Introduction to Cosmic Rays Dr. Johana Chirinos Michigan Tech University

1. Introduction to Cosmic Rays Dr. Johana Chirinos Michigan Tech University

2. Cosmic Rays Discovery by Hess in 1912. Cosmic rays: high energy particles incident on Earth from outer space, plus secondary particles, which they generate as they traverse atmosphere. Their study: pioneering role in study of elementary particles and their interactions. -Discovery in cosmic rays of antimatter: positron in 1932 -Discovery of πs and μs and strange particles in 1940s kick-started building of large particle accelerators and development of detection equipment: essential for elementary particle physics.

3. Cosmic Rays In 1990s: study of interactions of solar and atmospheric ν, on distance scales far larger than anything at accelerators or reactors, revealed first cracks in Standard Model: evidence for ν flavour mixing and for finite ν masses. This led to a revival, in the new millenium, of lepton physics in fixed-target experiments at accelerators, development of new proposals: building of μ storage rings to serve as sources of high energy νe and νμ. At highest energies, studies of γ-rays in TeV range and above indicated point sources in the skies where it seems the most violent events in the universe have taken place. Ιntensive studies of both γ-rays and ultra-high energy protons and heavier nuclei will shed new light on mechanisms for particle acceleration, as well as new fundamental processes at energies far in excess of what could ever be achieved on Earth.

4. The spectrum and composition of cosmic rays Charged primary particles: - protons (86%) - α-particles(ll%) - nuclei of heavier elements up to uranium (1%), - electrons (2%). Αlso very small proportions of positrons and antiprotons, of secondary origin, generated by interactions of primary particles with interstellar gas. Neutral particles: γ-rays, ν and anti-ν. Some can be identified as coming from ‘point’ sources in the sky like: -ν from Sun and supernovae, -γ rays from sources such as Crab Nebula and active galactic nuclei(AGN). Auger Observatory: charged primary correlated with AGN

5. The spectrum and composition of cosmic rays Direct: Primary particles identified with nuclear emulsion detectors in high altitude balloons. Detectors flown in satellites: -scintillation counters to measure primary nuclear charge. -gas-filled Cerenkov counters to measure particle velocity and energy. Indirect: For GeV-TeV energy region, calorimetric method has been employed: Measuring ionization energy in electromagnetic showers that develop as a result of nuclear cascade which the primary generates as it traverses the thicknesses of absorber.

6. Energy spectrum of cosmic ray protons Above energy of few GeV up to so-called knee at 1014 eV, spectrum follows a simple power law: N(E) dE = const. E-2.7 dE Above knee, spectrum becomes steeper with an index of about -3.0, before apparently flattening off again above 1018 eV at ankle. 1020 eV: 1 baseball(140g) at 60mph Acelerators < 1015 eV

7. The spectrum and composition of cosmic rays Primary spectrum multiplied by E2.7, showing the knee. Isotropy: At energies>30 GeV, where effects of magnetic fields of Earth or Sun are unimportant, radiation appears to be quite isotropic. This is expected at all but the very highest energies: since galactic magnetic fields would destroy any initial anisotropy.

8. Geomagnetic and solar effects Primary radiation, charged particles<10 GeV, show directional and time effects. Charged primaries affected: -by Earth’s magnetic field, like magnetic dipole. -by modulation in time due to solar wind (11y solar cycle). Geomagnetic effects: -Axis of dipole is at an angle to axis of Earth’s rotation. -Geographical coordinates of poles varies slowly with time Calculation of actual orbits of particles incident on Earth as they spiral in dipole field: Particle of charge z|e|, velocity v and momentum p = mv travelling in circular equatorial path of radius r around a short dipole of moment M. Centrifugal and magnetic forces: z|e| |B x v| = mv2/r Equatorial field due to dipole: B= (μ0/4π) M/r3 Radius of orbit(Stormer unit): rS=[(μ0/4π) M z|e|/p]1/2

9. Geomagnetic and solar effects Particle momentum that makes Earth’s radius rE equal to Stormer unit rS: pc/z = (μ0/4π) Mc |e|/(rE)2 = 59.6 GeV Proton of smaller momentum cant reach Earth from eastern horizon at magnetic equator Stormer: equation of motion obeyed by a particle b = rsinθcosλ+cos2λ/r r: distance of particle from dipole centre λ: geomagnetic latitude θ: angle between v and its projection in meridian plane OAB co-moving with particle. b: closest distance of approach to dipole axis by a tangent to particle trajectory.

