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Introduction to Extra-galactic Radio Sources & Apparent Superluminal motion

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

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Introduction to Extra-galactic Radio Sources & Apparent Superluminal motion

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  1. Anupreeta More My sincere thanks to Dr. Saikia (NCRA, Pune) Introduction to Extra-galactic Radio Sources & Apparent Superluminal motion

  2. Contents • Features of an Extra-galactic radio source • Fanaroff-Riley Classification • Apparent Superluminal motion & its explanation • Relativistic Beaming • Summary

  3. Features of an Extragalactic Radio source C A) Core ~ mas B) Jets ~ pc-kpc C) Hotspots ~ kpc D) Lobes – (lobe to lobe) ~ 100 kpc D B A

  4. hotspot & lobe dominated collimated, supersonic jets stronger total radio power associated with more isolated large galaxies 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

  5. 3C272.1 3C47 FRI FRII

  6. Images of FRI sources 3C465 3C83.1B 3C296 1.4 GHz 1.38 GHz 1.5GHz

  7. Images of FRII sources

  8. A second look C q v t cos q v t c t c t-v t cos q Observer VLBI maps of 3C273

  9. 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- bcos ө ) Hence for the observer, the apparent transverse velocity is vapp = v t sin ө/t (1- bcos ө ) bapp = b sin ө/ (1- bcos ө ) Explanation of apparent superluminal motion

  10. B) For a fixed value of bapp , at q = cot-1bapp bmin = bapp / (1 + bapp2)1/2 gmin = (1 + bapp2)1/2 As b increases , q increases as b --> 1 qmax = 2 cot-1bapp A) For a fixed value of b , at b = cos q i.e. q ~1/g bapp(max) = g b g  Lorentz factor b > 0.707  bapp > 1 i.e apparent superluminal motion

  11. 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(n) a I(n) & F(n) an-a the observed flux is boosted by Fobs(n) = D3+a Frest(n) where D = 1 / g (1 – b cos q) Relativistic Beaming

  12. Frec q Fapp Observer • The ratio of observed flux of a relativistically • moving blob approaching at an angle q to the • one receding (q + p) is given by, • Fapp = (1 + b cos q) 3+a • Frec (1 – b cos q)

  13. 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 Summary

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