The Extreme Dimension: Time-Variability and The Smallest ISM Scales

The Extreme Dimension: Time-Variability and

The Smallest ISM Scales

Dan StinebringOberlin College

Some key collaborators

• Jim Cordes• Barney Rickett, Bill Coles (UCSD)

• Maura McLaughlin (discovery paper)

• Oberlin college students ...

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

1133+16 dyn & sec

logarithmicgrayscale

lineargrayscale

1133+16 dyn & sec

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ν

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t

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fν

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ft

logarithmicgrayscale

lineargrayscale

dynamic (or primary) spectrum

secondary spectrum

Coherent radiation scatters off electron inhomogeneities

~ 1 kpc

~ 10 mas

Multi-path interference causesa random diffraction pattern

Relative transverse velocities produce a dynamic spectrum

time

Scattering in a thin screen plusa simple core/halo model canexplain the basics ofscintillation arcs

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

~ 1 kpc

~ 1 – 10 mas

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

The substructure persists

and MOVES!

Arecibo observations

January 2005

QuickTime™ and aPhoto - JPEG decompressor

are needed to see this picture.

Hill, A.S., Stinebring, D.R., et al.

2005, ApJ,619, L171

This is the angular velocity of the pulsar across the sky! 51 ± 2 mas/yr

Brisken dyn + secondary

1.2

Walter Brisken (NRAO) et al.“Small Ionized and NeutralStructures,” Socorro, NM, 2006 May 23

B1737+13 movie• Ira asked about the anisotropy of the turbulence ...

Cumulative Delay - Arclets

time delays scale as

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τ ∝ν−3.6Kolmogorov:

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τ ∝ν−4.4

Arecibo is the best!

•Raw sensitivity is essential

•Excellent instrumentation•Some bands (e.g. 327 MHz) have low RFI

•(small, focused projects are the key ...)

A new result ...

• 6 months of ~ weekly Arecibo observations of a moderate DM pulsar (B1737+13)

• 4 x 50 MHz bands near 21 cm• Investigate time variability of ScintArc structure and its effect on pulsar timing

How Does this Work?

conjugate time axisConjugate time axis (heuristic)

d

D

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θ =d

D

y

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y =λ

d

⎛

⎝ ⎜

⎞

⎠ ⎟D

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ft =1

Pt=Vxθ xλ€

=λθ

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Pt =y

V=λ

Vθ

V

incident plane wave (λ)

conjugate freq axisConjugate frequency axis (heuristic)

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fν =1

Pν=πDθ 2

c

D€

Dθ 2

2

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θ

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Pν =δν =c

πDθ 2

incident plane wave (λ)

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δt =Dθ 2

2c

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2π δt δν =1

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δν

where do the parabolas come from ?”

Where do the parabolas come from?

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fν =πDθ 2

c

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ft =Vθ

λ

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fν = ±πDλ2

cV 2

⎛

⎝ ⎜

⎞

⎠ ⎟ ft

2

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ft€

fν

parabola eqn on data plotB2021+25

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fν

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ft€

fν ∝ ft2

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fν

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ft Walker et al. 2004

1d “image” on the sky

where do the arclets come from ?”

Where do the “arclets” (inverted parabolas) come from?

Some ObservationalHighlights ...

The Earth Orbits the Sun !!

Effective Velocity

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Veff⊥ =(1−s)Vp⊥+sVobs⊥−Vscr⊥

Cordes and Rickett 1998, ApJ, 507, 846

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s ≡Dpsr−screen

Dtotal

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η=λ2D s (1− s)

2cVeff2

1929+10 velocity plot

Multiple Arcs —>

Multiple “Screens”

“Screen” Locations

fν = η ft

2

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η=λ2D s (1− s)

2cVeff2

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Veff⊥ =(1−s)Vp⊥+sVobs⊥−Vscr⊥

PSR 1133+16

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η=Dλ2 s(1− s)

2cVeff2

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Veff = (1− s)Dμ psr + sVobs − Vscreen

proper motion (2d)

s=0 s=1

fν = η ft

2

Can We Improve High-accuracyPulsar Timing?

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)

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 B1855+09


Cumulative Delay - No Arclets

1133+16 dyn & sec

D. Hemberger

B1737+13 tau_ss + errors (36 epochs)

D. Hemberger

Summary• Interstellar scattering allows us to probe the ISM on AU-size scales.

• Much of the scattering appears to be localized in thin “screens” along the line of sight. We don’t know what these screens are.

• There is evidence for compact (~ AU), dense (~ 100 cm-3) structures of unknown origin.

• Scattering effects are time variable and need to be corrected for in highest precision pulsar timing.

• LOFAR is an excellent telescope with which to pursue these studies!!

Dan StinebringOberlin [email protected]

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)


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 B1855+09


Want to achieve < 1 us residuals for 10 pulsarsfor 5 years

Name DM RMS Residual (us)J0437-4715 2.65 0.12J1744-1134 3.14 0.65J2124-3358 4.62 2.00J1024-0719 6.49 1.20J2145-0750 9.00 1.44J1730-2304 9.61 1.82J1022+1001 10.25 1.11J1909-3744 10.39 0.22J1857+0943 13.31 2.09J1713+0747 15.99 0.19J0711-6830 18.41 1.56J2129-5721 31.85 0.91J1603-7202 38.05 1.34J0613-0200 38.78 0.83J1600-3053 52.19 0.35J1732-5049 56.84 2.40J1045-4509 58.15 1.44J1643-1224 62.41 2.10J1939+2134 71.04 0.17J1824-2452 119.86 0.88

R. N. Manchester Sept 2006

Timing Behavior vs. Dispersion Measure

0.00

0.50

1.00

1.50

2.00

2.50

3.00

0.00 20.00 40.00 60.00 80.00 100.00 120.00 140.00

DM (pc cm^-3)

Timing RMS (microseconds)

data: R. N. Manchester

What we measure ...

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y(t) = I (t)∗h(t)ISM impulse response function

ISM

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Rh (τ ) = h(t) h(t − τ ) dt∫the autocorrelation of the impulse response

At the moment, we use the centroid of

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Rh (τ )

€

h(t)

A new result ...

• 6 months of ~ weekly Arecibo observations of a moderate DM pulsar (B1737+13)

• 4 x 50 MHz bands near 21 cm• Investigate time variability of ScintArc structure and its effect on pulsar timing

B1737+13 secondary spectrum

movie

1133+16 dyn & sec

D. Hemberger

Timing Residuals (Observed – Model) for PSR B1855+09

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

psr distance(kpc) V (km/s) sB0823+26 0.38 196 0.36B0834+06 0.72 174 0.33B0919+06 1.2 505 0.59B1133+16 0.27 475 0.49

Roger Foster, GB 140 ft

Tilted 0355b


Roger Foster, GB 140 ft

Tilted 0919a


Tilted 0919b


The Gravitational Wave Spectrum


Sky Distribution of Millisecond PulsarsP < 20 ms and not in globular clusters


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The Extreme Dimension: Time-Variability and The Smallest ISM Scales

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