10. Geomagnetic and solar effects Since |sinθ| < 1, restrictions on values of b, r, λ for allowed trajectories of particles reaching Earth. b = rsinθcosλ+cos2λ/r b  2 is critical in determining which momenta are cut off by the Earth’s field. Solving for r and with b=2 for cut-off momentum at any λ and θ is: r = cos2λ/[1+(1-sinθcos3λ)1/2] Using again the momentum equation: pc/z = (μ0/4π) Mc |e|/(rS)2 (μ0/4π) Mc |e|/(rE)2 = 59.6 GeV pc/z = r2 59.6 GeV since we are concerned with particles arriving at the Earth: r = rE/rS. pc/z = 59.6 GeV {cos2λ/[1+(1-sinθcos3λ)1/2]} 2 For particles incident from vertical: θ = 0 and r = 0.5 cos2λ Cut-off momentum: (pc)min(θ = 0) = 14.9 z cos4λ GeV

11. Geomagnetic and solar effects Vertical(θ = 0) cut-off momentum: pc/z In Europe: λ~ 50 N: 1.1 GeV At magnetic equator: λ~ 0: 14.9 GeV pc/z = 59.6 GeV {cos2λ/[1+(1-sinθcos3λ)1/2]} 2 For λ~0(at magnetic equator): For particles from Eastern horizon (sinθ=+1): 59.6 GeV For particles from Western horizon (sinθ=-1): 10.2 GeV = 59.6/(1 + v2)2 East-west effect: at all latitudes, more (positively charged) particles arrive from West than from East, because of lower momentum cut-off. The effect arises essentially because all positively charged particles are deflected in a clockwise spiral, as viewed from above the N pole.

12. Acceleration of cosmic rays How do cosmic rays obtain their colossal energies, up to 1020eV? Energy density in cosmic rays, coupled with their lifetime in the galaxy, required a power supply similar to the rate of energy generation in supernova shells. Total power requirement to accelerate cosmic rays in the disc: WCR = ρE π R2 D/τ = 2 x 1041 J/y Average energy density ρE of cosmic rays in the galaxy: 1eV/cm3. Our own galaxy: R ~ 15kpc and thickness D ~ 0.2kpc. τ~ 3 x 106 y: average age of a cosmic ray particle in the galaxy, before it diffuses out or is depleted and lost in interactions with interstellar gas. Type II supernova typically ejects a shell of material of about 10 MO(2 x 1031 kg), with velocity ~107m/s into interstellar medium approximately 1/century in our galaxy. Power output per galaxy: WSN = 5 x 1042 J/y. Even galactic supernova rate is uncertain, an efficiency for shockwave to transmit E to cosmic rays of few % is enough to account for total E in cosmic ray beam.

13. Acceleration of cosmic rays At present time, is not at all clear which mechanisms contribute predominantly to the acceleration of cosmic-ray particles. In contrast, extremely energetic cosmic rays are predominantly accelerated in pulsars, binaries, or in jets emitted from black holes or active galactic nuclei. For shock acceleration in supernova explosions: shape of E spectrum of cosmic-rays can be derived from acceleration mechanism.

