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Introduction and Overview

Introduction and Overview. X-ray/Gamma-ray Astronomy. The Great Observatories. Chandra. High Energy Astrophysics Sample Sources Professor George F. Smoot Extreme Universe Lab, SINP Moscow State University. Great Observatories. Opacity of Atmosphere. Versus characteristic temperature.

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Introduction and Overview

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  1. Introduction and Overview X-ray/Gamma-ray Astronomy. The Great Observatories. Chandra. High Energy Astrophysics Sample Sources Professor George F. Smoot Extreme Universe Lab, SINP Moscow State University

  2. Great Observatories

  3. Opacity of Atmosphere

  4. Versus characteristic temperature

  5. characteristic temperature

  6. characteristic temperature

  7. Chandra

  8. X-ray Producing Collision

  9. Synchrotron Radiation

  10. Inverse Compton Scattering

  11. Atomic Emission

  12. Birth of an X-ray

  13. Chandra: Revolution through Resolution Martin Elvis, Chandra X-ray Center

  14. The Chandra X-ray Observatory Launched 23 July 1999 revolutionized X-ray astronomy, and all of astronomy. What is X-ray Astronomy? What is Chandra? Why has Chandra done its job so well? And what exactly has Chandra done?

  15. When we look up at the night skywe see it filled with stars What is X-ray Astronomy? Outside the narrow range of colors our eyes are sensitive to, something quite different dominates the night sky…

  16. Powerful sources of X-rays X-ray map of the whole sky: 100,000 `sources’ Rosat All Sky Survey (MPE) A power source entirely different from the nuclear fusion that drives the Sun and stars …and much more efficient X-ray Astronomy tries to find out what could cause such extraordinary power

  17. X-ray Astronomy studies short wavelength light from the Universe 1/1000 1015 range of wavelength in astronomymillion billion between shortest & longest Whipple 10 meter Compton gamma-ray Observatory X-rays 1/1000 Chandra Hubble Visible MMT Sub-millimeter array VLA

  18. Compare Visible light and X-rays:“1000 times” X-rays have: • Wavelengths: 1/1000 visible light • 0.1-6 nm (1-60A) vs. 500 nm (5000A) • Energies: 1000 x visible light • “keV” instead of “eV” (electron volts) • About 0.02 Joules/photon • Temperatures: 1000 times hotter • 10 million degrees vs. 10 thousand degrees for stars • E=kT (k= Boltzman’s constant, 1.398x10-9 J/K) SNR G292.0+1.8 (Hughes et al.)

  19. What gets so hot? • Surely not much can get so hot as a million degrees? • Oh yes it can… Explosions: Supernovae and their remnants Particles moving near the speed of light in magnetic fields Matter falling into deep gravitational wells Supernova 1987a Crab Nebula Abell 2029 Cluster of galaxies Andromeda nearest galaxy ¼ sun – a centauri sun sun a centauri Sounds obscure but … gravity power is the most common source of X-rays in thesky

  20. 40 Years of X-ray Astronomy:1 billion times more sensitive Sco X-1: the brightest source of X-rays in the sky 1962 Good for 1 (one) Nobel Prize 2001 Chandra good enough for my thesis 1978 Distant galaxy 100,000 times fainter than NGC3783 Moon to scale 1999 NGC3783: a quasar appearing 10,000 times fainter than Sco X-1 Resolution is the key

  21. X-ray astronomy took just 40 years to match 400 years of optical astronomy Chandra takes X-ray Astronomy from its ‘Galileo’ era to its ‘Hubble’ era in a single leap 0.1” Hubble Space Telescope Galileo 1” Optical Astronomy 10” Chandra X-ray Astronomy Sharpest Detail detectable 100” Dawn of History 1600 1700 1800 1900 2000 Year

  22. What is Chandra? Chandra is the greatest X-ray Observatory ever built Orbits the Earth to be above the atmosphere (which absorbs X-rays, luckily!) Goes 1/3 of the way to the Moon every 64 hours (22/3 days) Chandra takes superbly sharp images: ‘high resolution imaging’

