Lessons 19 and 20. Detection of C.R. with energy > TeV Study of the C.R. isotropy/anisotropy Ground based detectors:

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1 Lessons 19 and 20 Detection of C.R. with energy > TeV Study of the C.R. isotropy/anisotropy Ground based detectors: Detection at ground of extensive Air Showers: nature, direction and energy of the primary C.R. Measurement of H.E. photons and C.R.s with detectors at high quote over sea level (the ARGO and MILAGRO experiments) A.A Prof. Antonio Capone - Particle and AstroParcle Physics 1

2 Cosmic Rays isotropy/anisotropy The density matter is supposed to be uniform into a narrow band, in "declination" (-90 o,+90 o ) that spans on the full range in "right ascension" (-180 o,+180 o ). If the C.R. sources are uniformly distributed in the sky the arrival directions of C.R. should be isotropic. In this case we can define the average of C.R. for an interval "i" in declination as! " #$%&#'% = *+, /,* A.A Prof. Antonio Capone - Particle and AstroParcle Physics 2 8 and in each "i,j" bin (declination, right ascension) we expect to find %:;%<=%> #$%&#'% #$%&#'%! ",9 =!" ±!"

3 Representing the arrival C.R. directions, the sky Horizontal coordinates system. Equatorial coordinates system. The coordinates of the fixed equatorial system are: - the time angle (H) (right ascension), which is the angular distance between the mid-point and the intersection of the celestial meridian passing through the star with the celestial equator; it is measured in hours, minutes and seconds (0h, 24h) starting from point clockwise (or in degrees 0 o, 360 o ); - the declination, i.e. the angular distance between the intersection of the celestial meridian for the star and the celestial equator and the star itself, measured along the celestial meridian; it is measured in degrees, first and second (0 o, 90 o ) starting from the equator celestial to the celestial poles; we speak of positive declination in the northern hemisphere and negative declination in the austral one. A.A Prof. Antonio Capone - Particle and AstroParcle Physics 3

4 What's the point? The gamma point (from the symbol similar to γ that distinguishes the constellation of Aries), is one of the two equinoctial points in which the celestial equator intersects the ecliptic. When the Sun, in its apparent annual motion, passes through this point, the Earth finds itself in correspondence with the spring equinox: it is the point at which the Sun is positioned on March 21 st calculated from the position of the Earth. In the last 2100 years, the precession of the equinoxes has rotated the Earth's axis by 30 to its right: at the spring equinox, while 2100 years ago the Sun was passing through the constellation of Aries, today, due to the precession, the same transits in that of Pisces. A.A Prof. Antonio Capone - Particle and AstroParcle Physics 4

5 so, the sky coordinates In Equatorial coordinates: - the declination (δ) of a star is its angular distance from the celestial equator (from -90 o to the south pole, +90 o to the north pole) - the right ascension (α) of a star is the angular distance between the point and the intersection of his hour circle with the celestial equator; it is measured starting from the point of rotation counter-clockwise in degrees (0 o, 360 o ) or equivalently in hours placing 1h = 15 o. A.A Prof. Antonio Capone - Particle and AstroParcle Physics 5

6 CR anisotropies? The Compton-Getting effect The CR flux on Earth is consistent with isotropy when the low-energy particles affected by the Sun are neglected. Small anisotropies are expected due to the global leakage of CRs from the Galaxy, to the possible contribution of individual sources, and due to the motion of the solar system in the Galaxy. In general, the presence of a cosmic ray anisotropy is strictly correlated with the streaming velocity V of the CR particles. This streaming velocity plays the same role as the drift velocity attained by electrons in the presence of an electric field. There is an anisotropy only if there is a net streaming velocity, which can expressed with a particular amplitude and phase. The amplitude of the CR anisotropy is defined as: δ I max I min I max + I min Imax, Imin represent the maximum and minimum intensity of cosmic rays from a given direction. A.A Prof. Antonio Capone - Particle and AstroParcle Physics 6