14. Acceleration of cosmic rays In each cycle of acceleration at shock-front, particle gets energy increment ΔE = αE. After n cycles: In terms of final energy E, # of acceleration cycles: At each stage of the acceleration, particle can escape further cycles. P: probability that particle stays for further acceleration. After n cycles, # of particles remaining for further acceleration: N0: initial number of particles. Substituting for n: s=-lnP/ln(l+α). N: number of particles with n or more cycles, with energy > E. Differential energy spectrum will follow power law dependence:

15. Acceleration of cosmic rays How do we account for the form of the energy spectrum? Differential energy spectrum will follow power law dependence: For shock-wave acceleration: s~ 1.1 Differential spectrum index: -2.1, compared with observed -2.7. Steeper observed spectrum could be accounted for: if escape probability (1-P) was E dependent. Shock-wave acceleration from supernovae shells appears capable accounting for E of cosmic ray nuclei of charge Z|e| up to about 100Z TeV (l014Z eV), but not beyond this. Other, largely unknown, aceleration mechanisms must be invoked for very highest energy cosmic rays.

16. Secondary cosmic radiation Primary particles will produce secondaries Atmosphere: as target in accelerator beam. -Radiation length for γ and e-: 36.66 g/cm2. Αtmosphere corresponds to 27 radiation lengths. -Interaction length for hadrons: 90.0g/cm2. Αtmosphere corresponds to 11 interaction lengths. Compared with total atmospheric depth:1030 gm/cm2 Most commonly produced particles: π+ π- π0. Charged π decay to μ and ν: Neutral π initiate via their decay (π0γ +γ ) electromagnetic cascades, mostly in high atmosphere. absorption length of these cascades is short compared with total atmospheric depth. e- and γ of these cascades are easily absorbed: soft component of cosmic radiation

17. Decay vs. interaction of π (Proper lifetime τ = 26 ns, mc2 = 0.139 GeV. : Decay:Mean free path before decay: λ = γcτ (γ = E/mc2, time dilation factor). For 1 GeV π: λ = 55 m. Interaction: Depends on how much material has the atmosphere. Depth x (gm/cm2): x = X exp(-h/H) X=1030g/cm2 H = 6.5 km In interval Δh(λ=55m): ~0.01H, depth change only by 1%. At GeV almost all charged π decay in flight (rather than interact). ____________________________________________________________________________________________________________________________________________________________________________ Decay: At TeV, π decay probability: ~100 secθ/Eπ[GeV]. θ: zenith angle For E=100GeV, mean free path before decay: λ = γcτ= 5.5 km Interaccion: Depth x (gm/cm2): x = X exp(-h/H) X=1030g/cm2 H = 6.5 km Nuclear absorption: important for charged π with λ ~ H orE>100GeV At TeV majority of π undergo nuclear interaction before they have a chance to decay

18. Secondary cosmic radiation Leptonic decays of π produce penetrating μ and ν μ can also decay and contribute -via their decay e- to soft component -via their decay ν to ν component Εnergy loss of relativistic μ not decaying in atmosphere is low . They constitute with 80% of all charged particles, the largest fraction of secondary particles at sea level. Some secondary mesons and baryons can survive to sea level. Most of low-Ε charged hadrons at sea level are locally produced. Total fraction of hadrons at ground level is very small.

19. Secondary cosmic radiation Daughter μ are also unstable: Decay proper lifetime of τ = 2200 ns. mμ=0.105 GeV. For 1 GeV μ: Mean decay length λ= γcτ (γ = E/mc2) = (1/0.105) c 2200 = 6.6 km, ~ equal to H of atmosphere: x = X exp(-h/H) H = 6.5 km μ of <1 GeV will decay in flight in the atmosphere. No competition with nuclear interaction since μ do not have strong interactions. ______________________________________________________________________________________________________________________________________________________________________________ For 3 GeV μ: Mean decay length λ=20 km, ~ typical distance from point of production to sea-level. Ionization E loss: 2MeV/[gm/cm2] of air traversed(very low). Hard component of cosmic radiation: μ of >3GeV can get through entire atmosphere without decaying or arriving to rest. Higher E μ can reach deep underground. Remaining products of charged π and μ production are ν.