  23. Chandra’s mirrors are almost cylinders X-rays don’t reflect off a normal mirror – they get absorbed. Only by striking a mirror at a glancing angle, about 1o, do X-rays reflect. Then they act like visible light and can be focused X-ray Telescopes are different This makes for looooooooong telescopes

  24. Chandra is as big as a moving truck 10 meters (32 ft) from mirror to detector, 1.2 meters (4ft) across mirror …but focuses X-rays onto a spot only 0.025mm (1/1000 inch) across That’s why Chandra is powerful

  25. Chandra detects individual photons Uses Wave-Particle Duality of Light CCD detectors count each X-ray individually each X-ray knocks free enough electrons to detect as a pulse of electricity Light as particles …but can disperse the incoming X-ray light: Light as Waves Delicate gold gratings diffract the light Chandra provides a great example of how Quantum wave/particle duality works in a real machine

  26. Chandra’s sharp focus revolutionizes our understanding Earth observing satellite equivalents of … SPACE IMAGING Best X-ray image of whole sky (ROSAT) Best X-ray images before Chandra (ROSAT) Chandra images Any sign of life? What’s this odd thing? I get it!

  27. Like looking up the answers at the back of the book Chandra has solved 20 year old mysteries in just one shot: Yes – the background X-ray light is made up of contributions from millions of quasars No – gas is not pouring down onto the galaxy at the center of a cluster of galaxies. Something stops it, but what? Yes -- Our Milky Way sits in a bath of hot gas stretching to the Andromeda galaxy and beyond Yes – quasars have hot winds blowing from their cores, at 2 million miles per hour

  28. Antennae – colliding galaxies Nest of super-bright black holes in binaries – bigger than any star? …but also being given a whole new SAT test, without taking the class 2 examples: What are we looking at? Centaurus A – nearest quasar X-ray ‘smoke ring’ from explosion in core?

  29. Antennae: Deep Exposure Chandra’s Revolution through Resolution continues… • Chandra set to run for 5 more years • & may last much longer • Deeper looks show • more and more detail, • more and more surprises

  30. High Energy Astrophysics • • • High energy astrophysics typically deals with x-rays and higher energy radiation. It also deals with high energy neutrinos and other particles such as protons, electrons, positrons etc. • • • High energy radiation is produced by objects at high temperatures and/or relativistic particles. • 1 ev = 10,000 K, 1 kev = 107 K • • This usually requires compact objects such as white dwarfs, neutron stars or blackholes with deep gravitational potential. Vesc=(2GM/R)1/2 approaching c • Or R not much greater than the Schwarzschild radius: 2 GM/c2 (2.95 km for a solar mass object).

  31. Roentgenhistoric X-ray

  32. X-ray astronomy: 0.1 to 100 kevGamma-ray astronomy: >100 kev. E=hn= k T ==> x-rays probe 106 -- 109 K and gamma-rays > 109 K Eddington Luminosity: 1.3x1038 erg/s for 1 Mo. (derive the Eddington limit) Optically thick blackbody radiation in x-ray requires a compact object! T as a function of object mass, radius (in units of Schwarzschild radius) and Luminosity (in units of Eddington luminosity), is given by: T ~ 7 kev (L/L_Edd)^{1/4} (R/R_s)^{-1/2} (M/M_sun)^{-1/4} Thus if the radiation is black-body and luminosity is close to Eddington, Then x-ray temperature is reached provided that R\sim R_s and M is not much greater than M_sun. This result is violated, as it often is, when the radiation is non-thermal.

  33. Brief Property and History of Compact Objects 1. 1914: Adams-- Sirius B has M~ 1Mo, T~ 8000 K, R~10,000km 2. 1925: Adams confirmed M & R by measuring gravitational redshift -- z ~ GM/(R c2)=0.0003. 3. 1926: F-D statistics discovered. Fowler applied it to model WDs. 4. 1930: Chandrasekhar: WD model including relativity; mass limit. 5. 1983: Nobel prize to Chandrasekhar. White dwarfs: R~10,000 km, Vesc~0.02 c, density~ 106 g/cc (Nuclear reaction is more efficient source of energy than the PE release of in-falling gas on WDs).

