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Astroparticle physics with high-energy photons I – The physics

Astroparticle physics with high-energy photons I – The physics. Alessandro de Angelis Lisboa 2003. http://wwwinfo.cern.ch/~deangeli. The starting point. Physics constructs models explaining Nature (or better our observations of Nature, or better observations of our interactions with Nature)

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Astroparticle physics with high-energy photons I – The physics

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  1. Astroparticle physicswith high-energy photonsI – The physics Alessandro de Angelis Lisboa 2003 http://wwwinfo.cern.ch/~deangeli

  2. The starting point • Physics constructs models explaining Nature (or better our observations of Nature, or better observations of our interactions with Nature) • We know Nature mostly through our eyes, which are sensitive to a narrow band of wavelengths centered on the emission wavelength of the Sun

  3. We see only partly what surrounds us • We see only a narrow band of colors, from red to purple in the rainbow • Also the colors we don’t see have names familiar to us: we listen to the radio, we heat food in the microwave, we take pictures of our bones through X-rays…

  4. What about the rest ? • What could happen if we would see only, say, green color?

  5. The universe we don’t see • When we take a picture we capture light (a telescope image comes as well from visible light) • In the same way we can map into false colors the image from a “X-ray telescope” • Elaborating the information is crucial

  6. We know there is something important we don’t see velocity v radius r Gravity: G M(r) / r2 = v2 / r enclosed mass: M(r) = v2 r / G Luminous stars only small fraction of mass of galaxy

  7. Many sources radiate over a wide range of wavelengths

  8. The high-energy spectrum Eg > 30 keV (l ~ 0.4 A, n ~ 7 109 GHz) Although arbitrary, this limit reflects astrophysical and experimental facts: • Thermal emission -> nonthermal emission • Problems to concentrate photons (-> telescopes radically different from larger wavelengths) • Large background from cosmic particles

  9. And that things can look different

  10. The subject of these lectures…(definition of terms) • Detection of high-energy photons from space • High-E X/g: probably the most interesting part of the spectrum for astroparticle • What are X and gamma rays ? Arbitrary ! (Weekles 1988) X 1 keV-1 MeV X/low E g 1 MeV-10 MeV medium 10-30 MeV HE 30 MeV-30 GeV VHE 30 GeV-30 TeV UHE 30 TeV-30 PeV EHE above 30 PeV No upper limit, apart from low flux (at 30 PeV, we expect ~ 1 g/km2/day)

  11. Outline of these lectures 0) Introduction & definition of terms 1) Motivations for the study high-energy photons 2) Historical milestones 3) X/g detection and some of the present & past detectors 4) Future detectors

  12. 1) Motivations for the study of X/g • Probe the most energetic phenomena occurring in nature • Nonthermal • Nuclear de-excitation/disintegration • Electron interactions w/ matter, magnetic & photon fields • Matter/antimatter ann. • Decay of unstable particles • Clear signatures from new physics

  13. Motivations (cont’d) Penetrating • No deflection from magnetic fields, point ~ to the sources • Magnetic field in the galaxy: ~ 1mG R (pc) = 0.01p (TeV) / B (mG) => for p of 300 PeV @ GC the directional information is lost • Large mean free path • Regions otherwise opaque can be transparent to X/g • Good detection efficiency

  14. Large mean free path…Transparency of the Universe

  15. Astronomy Scales Nearest Stars Nearest Galaxies Nearest Galaxy Clusters 4.5 pc 450 kpc 150 Mpc 1 pc= 3 light years

  16. ‘GZK cutoff’ HE cosmic rays Interaction with background ( infrared and 2.7K CMBR) p   N Sources uniform in universe 100 Mpc HE gamma rays 10 Mpc Mrk 501 120Mpc    e+ e Milky Way Mrk 421 120Mpc

  17. Transparency of the atmosphere

  18. PHYSICS GOALS • Pulsars • GRBs • AGNs • SNRs • New VHM particles • Anomalous events • -ray Backg. • Cold Dark Matter • Photon propagation- Invariance of c

