Spectrum Spectrum R. N. Manchester (ATNF)

Figure by Paul Demorest (see arXiv: )

Summary Pulsars are ideal for detecting the low frequency (nHz) end of the gravitational wave spectrum. This technique is complementary to the LIGO and LISA efforts. Arecibo is critical to detecting gravitational waves in the next decade. What is needed: more pulsars, more telescope time, reduction in systematics. Dan Stinebring Oberlin College

Bertotti, Carr, & Rees (1983) (1)

Bertotti, Carr, & Rees (1983)

Compact object inspiral

Bertotti, Carr, & Rees (1983)

Quadrupole Gravitational Waves a ring of free test masses h+h+ less space Ron Hellings (Montana SU) more space

Lorimer&Kramer (LK) Fig. 4.2 Sketch showing inhomogeneities in the ISM that result in observed scattering and scintillation effects.

dyn & sec logarithmic grayscale linear grayscale

dyn & sec logarithmic grayscale linear grayscale dynamic (or primary) spectrum secondary spectrum

Cumulative Delay - Arclets

Hemberger & Stinebring 2008, ApJ, 674, L37

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Pulsars are different from VIRGO, etc. The only h (t, x) that matters is h (t emission, x pulsar ) and h (t arrival, x Earth ). We don’t track the electromagnetic phase, but we do track the pulsar rotational phase (in the best cases to 100 ns resolution). Pulsars are located all over the sky. This is a GOOD thing because each pair is a separate detector.

LIGO: Laser Interferometer Gravitational-wave Observatory US NSF project Two sites: Washington State and Louisiana Two 4-km vacuum arms, forming a laser interferometer Sensitive to GW signals in the 10 – 500 Hz range Initial phase now commissioning, Advanced LIGO ~ 2011 Most probable astrophysical source: merger of double neutron- star binary systems R. N. Manchester (ATNF)

LISA: Laser Interferometer Space Antenna ESA – NASA project Orbits Sun, 20 o behind the Earth Three spacecraft in triangle, 5 million km each side Sensitive to GW signals in the range – Hz Planned launch ~2015 Most probable astrophysical sources: Compact stellar binary systems in our Galaxy and merger of binary black holes in cores of galaxies R. N. Manchester (ATNF)

Detection of Gravitational Waves Prediction of general relativity and other theories of gravity Generated by acceleration of massive object(s) (K. Thorne, T. Carnahan, LISA Gallery) Astrophysical sources:  Inflation era  Cosmic strings  Galaxy formation  Binary black holes in galaxies  Neutron-star formation in supernovae  Coalescing neutron-star binaries  Compact X-ray binaries (NASA GSFC) R. N. Manchester (ATNF)

What we can measure... ISM impulse response function the autocorrelation of the impulse response At the moment, we use the centroid of

Comparison of Dyn/Sec spectra

Cumulative Delay - No Arclets

dyn & sec D. Hemberger

B tau_ss + errors (36 epochs) D. Hemberger

Detecting Gravitational Waves with Pulsars Observed pulse periods affected by presence of gravitational waves in Galaxy (psr at time of emission; Earth at time of reception) For stochastic GW background, effects at pulsar and Earth are uncorrelated Use an array of pulsars to search for the GW background that is correlated because of its effect on the Earth (at time of reception) Best limits are obtained for GW frequencies ~ 1/T where T is length of data span Timing residuals for PSR B R. N. Manchester (ATNF) Want to achieve < 1 us residuals for 10 pulsars for 5 years

R. N. Manchester Sept 2006

data: R. N. Manchester

What we measure... ISM impulse response function ISM the autocorrelation of the impulse response At the moment, we use the centroid of

A new result... 6 months of ~ weekly Arecibo observations of a moderate DM pulsar (B ) 4 x 50 MHz bands near 21 cm Investigate time variability of ScintArc structure and its effect on pulsar timing

B secondary spectrum movie

dyn & sec D. Hemberger

dyn & sec D. Hemberger

Timing Residuals (Observed – Model) for PSR B

“Deflection of Pulsar Signal Reveals Compact Structures in the Galaxy, ” A. S. Hill et al. 2005, 619, L17

The substructure persists and MOVES! Hill, A.S., Stinebring, D.R., et al. 2005, ApJ,619, L171 This is the angular velocity of the pulsar across the sky!

Brisken dyn + secondary 1.2 Walter Brisken (NRAO) et al. “Small Ionized and Neutral Structures,” Socorro, NM, 2006 May 23

How Does this Work?

Coherent radiation scatters off electron inhomogeneities ~ 1 kpc ~ 10 mas

Multi-path interference causes a random diffraction pattern

Relative transverse velocities produce a dynamic spectrum time

Scattering in a thin screen plus a simple core/halo model can explain the basics of scintillation arcs

Time variability of scintillation arcs will allow probing of the ISM on AU size scales

Kolmogorov vs. Gaussian PSF How to produce a “core/halo” psf? A Gaussian psf will NOT work: No halo.

Kolmogorov vs. Gaussian PSF Kolmogorov turbulence DOES work It produces a psf with broad wings

conjugate time axis Conjugate time axis (heuristic) d D y V incident plane wave ( )

conjugate freq axis Conjugate frequency axis (heuristic) D incident plane wave ( )

where do the parabolas come from ?” Where do the parabolas come from?

parabola eqn on data plot B

Walker et al d “image” on the sky where do the arclets come from ?” Where do the “arclets” (inverted parabolas) come from?

Some Observational Highlights...

The Earth Orbits the Sun !!

Effective Velocity Cordes and Rickett 1998, ApJ, 507, 846

velocity plot

Multiple Arcs —> Multiple “Screens”

“Screen” Locations f =  f t 2

PSR proper motion (2d) s=0s=1 f =  f t 2

Summary Pulsars are ideal probes of the ionized ISM New phenomena to explore and learn to interpret Pulsars may detect gravitational waves before the expensive detectors! Larger more sensitive telescopes will provide breakthroughs! LOFAR, SKA... Thanks to: Sterrewacht Leiden & NWO

Scintillation Arcs Underlie Other Scintillation Patterns

Tilted 0355a Roger Foster, GB 140 ft

Tilted 0355b Roger Foster, GB 140 ft

Tilted 0919a

Tilted 0919b

The Gravitational Wave Spectrum R. N. Manchester (ATNF)

Sky Distribution of Millisecond Pulsars P < 20 ms and not in globular clusters R. N. Manchester (ATNF)

Black slide [Markus Pössel, AEI

Black slide [Markus Pössel, AEI

Discovery of “Millisecond” pulsars in 1982 changed everythingBlack slide Timing residuals for PSR B

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