20. Secondary cosmic radiation Intensity of p+, e-, and μ of all E as function of altitude in atmosphere. Αbsorption of p+: ~exponential function. p+ are mostly primaries and interact depending on quantity of material in atmosphere. e- and e+ produced through π0 decay with subsequent pair production reach maximum intensity at altitude of ~15 km soon after are relatively quickly absorbed. While flux of μ is attenuated relatively weakly. μ producedby charged π and Kaons. Mostly μ <3GeV can decay in atmosphere, λ is smaller than available d in atmosphere before reaching the Earth. When μ is in inclined paths, decay probability increase(larger d in atmosphere).

21. Secondary cosmic radiation Because of steepness of E spectra, particle intensities are dominated by low-E particles Low-E particles are mostly of secondary origin. Momentum cut for geomagnetic field for < GeV. If only particles with E>1GeV are counted: -Primary nucleons (p+&neutrons) with initial high E dominate over all particles down to altitudes of 9km, where μ take over(secondary particle). At high altitude: mostly primaries(mostly p+). Only for p+,same graph as for all E with different scale. -μ >1GeV less absorved: hard component -Low interaction probability of ν: ν are practically not at all absorbed in atmosphere. Flux increases monotonically because additional ν are permanently produced by particle decays. E spectrum of primary particles is ~steep, E distribution of secondaries also reflect it.

22. νe and νμ at sea level Besides charged particles, νe& νμ are produced in kaon, π and μ decays: atmospheric neutrinos Βig background for neutrino astronomy. Propagation of atmospheric ν has provided new insights for elementary particle physics, such as ν oscillations. Vertical&horizontal ν spectra: similar as for μ spectra. Parent of ν are dominantly π and kaons, their decay probability is increased compared to interaction probability at inclined directions, horizontal ν spectra are also harder in comparison to the spectra from vertical directions. νμwould appear to dominate

23. νe and νμ at sea level νμwould appear to dominate, since: are strongly suppressed. π and kaons almost exclusively produce νμ. In μ decay: equal numbers of νe and νμ are produced. At high E also semileptonic decays of charmed mesons constitute a source for ν. Based on these ‘classical’ considerations the integral ν spectra yield a ν-flavour ratio of This ratio is modified by propagation effects like ν oscillations.

24. Secondary cosmic radiation Apart from longitudinal development, ΕΜ & hadronic cascades spread out laterally in atmosphere. Lateral size of EM cascade caused by multiple scatteringof e- and e+, in hadronic cascades caused by transverse momentaat production of secondary particles *Comparison of shower development of 100TeV γ and 100TeV protons in atmosphere. Transverse momenta of secondary particles fan out the hadron cascade.

25. Secondary cosmic radiation *Comparison of shower development of 1TeVγ and p+over Chicago ground. Comparison of simulations of p+ and iron shower, simulations of γ and p+.

26. Development of electromagnetic showers Longitudinal development of EM shower: e- of initial E0 traversing a medium. 1. radiation length: e- radiates γ, of energy E0/2. Νext radiation length: γ converts to e--e+ pair, each with E0/4. Οriginal e- radiates a further γ, also of E0/4. Αfter 2 radiation lengths: 1 γ, 2 e-, 1 e+, each of E0/4. In this way, after t radiation lengths: e-, e+, γ in ~equal numbers, each with E(t) = E0/2t. We neglected ionization losses. Cascade multiplication process continues until particle Ε falls to E = EC, critical E, when ionization loss suddenly becomes dominant and no further radiation or pair conversion processes are possible. Cascade reaches a maximum and then ceases abruptly.

27. Development of electromagnetic showers -Shower maximum is at depth t = t(max) = ln(E0/Ec)/ln 2 It increases logarithmically with primary energy E0. -# of particles at shower maximum is N(max) = 2t(max) = E0/Ec Proportional to primary energy. -Number of shower particles> E equal to number created at depths less than t(E): Differential energy spectrum of particles: -Total track-length integral (of charged particles) in radiation lengths: From E conservation: since ionization loss per particle is Ec per radiation length, essentially all incident energy is finally dissipated as ionization E loss. Track-length integral gives a measurement of primary E.

