Multiwavelength astronomy is extreme astronomy!

1. Multiwavelength astronomy is extreme astronomy! OUTLINE Importance of Multiwavelength Astronomy Some Basics A Picture of our Universe How Images are Made How Photons are Made In particular, Gamma Rays Image isn’t Everything Spectral and Time domain information The Blazar Example Lucy Fortson - Extreme Astronomy Short Course

2. Importance of Multiwavelength astronomy • No astrophysical object emits photons at a single wavelength. • Some objects have many photon producing and changing mechanisms going on at once • Need multiwavelength astronomy to piece together whole picture • Because we can’t always see all wavelengths, we use other wavelengths to detect objects. Lucy Fortson Extreme Astronomy Short Course

3. What does the em-spectrum tell us? • Transports energy • Electric and magnetic fields oscillate: that’s the “wave” • Moves at speed of light, 3 x 108 m/s • Wavelength, frequency, energy all related • Type of radiation (usually) depends on energy/temperature of object Lucy Fortson Extreme Astronomy Short Course

4. Putting it into perspective

5. Atmospheric effects • Only visible, most radio and some infra-red gets through air! • To see Gamma-ray, X-ray, UV and some IR, need to get above atmosphere. • Can indirectly “see” gamma-rays from ground through airshowers. Lucy Fortson Extreme Astronomy Short Course

6. A Picture of our universe • There’s a lot happening in the photon universe - in spite of Dark Matter and Dark Energy • From the objects in our Solar System to the furthest quasar and even the Big Bang itself, photons are emitted, scattered, absorbed and otherwise mangled on their way to us. • Let’s take a brief tour… Lucy Fortson Extreme Astronomy Short Course

7. Moon Galaxy Heliosphere GRB IGM Mag Field Stellar BH GCBH Earth Planets ISM IPM Nebula AGN Supernova Solar wind Sun Photons

8. Moon Visible UV Infra-red X-ray Radio

9. Sun Visible EUV X-ray Radio IR

10. X-ray Jupiter Visible Infrared Radio Saturn

11. Interplanetary Medium • Dust • Gas • Magnetic Fields • Cosmic Rays

12. Open cluster: Pleiades - M45 at 380 ly radio x-ray visible ultra violet near IR

13. Planetary Nebula Dumbbell - M27 at 1250 ly x-ray Radio Far IR visible near IR

14. Emission Nebula (M17 - Omega Nebula) 5000 light years away in Sagittarius x-ray radio mid-IR far IR near IR

15. UV Crab Nebula M1 - 6300 ly in Taurus Gamma-ray X-ray Radio Visible Radio, Visible, X-ray

16. visible Multi-wavelength Milkyway low x-ray short radio ultraviolet long radio infrared x-ray gamma sources gamma-ray

17. Andromeda Galaxy M31 - 2.9 mil ly ultraviolet mid-IR visible radio x-ray

18. X-Ray Centaurus A 10 mil ly UV Vis: Hubble Vis: Ground Mid IR Near IR Radio Gamma Ray

19. More than just a pretty picture • An “image” is made up of pixels containing number of photons received by a detector • depends on sensitive range of detector • may be combinations of two or three “filters” • color is usually artificially determined Hubble site example • Comparing images of an object in different wavelengths can tell us about the many processes going on. Lucy Fortson Extreme Astronomy Short Course

20. The peculiar Centaurus A • This peculiar galaxy resulted from merging an elliptical and spiral galaxy • Colors tell us: • blue - new stars • red - old stars • black - dust lanes Lucy Fortson Extreme Astronomy Short Course

21. Timelapse images of Supernova 1987a • Comparing visible, x-ray and radio shows radical changes. • Supernova blast wave reaches surrounding material • X-ray, radio images show where real hotspots are: • radio confirms high energy electrons in mag field • x-ray indicates temperatures of blast millions of degrees Lucy Fortson Extreme Astronomy Short Course

22. A little isn’t enough • In some cases, images are made because that is what is expected. • Each “new” wavelength goes thru phase of low statistics and/or low resolution. • TeV gamma ray astronomy has come of age with new detectors - useful images! HESS images Crab Nebula SNR RXJ1713 Lucy Fortson Extreme Astronomy Short Course

23. Image isn’t everything • Images only tell part of the story • After all, x-ray and gamma-ray astronomy has told us lots before we got to the point where we could make an “image”. • Plot parameters of photons to understand the information behind the image: • intensity versus energy (spectrum) • intensity versus time (light curve) • But to understand all this - we need to know how photons are made! Lucy Fortson Extreme Astronomy Short Course

24. How photons are made or modified • Thermal Radiation • Nuclear, atomic or molecular excitations • (absorption, emission lines) • Acceleration or de-acceleration of charged particles • Elementary particle decay • Scattering (gain or lose energy) Lucy Fortson Extreme Astronomy Short Course