  19. Acceleration mechanisms and the origin of cosmic rays • Energetic protons and electrons in the vicinity of astrophysical objects might produce gammas • Synchrotron radiation by electrons in magnetic fields could be boosted to TeV energies by inverse Compton scattering • If acceleration mechanisms involve hadronic interactions, there are many p0 -> gg (& the g give a clear signature)

  20. Active galaxies • Many sources, mostly classified according to observational criteria • Unified AGN model (Begelman et al. 1984): 10% of the accreted mass is transformed into radiation • Different models predict different g spectra But warning : ~300 sources @ the GeV scale, only 15 @ the TeV

  21. Crab pulsar X-ray image (Chandra) Pulsars • Rapidly rotating neutron stars with • T between ~1ms and ~1s • Strong magnetic fields (~100 MT) • Mass ~ 3 solar masses • R ~ 10 Km (densest stable object known) • For the pulsars emitting TeV gammas, such an emission is unpulsed

  22. g-ray bursts (History, I) • An intriguing puzzle of today’s astronomy… A brief history • Beginning of the ‘60s: Soviets are ahead in the space war • 1959: USSR sends a satellite to impact on the moon • 1961: USSR sends in space the 27-years old Yuri Gagarin • 1963: the US Air Force launches the 2 Vela satellites to spy if the Soviets are doing nuclear tests in space or on the moon • Equipped with NaI (Tl) scintillators

  23. g-ray bursts (History, II) • 1967 : an anomalous emission of X and g rays is observed. For a few seconds, it outshines all the g sources in the Universe put together. Then it disappears completely. Another in 1969... After careful studies (!), origination from Soviet experiments is ruled out • The bursts don’t come from the vicinity of the Earth • 1973 (!) : The observation is reported to the world • Now we have seen hundreds of gamma ray bursts...

  24. g-ray bursts: why they are important • They might represent objects near the edge of the observable Universe • The energy could be 1015 times larger than the energy from a supernova • E ~ 1045 J • They could be a new observational tool for cosmologist

  25. g-ray bursts: what we knowand what we’d like to know • They come from every direction in the sky • Mostly extragalactic • Frequently no optical emission (BeppoSAX 1997) • Far away from the galaxy • A puzzle… • Time duration is wildly variable • Afterglows after > 1h… • Several mechanisms proposed, enormous energies: a great chance that they’re so far...

  26. Importance of the multiwavelength approach

  27. A recent consensus • Many sources can be related to SN remnants • Mechanism accounting for repeated shocks (Dar, De Rujula) • Matter of precise poninting: Work for GLAST • Synergy with gravitational wave detectors Work for LIGO • But: Maybe different kinds of bursts…

  28. Probability of bursts • Present estimate: 1 GRB/100My/Milky Way Galaxy => Already ~ 100 GRB in our galaxy • Energy ~ 1045 J • According to Dar, it is not unlikely that a GRB has already interacted with the atmosphere…

  29. Diffuse background radiation • Is it really diffuse (<- produced at a very early epoch) or a flux from unresolved sources ? • Angular resolution is the key

  30. Physics in extreme conditions: photon propagation • Due to gg -> e+e-, CMB and visible light absorb g at the PeV and at the TeV • At the GKZ cutoff (1020 eV) the Universe regains transparency to g The transparency of the Universe gives insights on the infrared/ optical diffuse background • Quantum gravity (Amelino-Camelia et al., Ellis et al.) V = c (1 - e E/EQG) Effects on GRB could be O(100 ms)

  31. => Intergalactic g absorption • Photons interact with the IR background => relationship source distance / maximum observed photon energy • Measurement from the distortion of AGN spectra • Data in the range 50 GeV - 300 GeV would be crucial • And an important byproduct: the best constraints on Lorentz violation, photon oscillations etc.