7 One example of "Large Scale Anisotropy" If the flux of Cosmic Rays is isotropic then the number of C.R. in each longitude bin should be compatible with a uniform distribution. If there is ONE source of C.R., or a reason for an excess of C.R., in one bin in "right ascension" the intensity of C.R. from the source direction will increase with respect to the average evaluated along the full declination band (and a deficit of C.R. will appear at 180 o angular distance): the distribution of C.R. will show a "dipole". Several experiment have indicated that the C.R. arrival distribution is not isotropic and can be well represented with a "dipole". For example PAMELA reported the result shown in the figure on the side: Is is the expected intensity of C.R. in each bin in the hypothesis of isotropy, Ir is the measured intensity. In this analysis Is and Ir are intensities integrated over the full range in declination. In general anisotropies are energy and coordinates dependent. Journal of Physics: Conference Series 675 (2016) doi: / /675/3/032005! " = $ % cos " * PAMELA A= , φ =70 10 degrees In this analysis the "reference flux" Is has been obtained "scrambling" the observed data (attributing to the events a "wrong time"). The same events has been used ~100 times, with different "sidereal time" in order to reduce the fluctuations on Is. A.A Prof. Antonio Capone - Particle and AstroParcle Physics 7

8 CR flux anisotropy vs detector position and energy A.A Prof. Antonio Capone - Particle and AstroParcle Physics 8

9 A data compilation on CR anisotropy Usually, data are projected along the R.A. projection (e.g. IC22): Then a A 2-harmonics fit is performed and amplitude and phase of the first harmonics are discussed (see the compilation for reference). They are generally interpreted as important signature, as the dipole is a trace of the source distribution. BUT From ARGO-YBJ 32 ICRC contribution A.A Prof. Antonio Capone - Particle and AstroParcle Physics 9

10 Other examples of measured C.R. anisotropy A.A Prof. Antonio Capone - Particle and AstroParcle Physics 10

11 Representation of anisotropies with spherical harmonics Given a spherical coordinate system, a point on a sphere of unit radius is identified by the versor where we indicated with θ and φ, respectively, the angle of zenith and azimuth. Spatial distribution on this unit sphere of a series of objects can be described through the use of a series of functions, called spherical harmonics, that depend on the two angles θ and φ. Spherical harmonics are an orthogonal set of functions solution of the Legendre equation. The solutions of the Legendre equation are polynomial (having fixed l positive and integer) and are a generalization of the Legendre polynomials which are obtainable for m = 0. These solutions have the expression: where Pl (x) are the Legendre polynomials. The spherical harmonics are therefore defined as: with " l. A.A Prof. Antonio Capone - Particle and AstroParcle Physics 11

12 Representation of anisotropies with spherical harmonics Spherical harmonics are a set of orthonormal functions, satisfying the following orthogonality rule: explicit form of the spherical harmonics up to the third degree (l = 3) A.A Prof. Antonio Capone - Particle and AstroParcle Physics 12

13 Representation of anisotropies with spherical harmonics Any distribution Φ(θ,φ) on the unit sphere can therefore be described through the development in multipoles, that is through a combination of spherical harmonics! l #, each multiplied by the respective coefficient $ l #, through the expression: where n is the maximum degree of approximation and Φ & ' is a constant. For n=0 we obtain the isotropic component of the distribution Φ(θ,φ): For n=1 the relative dipolar component of the distribution Φ(θ,φ) is also obtained where: is the versor of the generic direction (θ,φ) while ((* +,-, / +,- ) is the dipole vector, relative to the direction (θ dip, φ dip ) A.A Prof. Antonio Capone - Particle and AstroParcle Physics 13

14 Representation of anisotropies with spherical harmonics!(# $%&, ( $%& ) is the dipole vector, relative to the direction (θ dip, φ dip ), defined as For n=2 the sum is extended to the second order, which returns the term of quadrupole. By increasing the value of n, the terms of the expansion of ever higher order are then introduced, obtaining an always better approximation of the distribution that one wants to describe. A.A Prof. Antonio Capone - Particle and AstroParcle Physics 14

