Introduction to Scintillation Arcs the single-dish version Dan - - PowerPoint PPT Presentation

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Introduction to Scintillation Arcs the single-dish version Dan - - PowerPoint PPT Presentation

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Introduction to Scintillation Arcs the single-dish version Dan Stinebring Oberlin College 2019 November 4 meta-comments international audience many non-native English speakers Im going to try to talk clearly and not

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Introduction to Scintillation Arcs
 – the single-dish version


Dan Stinebring Oberlin College 2019 November 4

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meta-comments

  • international audience — many non-native

English speakers — I’m going to try to talk clearly and not too fast

  • (I’ll try) to use full names in referring to

people

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Outline

  • Basic Ideas
  • More Advanced Ideas
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Outline

  • Basic Ideas
  • More Advanced Ideas Concepts
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SLIDE 5

Outline

  • Basic Ideas
  • More Advanced Ideas Concepts

Interference Effects

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Graphic: Aditya Parthasarathy (Swinburne Univ.)

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

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parabola eqn on data plot

fν

Cordes, Shannon, & Stinebring 2016

distributed

deterministic relation between angle of arrival and differential Doppler

  • nly a statistical relation

between angle of arrival and differential Doppler

all angles highly exagerrated! screen or shell

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1133+16 dyn & sec

linear grayscale

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1133+16 dyn & sec

logarithmic grayscale linear grayscale

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1133+16 dyn & sec

logarithmic grayscale linear grayscale

Dynamic spectrum is real so the
 secondary spectrum is reflection symmetric about the

  • rigin

—> just plot one half plane (usually)

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1133+16 dyn & sec

ν

t

fν

ft

logarithmic grayscale linear grayscale

dynamic (or primary) spectrum secondary spectrum

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1133+16 dyn & sec

ν

t

fν

ft

logarithmic grayscale linear grayscale

dynamic (or primary) spectrum secondary spectrum

<-Doppler-> <-Delay->

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1133+16 dyn & sec

ν

t

fν

ft

logarithmic grayscale linear grayscale

dynamic (or primary) spectrum secondary spectrum

(milliHertz) (microseconds)

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

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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!

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Dana Simard PhD thesis,
 Chapter 2

Some basic geometry (the screen location parameter “s”)

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Dana Simard PhD thesis,
 Chapter 2

Some basic geometry Observer moves (x) and the path length (ΔL) changes by a lot less 
 (order θ ≈ 1 mas 
 ≈ 10–9 less)

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Dana Simard PhD thesis,
 Chapter 2

Thin screen geometry How arclets are formed 1 (also, see 
 Mark Walker’s 2004 paper!)

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Dana Simard PhD thesis,
 Chapter 2

Thin screen geometry How arclets are formed 1 (also, see 
 Mark Walker’s 2004 paper!)

past future —>

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Dana Simard PhD thesis,
 Chapter 2

Thin screen geometry How arclets are formed 1 (also, see 
 Mark Walker’s 2004 paper!)

past

(ray getting longer with time)

future —>

(ray getting shorter with time)

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SLIDE 22

1133+16 dyn & sec

Hill, A.S., Stinebring, D.R., et al. 2005, ApJ,619, L171

these arclets were in the past

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Dana Simard PhD thesis,
 Chapter 2

Thin screen geometry How arclets are formed 2 (also, see 
 Mark Walker’s 2004 paper!)

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fν

ft

Walker et al. 2004

1d “image” on the sky

where do the arclets come from ?”

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

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Dana Simard PhD thesis,
 Chapter 2

A canonical form of differential delay

τ

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Dana Simard PhD thesis,
 Chapter 2

A canonical form of differential delay

Note that is not
 wavelength dependent

τ

τ

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Dana Simard PhD thesis,
 Chapter 2

A canonical form of differential Doppler

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Dana Simard PhD thesis,
 Chapter 2

A canonical form of differential Doppler

Note reversal

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

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Dana Simard PhD thesis,
 Chapter 2

A canonical form of the parabolic curvature

τ = η f2

D

(SI units: )

s3

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Outline

  • Basic Ideas
  • More Advanced Ideas Concepts
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Precision Scintillometry

Measure changes in arc curvature to infer geometry

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Precision Scintillometry

Measure changes in arc curvature to infer geometry

an under-used technique!

