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

Introduction to Scintillation Arcs 
 – the single-dish version 
 Dan Stinebring Oberlin College 2019 November 4

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

Outline • Basic Ideas • More Advanced Ideas

Outline • Basic Ideas • More Advanced Ideas Concepts

Interference Effects Outline • Basic Ideas • More Advanced Ideas Concepts

Graphic: Aditya Parthasarathy (Swinburne Univ.)

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

all angles highly exagerrated! parabola eqn on data plot f ν distributed screen or shell only a statistical relation deterministic relation between angle of between angle of arrival and arrival and differential Doppler differential Doppler Cordes, Shannon, & Stinebring 2016

1133+16 dyn & sec linear grayscale

1133+16 dyn & sec linear grayscale logarithmic grayscale

1133+16 dyn & sec linear grayscale Dynamic spectrum is real so the 
 secondary spectrum is reflection symmetric about the origin logarithmic grayscale —> just plot one half plane (usually)

dynamic (or primary ) spectrum 1133+16 dyn & sec linear grayscale ν t secondary spectrum f ν logarithmic grayscale f t

dynamic (or primary ) spectrum 1133+16 dyn & sec linear grayscale ν t secondary spectrum f ν <-Delay-> logarithmic grayscale <-Doppler-> f t

dynamic (or primary ) spectrum 1133+16 dyn & sec linear grayscale ν t (microseconds) secondary spectrum f ν logarithmic grayscale (milliHertz) f t

“ 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!

Some basic geometry (the screen location parameter “s”) Dana Simard PhD thesis, 
 Chapter 2

Some basic geometry Observer moves (x) and the path length ( Δ L) changes by a lot less 
 (order θ ≈ 1 mas 
 ≈ 10 –9 less) Dana Simard PhD thesis, 
 Chapter 2

Thin screen geometry How arclets are formed 1 (also, see 
 Mark Walker’s 2004 paper!) Dana Simard PhD thesis, 
 Chapter 2

Thin screen geometry How arclets are formed 1 past future —> (also, see 
 Mark Walker’s 2004 paper!) Dana Simard PhD thesis, 
 Chapter 2

Thin screen geometry How arclets are formed 1 past future —> (also, see 
 (ray getting (ray getting longer with shorter with Mark Walker’s time) time) 2004 paper!) Dana Simard PhD thesis, 
 Chapter 2

1133+16 dyn & sec Hill, A.S., Stinebring, D.R., et al. 2005, ApJ,619, L171 these arclets were in the past

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

Where do the “arclets” (inverted parabolas) where do the arclets come from ? ” come from? 1d “image” on the sky f ν f t Walker et al. 2004

A canonical form of differential delay τ Dana Simard PhD thesis, 
 Chapter 2

A canonical form of differential delay Note that is not 
 τ wavelength dependent τ Dana Simard PhD thesis, 
 Chapter 2

A canonical form of differential Doppler Dana Simard PhD thesis, 
 Chapter 2

A canonical form of differential Doppler Note reversal of j, k indices Dana Simard PhD thesis, 
 Chapter 2

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

A canonical form of the parabolic curvature τ = η f 2 D s 3 (SI units: ) Dana Simard PhD thesis, 
 Chapter 2

Outline • Basic Ideas • More Advanced Ideas Concepts

Precision Scintillometry Measure changes in arc curvature to infer geometry

Precision Scintillometry Measure changes in arc curvature to infer geometry an under-used technique!

1929+10 velocity plot s = 0.39 s = 0.38 s = 0.37

Daniel Reardon (Swinburne, OzGrav)

13 years of scint arc curvature measurements pulsar around WD Earth around Sun Reardon, PhD thesis, 2018

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

Precision Scintillometry Multiple arcs —> multiple screens

PSR 1133+16 η = D λ 2 s (1 − s ) 2 2 cV eff s=0 s=1 V eff = (1 − s ) D µ psr + s V obs − V screen proper motion (2d) note: Veff differs from Simard definition. Use hers! f ν = η f t2

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

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

Four arcs constant in curvature over 35 years ! 4 log curvature value (min 2 /MHz) ≈ 4600 AU ≈ 0.02 pc 3 2 N.B. tilt angle can move screens toward the pulsar 1 1980 2005 2015

toward Zeta Ophiuci (HII shell)

24 km/s (bow shock) NASA WISE (infrared image) Image credit: NASA/JPL-Caltech/UCLA

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

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

rays random walk in a distributed medium A. Jussila 2018 Oberlin honors thesis

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

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

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

B0628–28 DM = 34 pc cm -3 distance = 320 pc but it’s not there!

Don’t forget the Brisken arclets!

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

Mark Walker holography!

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

Delay τ Doppler ω Walker et al. 2008

Delay τ Doppler ω Wavefield representation 
 (no conjugate image) Walker et al. 2008

Time variable “illumination” of scintillation arcs …

Tilted 0355a Roger Foster, GB 140 ft

Tilted 0355b Roger Foster, GB 140 ft

Tilted 0919a

Tilted 0919b

6 µ s 90 µ s

Hemberger and Stinebring 2008

B1737+13 DM = 48.7 pc cm -3 Hemberger and Stinebring 2008

delay = 2.2 µ s delay = 0.2 µ s

7 weeks delay = 2.2 µ s delay = 0.2 µ s

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

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

Delay ( µ s) à

50 large “scintle” structure in the dynamic spectrum is power near the origin in the secondary spectrum Delay ( µ s) à 25

50 the fine scale cross-hatching in the dynamic spectrum produces the thin outer arc Delay ( µ s) à 25

Dana Simard PhD thesis, 
 Chapter 2

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

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