  34. Neutron Stars 1. 1931: Chadwick --discovers neutrons. 2. 1934:Baade & Zwicky suggested neutron-stars, and postulated their formation in supernovae. 3. 1967: Hewish, Bell et al. Discover radio pulsars. 4. 1968: Gold proposed rotating NS model. 5. 1974: Nobel prize to Ryle (aperture synthesis) Hewish (pulsars). 6. 1975: Hulse & Taylor discover binary pulsar PSR 1913-16. 7. 1993: Nobel prize to Hulse & Taylor. Neutron stars: R~15 km, Vesc~0.32 c, density~ 1014 g/cc (Nuclear reaction is much less efficient source of energy than the PE release of in-falling gas on NSs - gravitation).

  35. Black Holes 1795: Laplace noted the possibility of light not being able to escape. 1915: Einstein’s theory of general relativity. 1916: Schwarzschild -- metric for a spherical object 1963: Kerr --metric for a spinning BH. 1972: Discovery of Cyg X-1 1995: Miyoshi et al. -- NGC 4258. 1997: Eckart & Genzel -- (Sgr A*) Galactic center. Schwarzschild radius = 2.95 km M/Mo Efficiency of energy production 6% to 42%. 2002: Nobel prize in physics to Giacconi (x-ray astronomy).

  36. Summary 1. Derivation of the Eddington limit. 2. We found that bright sources of high energy photons are typically compact objects such as WD, NS or BH. High speed, strong, shocks are another way of generating high energy photons; however high speed shocks are usually produced when compact objects form eg. SNe, GRB etc. (an exception is x-rays from clusters.)

  37. Atmospheric Transmission (1 Ao = 12.5 kev)

  38. Eary All Skly Catalog

  39. EUV picture of the Sun at 171 A = 74 ev (SOHO) EUV picture of the Sun at 171 A = 74 ev (SOHO) Coronal luminosity: ~ 1026 erg/s Corona & several Active regions are visible

  40. EUV picture of the Sun at 195 A = 65 ev from SOHO Corona, active regions and a flare are visible

  41. Sun approaching Solar Max at 195 A = 65 ev

  42. Accretion to create X-ray binary

  43. An artist’s view

  44. Crab Pulsar Crab nebula (Plerion) Blue: x-ray Red: optica Green:radio Luminosity ~ 1038 erg/s (mostly x-ray & gamma) Synchrotron radiation: (linear polarization of 9% averaged over nebula). Electrons with energy > 1014 ev are needed for emission at 10 kev; lifetime for these e’s < 1 year. So electrons must be injected continuously & not come from SNe.

  45. Crab redux Plerion: is derived from the Greek word “pleres” which means “full”. Crab nebula is the remnant of Sne explosion (perhaps type II) observed by the Chinese Astronomers in 1054 (July 4th). The pulsar at the center has a period of 33milli-sec. Crab shows pulsed emission from radio to optical to >50 Mev! Moreover, The pulse shape is nearly the same over this entire EM spectrum, suggesting A common origin for the radition which is believed to be synchrotron (curvature radiation). The radio is produced not too far away from the Neutron star (within 5-10 radii) and high energy pulsed radiation is Likely produced near the light cylinder. The bolometric luminosity is pulsed radiation is about a factor 100 smaller Than nebular radiation; pulsed radio is smaller than total pulsed radiation By a factor of 10^4.

  46. SN remnant: Cas A (3-70 kev; Chandra) Plerion SNe II remnant Age 300 yr (1670 AD) X-ray luminosity: 3.8x1036 erg/s Mass of x-ray gas 10-15 solar mass.

  47. Pulsar wind nebula G292(Chandra 3-80 kev) (Plerion)

  48. SN remnant G11.2-0.3 in x-ray (Chandra) X-ray luminosity: ~ 1036 erg/s. The radiation is produced by shock heated gas at ~ 109 K via bremsstrahlung. Note the bright (blue) Pulsar nebula at the Center. Produced in SN of 386 AD

  49. Gamma-ray burst: note the relativistic jet, and supernova explosion

  50. AGN jet from the quasar GB 1508+5714 (distance 4Gpc) Chandra x-ray obs. Obs. jet size~30 kpc (x-ray produced by IC of CMB-photons with jet e-s)

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