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1929+10 velocity plot

s = 0.39 s = 0.38 s = 0.37

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Daniel Reardon (Swinburne, OzGrav)

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Reardon, PhD thesis, 2018 pulsar around WD Earth around Sun

13 years of scint arc curvature measurements

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Reardon, PhD thesis, 2018 pulsar around WD Earth around Sun distance to the pulsar J0437-4715 distance to the primary screen

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Precision Scintillometry

Multiple arcs —> multiple screens

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PSR 1133+16

η = Dλ2 s(1− s) 2cVeff

2

Veff = (1− s)Dµpsr + sVobs − Vscreen

proper motion (2d) s=0 s=1

fν = η ft2

note: Veff differs from Simard definition. Use hers!

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1980 2005 2015 log curvature value (min2/MHz) 1 2 3 4 ≈ 4600 AU ≈ 0.02 pc Four arcs constant in curvature over 35 years!

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1980 2005 2015 log curvature value (min2/MHz) Four arcs constant in curvature over 35 years! 1 2 3 4 ≈ 4600 AU ≈ 0.02 pc

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1980 2005 2015 log curvature value (min2/MHz) Four arcs constant in curvature over 35 years! 1 2 3 4 ≈ 4600 AU ≈ 0.02 pc

N.B. tilt angle can move screens toward the pulsar

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toward Zeta Ophiuci (HII shell)

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NASA WISE (infrared image)

Image credit: NASA/JPL-Caltech/UCLA

24 km/s (bow shock)

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Preamble to conjecture:

all (or almost all) of the Kolmogorov ray tracing simulations you’ve seen assume a single thin screen along the LOS

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Conjecture:

rays scattered by a distributed Kolmogorov medium do not produce pronounced scintillation arcs

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  • A. Jussila 2018

Oberlin honors thesis rays random walk in a distributed medium

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The statistical connection between delay and Doppler (in this case) is a selection effect. It’s real, but it needs further quantitative exploration to see what sort of scintillation arcs it produces, if any.

Cordes, Shannon, & Stinebring 2016

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B0628–28 DM = 34 pc cm-3 distance = 320 pc

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B0628–28 DM = 34 pc cm-3 distance = 320 pc

distributed scattering

Conjecture

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B0628–28 DM = 34 pc cm-3 distance = 320 pc

but it’s not there!

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Don’t forget the Brisken arclets!

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Brisken dyn + secondary

1.2

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

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Mark Walker holography!

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dynamic delay - Doppler Walker et al. 2008 B0834+06 holographic modeling - Walker

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Delay τ Doppler ω Walker et al. 2008

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Delay τ Doppler ω

Walker et al. 2008

Wavefield representation 
 (no conjugate image)

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Time variable “illumination”

  • f scintillation arcs …
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Tilted 0355a

Roger Foster, GB 140 ft

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Tilted 0355b

Roger Foster, GB 140 ft

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Tilted 0919a

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Tilted 0919b

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6 µs 90 µs

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Hemberger and Stinebring 2008

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Hemberger and Stinebring 2008

B1737+13

DM = 48.7 pc cm-3

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delay = 2.2 µs delay = 0.2 µs

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delay = 2.2 µs delay = 0.2 µs 7 weeks

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delay = 2.2 µs delay = 0.2 µs 7 weeks smaller scintles bigger image (ray bundle) longer delay bigger scintles smaller image (ray bundle) shorter delay

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But, what’s a “scintle” in this dynamic spectrum?

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Delay (µs) à

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Delay (µs) à

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large “scintle” structure in the dynamic spectrum is power near the origin in the secondary spectrum

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Delay (µs) à

25 50

the fine scale cross-hatching in the dynamic spectrum produces the thin outer arc

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Dana Simard PhD thesis,
 Chapter 2

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Dana Simard PhD thesis,
 Chapter 2 Fundamental Theorem of Radio Interferometry … sky brightness <— FT —> visibility

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Concluding Comments

  • (even) single-dish scintillation studies

are yielding surprises and new insights

  • there are many unexplored or under-

explored lines of inquiry

  • we are learning how to “read the tea

leaves” of scintillation arcs