  32. Particle physics at high energies • Today’s accelerator physics limited & many early discoveries in particle physics came from the study of cosmic rays • Motivation for particle physicists to join

  33. LHC CERN, Geneva, 2007 Particle Physics  Particle Astrophysics Energy of accelerated particles Active Galactic Nuclei Binary Systems SuperNova Remnant Diameter of collider Cyclotron Berkeley 1937

  34. DM Candidates M > ~ 40 GeV if SUSY (LEP)

  35. q X or  or Z q X Probing dark matter: WIMPs Some dark matter candidates (e.g. SUSY particles) would lead to mono-energetic g lines through annihilation

  36. Anomalous events • Anomalous showers at UHE (> 7 PeV) from Cygnus X-3 (Samorski & al. 1983): almost no photons… • Increasing total photon X-section due to virtual gluons • Increasing neutrino X-section • New particles • Anomalous events (highly penetrating hadrons) • Normally killed as “irreproducible results”, but…

  37. Study of exotic objects: other phenomena • Top-Down : Decay of massive cosmic strings (1015 GeV, Kolb & Turner 1990) • Unknown transients • Time resolution is the key

  38. 2) Historical milestones 1952 Prediction of He X/g high energy emission (Hayakawa) 1957 Sputnik 1 1958 Inventory of cosmic sites expected to radiate in the X/g (Morrison) 1968 (11 years after the Sputnik): X emission of the galaxy 1972 g from Crab Nebula 1973 First report on gamma ray bursts 1978 Gamma-ray spectroscopy : e+e- annihilations @ the GC 1983 Nuclear processes at the GC

  39. Some selected results

  40. X/g Satellites in the ’90s • GRANAT (SIGMA), 1990/97 • Accreting black holes • Jets • CGRO, 1991/2000 • BATSE, thousands of GRB • EGRET, hundreds of GRB in the HE region • BEPPO Sax, 1996/2002 • SN remnants

  41. Gamma satellites • EGRET [+BATSE] • Diffuse g emissions dominate the g-ray sky. After removing the identified point sources, ~ mass distribution • Moreover, isotropic emission at high latitude going like E-2.07+-0.03 • Pulsars, all observed also in the radio (apart from Geminga) • Most point sources unidentified • Gamma-Ray Bursts, not expected in any model. No apparent E cut-off, E as high as 18 GeV The pulsar spectrum depends on the wavelength => Different energies produced in different regions

  42. Results from ground-based

  43. VHE sources • Observations in the ‘90s confirm earlier detection of VHE emissions from Crab nebula and discover new VHE sources in pulsars (PSR 1706-44, Vela) • No pulsed emission • TeV emission from AGN, with flares • Mkr 421 • Mkr 501 Models differ in the kind of particles emitted & E spectrum • Synchrotron model => 2 humps, one from synchrotron and one from inverse Compton • Variability over a large range of timescales Observational hole upper limit from EGRET

  44. UHE (and EHE ?) • No sources of UHE g (only diffuse emission) • No signal from established VHE g sources • No signals from hypothetical new sources (primordial black holes, black holes accreting from a nearby star…) • Although the GRB spectrum from BATSE/EGRET is hard (E-2), no UHE g seen (and they would be expected…) • Absorption in the em field ? Detection problems ?

  45. Comment on VHE and UHE gammas • Ground-based astronomy operates in regimes of large background => results are matter of discussions • VHE emissions from Crab and Vela are accepted as genuine • No episodic emission widely accepted yet • Many astronomical models of AGN suffer from lack of information in the ~50 GeV region… • Fill the hole • No relevant information for particle physics, yet • Relevant is what should have been observed, but has not • TeV gammas from SN shocks should have been seen • Correlation between EGRET objects, TeV emissions and SNR ?

  46. The progress at a glance

  47. Sensitivity

  48. Summary • High energy photons (often traveling through large distances) are a great probe of physics under extreme conditions • What better than a crash test to break a theory ? • Observation of X/g rays gives an exciting view of the HE universe • Many sources, often unknown • Diffuse emission • Gamma Ray Bursts • No clear sources above ~ 30 TeV • Do they exist or is this just a technological limit ? • We are just starting… Next lecture: many new detectors being built or planned Future detectors: have observational capabilities to give SURPRISES !

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