28. Development of electromagnetic showers Effects of both radiation loss & ionization loss are present throughout shower process. Actual shower consists of: -an initial exponential rise, -a broad maximum and -a gradual decline thereafter. Simple model reproduces many of essential quantitative features of actual EM cascades. Model treated shower as one-dimensional. Actual showers spread out laterally, due mostly to Coulomb scattering of e-. Lateral spread of a shower

29. Extensive air showers EAS: Cascades initiated by energetic primary particles which develop in atmosphere. If primary is high energy p+ rather than e-: nuclear cascade develop through atmosphere. Nuclear interaction length in air: ~100 gm/cm2. p+(or heavier nucleus) generates mesons, and they can in turn generate further particles in subsequent collisions. While in EM shower, e- lose bulk of their E in a radiation length, nucleons can penetrate through several interaction lengths, losing only fraction of their E in each encounter, to nucleons as well as mesons. In air, nuclear interaction length is 2.5 times radiation length: cascades initiated by nucleons are much more penetrating than EM cascades.

30. Extensive air showers EAS has ΕΜ, muonic, hadronic, and ν component: Αir shower develops shower core of energetic hadrons(nucleons), which inject permanently Ε into more widely spread ΕΜ component (by fresh π0 production and decay and fresh ΕΜ cascades) and other shower components. π0, which are produced in nuclear interactions, whose decay γ produce e- and e+ via pair production, continually fed e-,e+ and γ component. e-,e+ and γ initiate ΕΜ cascades through alternating processes of: pair production and bremsstrahlung. μ and ν components are formed by decay of charged π and kaons.

31. Extensive air showers Development of EM cascades is shown for various primary E. Particle intensity increases initially in parabolical fashion and decays exponentially after maximum of shower has been reached. Longitudinal profile of particle # parameterized: N(t) ~ tα e-βt t = x/X0: shower depth in units of radiationlength α and β are free fit parameters. Position of shower maximum varies only logarithmically with primary E. Total # of shower particles increases linearly with E. (used for E determination of primary particle). Earth’s atmosphere represents a combined hadronic and EM calorimeter. Critical E in air is Ec = 84 MeV.

32. Extensive air showers(EAS) Atmosphere is ~ a target of 11 interaction lengths & 27 radiation lengths. Minimum E for primary particle to be reasonably measured at sea level via particles produced in air shower is ~1014 eV. Longitudinal development of components of EAS in atmosphere for primary Ε=1015 eV Particle #: N, at sea level in its dependence on primary E: E0 N = 10-10E0[eV] .

33. Neutrinos “Neutrino physics is largely an art of learning a great deal by observing nothing.” Limits of classical astronomy:observations in radio, infrared, optical, UV,X-ray, γ-ray have limit due to EM radiation is quickly absorbed in matter. One can only observe the surfaces of astronomical objects. Energetic particles from distant sources are attenuated via interactions with γ of CMB. Requirement for an optimal astronomy: 1. Optimal astroparticles or radiation should not be influenced by magnetic fields. 2. The particles should not decay from source to Earth. 3. Particles and antiparticles should be different: for distinguish origin from matter or antimatter source. 4. Particles must be penetrating so that one can look into the central part of the sources. 5. Particles should not be absorbed by interstellar or intergalactic dust or IR or CMB γ. These requirements are fulfilled by ν in an ideal way! Why ν astronomy has not been a major branch of astronomy? ν can escape from the center of the sources because its low interaction cross section. But also enormous difficulty to detect ν on Earth.

34. Neutrinos For solar ν ~ several 100 keV, cross section for ν–nucleon scattering: σ(νeN) ~10−45 cm2/nucleon Interaction probability of ν with our planet Earth at central incidence is φ = σ NA d ρ ~ 4 Χ 10−12 NA:Avogadro number, d: diameter of the Earth, ρ: average density of the Earth. From 71010ν/cm2s radiated by Sun & arriving at Earth only 1 at most is seen here. ν telescopes must have an enormous target mass, and long exposure times. For high E, interaction cross section rises with ν E. ν ~several 100 keV can be detected by radiochemical methods. For Ε> 5 MeV large-volume water Cherenkov counters are an attractive possibility. Neutrino astronomy is a very young branch of astroparticle physics.

