Review of basic concepts about AGNs

This lecture is part of the course "physics of active galactic nuclei" offered to graduate students in astrophysics by Rodrigo Nemmen and Joao Steiner at IAG USP.

https://rodrigonemmen.com/teaching/active-galactic-nuclei/

Transcript

2. Rodrigo Nemmen Radiative Processes: Review of Basic Concepts AGA5727 - Active Galactic Nuclei Credit: ESO
3. cosmic rays Fermi High-energy Astrophysics Gemini Swift Chandra HST VLA ALMA* SOAR GMT E-ELT LLAMA CTA neutrinos gravitational waves?
5. Ghisellini Difference between intensity and flux
6. Ghisellini Difference between intensity and flux Difference between intensity and flux Intensity: measure of irradiated energy along a light ray (directional)
7. Ghisellini Difference between intensity and flux Difference between intensity and flux you see each element of the surface under a different angle θ
8. t: Basics 5 ch e is gle al ⃗ n sees disk Ghisellini Difference between intensity and flux inside the shell. to F nsity I and the total flux F must account for the fact t of the surface is seen under a different angle θ. See sider the projected area, and introduce a cos θ term in F = I cosθdΩ (1.15)
9. Example of optically thin source R/⌧⌫
10. Example of optically thick source R/⌧⌫
11. 8 1 Some Fundamental Definitions Fig. 1.4 A layer of total optical depth τν ≫ 1 is observed face-on (left) and from an angle θ from its normal (right). The two observers receive always the emission produced in the shell of unit optical depth. But an optical depth of unity corresponds to the length AB (left) or CD (right). The two lengths are equal (AB = CD), but one is inclined, therefore the two volumes are different (by the factor DH/AB = cosθ) Ghisellini At an inclined angle of observation, the emitting volume is less by a cosθ factor
12. Mean free path (for a photon) Average distance traveled by a photon without interacting Distance for which ⌧⌫ = 1 Path (for a photon) is the average distance ℓ traveled by a photon t corresponds to a distance for which τν = 1: τν = 1 → σνnℓν = 1 → ℓν = 1 nσν (1.44)
13. Coulomb collisions a.k.a. as interaction between two charges mediated by the Coulomb force Frank et al. q1, m1 q2, m2
14. Coulomb collisions a.k.a. as interaction between two charges mediated by the Coulomb force q1, m1 q2, m2 m2 m1
15. Frank et al. b
16. Electric field produced by an accelerated charge v
17. Electric field produced by an accelerated charge
18. 1.13 The Electric Field of a Moving Charge 19 Fig. 1.10 The electric field produced by a charge initially in uniform rectilinear motion that is suddenly stopped. At large distances, the electric field points to where the charge would be if it had not been stopped. At closer distances, the electric field had time to “adjust” and points to where the charge is. There is then a region of space where the electric field has to change direction. This Electric field produced by an accelerated charge Ghisellini
19. 1.13 The Electric Field of a Moving Charge 19 Fig. 1.10 The electric field produced by a charge initially in uniform rectilinear motion that is suddenly stopped. At large distances, the electric field points to where the charge would be if it had not been stopped. At closer distances, the electric field had time to “adjust” and points to where the charge is. There is then a region of space where the electric field has to change direction. This Electric field produced by an accelerated charge Ghisellini electromagnetic wave (radiation) c t Run Mathematica demonstration
20. http://www.tapir.caltech.edu/~teviet/Waves/empulse.html
21. Pattern of emitted radiation of accelerated charges Ghisellini f a Moving Charge 21 he ge el to
22. Pattern of emitted radiation of accelerated charges Ghisellini he ge el to hat the pattern of the emitted radiation has a maximum per-
23. Pattern of a dipole antenna http://commons.m.wikimedia.org/wiki/File:Felder_um_Dipol.jpg
24. Pattern of a dipole antenna http://commons.m.wikimedia.org/wiki/File:Felder_um_Dipol.jpg
