introduction to extra-galactic radio sources & apparent superluminal motion
DESCRIPTION
Anupreeta More My sincere thanks to Dr. Saikia (NCRA, Pune). Introduction to Extra-galactic Radio Sources & Apparent Superluminal motion. Contents. Features of an Extra-galactic radio source Fanaroff-Riley Classification Apparent Superluminal motion & its explanation Relativistic Beaming - PowerPoint PPT PresentationTRANSCRIPT
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Introduction to Extra-galactic Radio Sources & Apparent Superluminal motion
Anupreeta MoreMy sincere thanks to Dr. Saikia (NCRA, Pune)
![Page 2: Introduction to Extra-galactic Radio Sources & Apparent Superluminal motion](https://reader035.vdocuments.mx/reader035/viewer/2022062305/56814d5c550346895dba9ad0/html5/thumbnails/2.jpg)
Contents
● Features of an Extra-galactic radio source● Fanaroff-Riley Classification● Apparent Superluminal motion & its explanation● Relativistic Beaming● Summary
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Features of an Extragalactic Radio source
A) Core ~ mas B) Jets ~ pc-kpc
C) Hotspots ~ kpc D) Lobes – (lobe to lobe) ~ 100 kpc
A
C
B
D
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Fanaroff-Riley ClassificationR = dist. between brightest regions
total extent of the sourceL(178 MHz) ~ 2x1025 W/Hz/rad2
Class FRI Class FRII
● jet dominated● turbulent, subsonic jets● weaker total radio power● associated with large cD
galaxies located in rich clusters
● hotspot & lobe dominated
● collimated, supersonic jets
● stronger total radio power
● associated with more isolated large galaxies
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FRI FRII 3C272.1 3C47
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3C465 3C83.1B 3C296 1.4 GHz 1.38 GHz 1.5GHz
Images of FRI sources
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Images of FRII sources
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VLBI maps of 3C273A second look
C
Observer
c t
v t v t cos
c t-v t cos
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Explanation of apparent superluminal motion
After time t,
distance covered along the line of sight: v t cos ө transverse distance covered : v t sin ө delayed time as seen by the observer : t (1- cos ө )
Hence for the observer,the apparent transverse velocity is
vapp = v t sin ө / t (1- cos ө )
app = sin ө / (1- cos ө )
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A) For a fixed value of ,
at = cos i.e. ~1/
app(max) =
Lorentz factor
> 0.707 app > 1
i.e apparent superluminal motion
B) For a fixed value of app ,
at cot-1app
min app / (1 + app2)1/2
minapp
2
As increases , increases as --> 1
max = 2 cot-1app
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Relativistic Beaming
For an object moving relativistically at a small angle to the line of sight to the observer, we find the flux to be enhanced which is called Relativistic Beaming
For a spherically symmetric source with a power law spectrum, F() I() & F()
the observed flux is boosted by
Fobs() = D Frest()
where D = 1 / (1 – cos )
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The ratio of observed flux of a relativistically
moving blob approaching at an angle to the
one receding ( is given by,
Fapp = (1 + cos )
Frec (1 – cos )
Fapp
Frec
Observer
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Summary
1. FRI & FRII sources may be intrinsically different or have different host galaxy environments
2. Orientation effects and Relativistic Beaming - explain SL motion & one-sided jets respectively - help in building unified models