35. High energy Neutrinos Is considered realistic that point source in our galaxy produces ν spectrum according to: This leads to an integral flux of ν: The interaction cross section of high-energy ν was measured at accelerators: σ(νμN) = 6.7 10−39Eν [GeV] cm2/nucleon. For 100 TeV ν: σ~ 6.7 Χ 10-34 cm2/nucleon. For target thickness of 1km, an interaction probability W per ν: W = NA σ d = 4 Χ 10 −5 For d = 1 km, ρ(ice) ~1 g/cm3. Total interaction rate R obtained from integral ν flux Φν , interaction probability W, effective collection area Aeff = 1 km2, and a measurement time t . Event rate: R = Φν W Aeff = ~250 events/year.

36. High energy Neutrinos Assuming ~half a dozen sources in our galaxy, estimate would be ~4 events/day. Besides point sources, events from diffuse ν background carries little astrophysical information. Excellent candidates within our galaxy: supernova remnants of Crab Nebula and Vela, galactic center, and Cygnus X3. Extragalactic candidates could be Markarian galaxies Mrk421, Mrk 501, M87, quasars. ν astronomy was pioneered with Baikal telescope installed in lake Baikal in Siberia. The most advanced larger telescopes are AMANDA/ICECUBE in the South pole and NESTOR/ANTARES/ΝΕΜΟ detector in the Mediterranean coasts of Greece, France and Italy. Real ν astronomy will require larger detectors. Auger experiment could also detect high energy ν events.

37. Gamma Astronomy An important, so far unsolved problem of astroparticle physics: origin of cosmic rays. Investigations of charged primary cosmic rays are essentially unable to answer this because charged particles have to pass through extended irregular magnetic fields on their way from source to Earth. This causes them to be deflected in an uncontrolled fashion, forgetting their origin. Particle astronomy with charged particles is only possible at extremely high E when are no significantly affected by cosmic magnetic fields. Would require E >1019 eV with flux of primary particles extremely low. Whatever the sources of cosmic rays are, they will also emit energetic penetrating γ rays not deflected by intergalactic or stellar magnetic fields and so point back to sources. However γ rays from distant sources might be subject to time dispersions. Astronomical objects in the line of sight of these sources can distort their trajectory by gravitational lensing making them look blurred and causing time-of-flight dispersions in arrival time also for electromagnetic radiation.

38. Extensive air showers Even EAS initiated by primary particles with E<100TeV doesn’t reach sea level, it can be recorded via Cherenkov light emitted by shower particles. As relativistic particles traverse the atmosphere, part of E loss appears as a coherent wavefront of Cerenkov radiation. This radiation is mostly in ultraviolet or blue region of the spectrum. Huyghens construction for emission of Cerenkov light by a relativistic particle: Cos θ = (ct/n)/(βct)=1/(βn) β> 1/n Refractive index n of air at ground: ε=n-1= 0.0003. Threshold E for e-: mc2/(1-β2)1/2 =mc2/(2ε)1/2=21MeV. For μ: 4.3GeV (mμ= 106 MeV). Most components of EAS have much greater E, so they will produce abundant Cerenkov light. Relativistic particle above threshold: 10000γ/km of path. Can be detected by large mirrors pointing to photomultipliers:Whipple Observatory

39. Extensive air showers Cerenkov light emitted in narrow cone of θ~(2ε)1/2(=1.4° at ground, although Coulomb scattering of e- will considerably broaden this), so that light appears in restricted radius ~100m around shower axis, axis must be fairly close to mirror system to be recorded. Ionizing particles can excite fluorescence from N2 in the atmosphere: 5000γ/km of track in the blue wavelength region. Fluorescent light is emitted isotropically:distant showers several km away, not aimed towards mirror/photomultiplier system, can be detected. Sensitivity to highest E events greatly increased. Whipple Observatory: 1.system employing these techniques with large mirror array. 2 spatially separated arrays of mirrors for stereo images to reconstruct shower profile. Distinguish showers initiated by primary γ: develop early, contained in upper atmosphere, from those by nucleons:develop slowly,penetrating. Poor duty cycle: cloudless, moonless nights.