25. Pattern of a dipole antenna http://commons.m.wikimedia.org/wiki/File:Felder_um_Dipol.jpg
26. Radiation pattern of oscillating dipole https://www.youtube.com/watch?v=Lx7LNVtQvTs
27. The world in the fast lane: Relativistic photographs and light curves
29. ! 1
30. Penrose, R. The apparent shape of a relativistically moving sphere. Proc. Camb. Philos. Soc. 55, 137 (1959) 
 Terrel, J. Invisibility of the Lorentz contraction. Phys. Rev. 116, 1041 (1959) 
 We figured out apparent shapes of relativistic objects >50 years after special relativity was published
31. The moving bar A B Non-relativistic projected length: ✓ l0 sin ✓ l0
32. The moving bar A B ✓
33. The moving bar A B ✓ te actual observed length
34. Observed timescales and frequencies from relativistic sources A Lamp remains on for B ✓ t0 e Non-relativistic case: te = t0 e
35. Observed timescales and frequencies from relativistic sources A Lamp remains on for B ✓ t0 e Δt between arrival of first and last photon?
36. The relativistically moving square C D A B l0
37. The relativistically moving square 3 Beaming orresponding to Γ = √ 2 and to CB = ℓ′ √ 2, Note that we have considered the square (and Ghisellini cos ↵ =
38. Relativistic aberration and beaming
39. John Walker
40. John Walker
41. John Walker
42. John Walker
43. http://people.physics.anu.edu.au/~cms130/TEE/site/tee/learning/aberration/aberration.html Relativistic aberration in frame S'
44. http://www.fourmilab.ch/cship/aberration.html Relativistic aberration in three dimensions
45. http://math.ucr.edu/home/baez/physics/Relativity/SR/Spaceship/spaceship.html Relativistic aberration in interstellar travel
46. http://math.ucr.edu/home/baez/physics/Relativity/SR/Spaceship/spaceship.html Relativistic Doppler effect
47. http://math.ucr.edu/home/baez/physics/Relativity/SR/Spaceship/spaceship.html Relativistic aberration and Doppler effect in interstellar travel
48. Relativistic source radiating isotropically in its rest-frame: beaming based on http://math.ucr.edu/home/baez/physics/Relativity/SR/Spaceship/spaceship.html
50. Doppler factor δ4 as a function of viewing angle, for different values of Γ Ghisellini n I = 4I0 L = 4L0 for a single, relativistic blob
51. Moving in a homogeneous radiation field (i.e. relativistic blob moving in the BLR of a radio loud AGN) Ghisellini 3 Beaming hi, nice to meet you. I am relativistic blob escaping from a black hole
52. Moving in a homogeneous radiation field (i.e. relativistic blob moving in the BLR of a radio loud AGN) Ghisellini actor Γ . In the rest of the blob the oming from 90° in are seen to come at 1/Γ . The energy seen by the blob is by a factor ∼Γ 2 ll of broad line clouds. For simplicity, assume that the broad line photons uced by the surface of a sphere of radius R and that the jet is within it. As- so that the radiation is monochromatic at some frequency ν0 (in frame K). moving (in frame K′) observer will see photons coming from a cone of semi- 1/Γ (the other half may be hidden by the accretion disk): photons coming 3 Beaming S frame S’ frame U F U' F'
53. The first superluminal source detected in Our Galaxy Mirabel et al. 1994, Nature
55. Event Horizon Telescope Very Long Baseline Interferometry (VLBI)
56. Mirabel et al. 1994, Nature Source: GRS1915+105
59. Observed timescales and frequencies from relativistic sources A B ✓ C Blob shines for t0 e
60. Apparent velocity as a function of viewing angle, for different values of Γ Ghisellini 3 Beaming rent on of ction r the nel
61. Useful relativistic tranformations Ghisellini 3.4 A Question 45 Table 3.1 Useful relativistic transformations ν = ν′δ frequency t = t′/δ time V = V ′δ volume sinθ = sinθ′/δ sine cosθ = (cosθ′ + β)/(1 + β cosθ′) cosine I(ν) = δ3I′(ν′) specific intensity I = δ4I′ total intensity j(ν) = j′(ν′)δ2 specific emissivity κ(ν) = κ′(ν′)/δ absorption coefficient TB = T ′ B δ brightn. temp. (size directly measured) TB = T ′ B δ3 brightn. temp. (size from variability) U′ = (1 + β + β2/3)Γ 2U radiation energy density within an emisphere Dividing by ta = te(1 − β cosθ) we have the measured apparent velocity as βc t sinθ β sinθ