White - Welcome to Superluminal Phase-Wave Civilization (2003)
Introduction to Extra-galactic Radio Sources & Apparent Superluminal motion
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Transcript of Introduction to Extra-galactic Radio Sources & Apparent Superluminal motion
Introduction to Extra-galactic Radio Sources & Apparent Superluminal motion
Anupreeta MoreMy sincere thanks to Dr. Saikia (NCRA, Pune)
Contents
● Features of an Extra-galactic radio source● Fanaroff-Riley Classification● Apparent Superluminal motion & its explanation● Relativistic Beaming● Summary
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
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
FRI FRII 3C272.1 3C47
3C465 3C83.1B 3C296 1.4 GHz 1.38 GHz 1.5GHz
Images of FRI sources
Images of FRII sources
VLBI maps of 3C273A second look
C
Observer
c t
v t v t cos
c t-v t cos
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 )
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
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 )
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
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