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.
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logarithmicgrayscale
lineargrayscale
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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
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⎝ ⎜
⎞
⎠ ⎟ 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
R. N. Manchester (ATNF)
Cumulative Delay - No Arclets
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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)
R. N. Manchester (ATNF)
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
R. N. Manchester (ATNF)
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 )
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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
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
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 0919a
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
Tilted 0919b
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
The Gravitational Wave Spectrum
R. N. Manchester (ATNF)
Sky Distribution of Millisecond PulsarsP < 20 ms and not in globular clusters
R. N. Manchester (ATNF)
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