25. Thermal radiation • Anything above absolute zero emits EM radiation • Stars, gas, planets, YOU! • “Blackbody Radiation” • The hotter an object the higher the intensity • The hotter an object the higher frequency the peak emission. Lucy Fortson Extreme Astronomy Short Course

26. Emission and absorption effects • A spectrum may be modified by medium it passes through • Thermal spectrum of Sun from photosphere is modified: • by its chemical elements to produce absorption lines • by the corona (hot plasma) to produce emission lines Lucy Fortson Extreme Astronomy Short Course

27. Extreme effects from extreme astronomy • The high energy world invades the imagination • The Hulk created by gamma rays • Fantastic Four gain powers by exposure to cosmic rays Lucy Fortson Extreme Astronomy Short Course

28. How Gamma-rays are made • Gamma-rays are emitted through four basic processes: • Transitions between nuclear energy levels (line emission) • Annihilation of particles with antiparticles (line emission) • Decays of elementary particles (broad band emission) • neutral pion decay is major player in gamma ray astronomy • Acceleration of charged particles • Bremsstrahlung - field around nucleus • Synchrotron - static magnetic field • Compton scattering - EM field of photon Lucy Fortson Extreme Astronomy Short Course

29. High Energy emission mechanisms (1) • Bremsstrahlung - “breaking radiation” • Radiation is emitted when charged particles accelerate in the field of an ion Lucy Fortson Extreme Astronomy Short Course

30. high energy emission mechanisms (2) • Synchrotron - “ magnetic spin radiation” • Caused by a relativistic electron as it spirals around a magnetic field line • Non-relativistic version is called cyclotron radiation Lucy Fortson Extreme Astronomy Short Course

31. high energy emission mechanisms (3) • Compton Scattering - “rebound radiation” • A high-energy photon hits a low-energy electron. The photon loses energy, and the electron gains some. • Inverse Compton Scattering: A low-energy photon hits a relativistic electron. The photon gains energy, becoming an X- or gamma-ray. Lucy Fortson Extreme Astronomy Short Course

32. The spectral keys • Supernova remnant Cas A observed in gamma rays • What emission mechanism is at work? • Dotted line • neutral pion decay • Dashed line • Bremsstrahlung and Compton, B=1.6 mG • Solid line • Brem + Compton, B=1 mG Lucy Fortson Extreme Astronomy Short Course

33. Time domain • Multiwavelength light curves of seven pulsars seen in HE gammas • measure intensity versus time • pulsars repeat, so build up peaks Lucy Fortson Extreme Astronomy Short Course

34. The multiwavelength story of AG(N) • Active galaxies have very high luminosities • large amount of star formation • accretion driven jets • Multiwavelength analysis helps figure out which is which: • Arp 220 versus Centaurus A Lucy Fortson Extreme Astronomy Short Course

35. Active Galactic Nuclei (3c219 courtesy NRAO/HST) • Giant elliptical galaxies • Black hole at center • Relativistic jets, accretion power Lucy Fortson Extreme Astronomy Short Course

36. Active galaxy’s Shocking blobs • Jets of M87 • knots of material ejected out of central core propagate down the jet • seen side on • What happens when jet is aimed at Earth? • Blazar! • beamed gamma ray and x-ray emission Lucy Fortson Extreme Astronomy Short Course

37. blazar Light Curves • Building up data from different wavelengths over time • variability seen on minutes, days, years • correlations in flares between wavelengths Lucy Fortson Extreme Astronomy Short Course

38. Mrk 501 spectral energy distribution • Correlation in variability between synchrotron and g-ray emission naturally explained by IC: • Same population of electrons produce both components. • g-Ray measurements provide separate constraint on electron energy, breaks degeneracies. Lucy Fortson Extreme Astronomy Short Course

39. Blazar Emission Mechanisms • Current paradigm: • Synchrotron Self Compton • External Compton • Proton Induced Cascades • Proton Synchrotron • Energetics, mechanism for jet formation and collimation, nature of the plasma, and particle acceleration mechanisms are still poorly understood Lucy Fortson Extreme Astronomy Short Course (Buckley, Science, 1998)

40. AGNs: The Central Engine? • More than phenomenological understanding of radiative processes • VHE g-rays provide probes of strong gravity close to the central engine Lucy Fortson Extreme Astronomy Short Course

41. Summary • Multiwavelength astronomy is relatively new • radio since 1950’s, x-ray, gamma-ray since 1970’s • Just learning the best ways to utilize MWL as tool • coordination amongst different astronomy cultures • targets of opportunity • merging data archives from different groups • time-domain (building lightcurves) is resource intensive • MWL is extreme because it pulls together all the information we have on different objects: MWL WILL DOMINATE THE FUTURE OF ASTRONOMY Lucy Fortson Extreme Astronomy Short Course