40. γ-rays Air Cerenkov telescopes: interesting type of γ-ray detector. Τypical detector must be flown with balloon or satellite above atmosphere to avoid absorption of γ-ray, Air Cerenkov telescope nullifies problem by making atmosphere part of detector! γ-rays interacting in atmosphere create an air shower. Depending on Ε of initial cosmic γ-ray, may be thousands of electrons/positrons in cascade emitting Cerenkov radiation. Light is pancake-like: ~200m in diameter but ~ 1m thickness. HESS,MAGIC,... VERITAS (Very Energetic Radiation Imaging Telescope Array System), built by a collaboration headed by the Whipple Observatory, uses an array of seven 10m optical reflectors for gamma-ray astronomy in 50 GeV - 50 TeV. Solar Tower Atmospheric Cerenkov Effect Experiment (STACEE) will use primary collection mirror: large field of 220 solar heliostat mirrors at National Solar Thermal Test Facility of Sandia National Laboratories. Milagro built by collaboration headed by Los Alamos National Laboratory, use 5000m2 pool of water covered with light-tight barrier as Cerenkov detector to study TeV γ-rays.

41. γ-rays Observing the Universe in γ-rays allows us to examine things which are happening that cannot be seen with ordinary telescopes and which are very important in helping us to understand how matter and radiation interact with each other. This is especially true for understanding their interaction under extreme conditions: where temperatures are hundreds of millions degrees, matter is very dense, or magnetic fields are very strong. Some specific targets include: solar flares Gamma-ray Bursts Black Holes and Neutron Stars Supernovae Pulsars Active Galaxies: Seyferts and Quasars

42. Extensive air showers At higher E: various detection techniques. Classical technique:sampling of shower particles at sea level with ~1m2scintillators or water Cherenkov counters.Auger 75y ago: extended array of detectors in coincidence. Shower detectable at sea-level for primary E>1015eV, when maximum is near ground. At mountain altitudes, threshold ~100 TeV. E assignment for primary not very precise. Shower develops in atmosphere which acts as calorimeter of 27 radiation lengths thickness. Information on shower is sampled in only one, the last layer of calorimeter and coverage of this layer is typically only ~1%. Direction of incidence of primary obtained from arrival times of shower particles in different sampling counters as shower front crosses array. Since shower front is quite well defined.

43. Extensive air showers More advantageous to measure total longitudinal development of cascade in atmosphere Apart from directional Cherenkov radiation shower particles emit isotropic scintillation light in atmosphere. For particles with E>1017 eV, fluorescence light of N is sufficiently intense to be recorded at sea level in presence of diffuse background of starlight. Detector consists of a system of mirrors and photomultipliers, which view the sky. Air shower passing through atmosphere near activates only those photomultipliers whose field of view is hit. Fired photomultipliers allow to reconstruct longitudinal profile of air shower.

44. Extensive air showers Total recorded light intensity to determine shower E: more precise E assignments. Big disadvantage compared to classical air-shower technique: only clear moonless night Arrangement of mirrors and photomultipliers in Fly’s Eye setup of Utah. Auger experiment: array of sampling detectors complemented by telescopes measuring fluoresce light produced in atmosphere. Much larger acceptances of these telescopes in orbit: ‘Air Watch’.

45. Extensive air showers -Ηas been tried to observe air showers via EM radiation emitted in radio band. Is believed: this radio signal is caused by shower e- deflected in Earth’s magnetic field creating synchrotron radiation. Because of strong background in all wavelength ranges, these attempts have not been particularly successful so far. -Possibility to detect large air showers via their μ content in underground experiments has been followed up in recent experiments.

46. Ultrahigh Energy cosmic rays -AGASA -Fly’s Eye -HiRes -Telescope Array Auger Observatory: Biggest ultra high energy cosmic ray detector on Earth: http://www.auger.org/ http://www.auger.org.ar/