15 Another example on real data (ANTARES) The figure shows the "deviations" from the mean value of the number of "down-going" muons measured by ANTARES, as a function of the right ascension angle (incorrect data for all possible systematic effects). We try to represent such data with a "constant", with a harmonic function of the first order and with a function in which the first and second order appear A.A Prof. Antonio Capone - Particle and AstroParcle Physics 15

16 ARGO: Large scale Anisotropy (LSA) A.A Prof. Antonio Capone - Particle and AstroParcle Physics 16

17 ARGO: Medium Scale Anisotropy (MSA) A.A Prof. Antonio Capone - Particle and AstroParcle Physics 18

18 C.R. observed anisotropy Abbasi R. et al. (IceCube Collaboration), ApJ 746, 33 (2012) A.A Prof. Antonio Capone - Particle and AstroParcle Physics 21

19 Recent observations of CR anisotropy 10 TeV 5 TeV MILAGRO ApJ Super-Kamiokande ICRC 2007 Proceedings 2 TeV ARGO-YBJ ICRC 2011 Proceedings 20 TeV 4 TeV Tibet AS-γ - Science 20 October 2006: Vol. 314 no pp ICE-CUBE ApJ 718 L194 A.A Prof. Antonio Capone - Particle and AstroParcle Physics 22

20 IceCube: study of TeV-PeV Cosmic-Ray anisotropy A.A Prof. Antonio Capone - Particle and AstroParcle Physics 23

21 LSA as a function of the primary energy Anisotropy as a function of CR Energy 0.9 TeV ARGO-YBJ Tibet ASγ 1.5 TeV 2.4 TeV 3.6 TeV 7.2 TeV 12.5 TeV 23.6 TeV Anisotropy seems to disappear. From the absence of the CG effect they infer the corotation of GCR with the GMF environment A.A Prof. Antonio Capone - Particle and AstroParcle Physics 24

22 The observed CR anisotropy power spectrum (the old 2 harmonics ) ICECUBE has been the first experiment showing a CL spectrum of the arrival direction distribution. Strong L=2-3-4 components are visible. There are strong L=2-3-4 components in the CR anisotropy, even below ev. If dipole means sources, what is this power related to? When a traditional 1D R.A. projection is presented, a 2 harmonics function is fot to the experimental distribution (ARGO-YBJ example). A.A Prof. Antonio Capone - Particle and AstroParcle Physics 25

23 What can we learn from the observed anisotropies? Stochastic MHD approach Energy-dependent small scale anisotropies naturally arise from the local concrete realization of the turbulent magnetic field within the cosmic ray scattering length. Giacinti& Sigl Phys. Rev. Lett. 109, (2012) a The CR arrival distribution at Earth contains multipoles: Dipole amplitude Dipole direction Direction after the propagation of the particle with initial direction n. It depends on the magnetic field turbulence spectrum! There is a connection between the observed angular power spectrum and the magnetic field turbulence spectrum. A.A Prof. Antonio Capone - Particle and AstroParcle Physics 26

24 19 Outlook to the future: towards a Outlook to the future: towards a complete CR sky-map complete TeV CR TeV sky-map ARGO-YBJ + IceCube-59 3 hr = 45 PSF-Smoothed map ARGO-YBJ 1 TeV Smoothing radius 10 A.A Prof. Antonio Capone - Particle and AstroParcle Physics 27

25 C.R. isotropy/anisotropy M. Spurio Particle and Astrophysics - Springer Fig. 5.5 The anisotropy amplitude as a function of energy. In red are the limits obtained by the Auger Observatory over the full energy range as reported at the ICRC in 2013 [see Abreu et al. (2011) forthereferencetotheexperiments].thelinesdenotedasaandsupto10 18 ev refer to predictions for two different galactic magnetic field models. The predictions for a purely galactic origin of ultra-high energy cosmic rays (UHECRs) is denoted as (Gal), and the expectations from the Compton-Getting effect for an extragalactic component of CRs (C-GXgal). In this case, the CRs are assumed to be isotropic in the cosmic microwave background rest frame. Courtesy of the Pierre Auger Observatory A.A Prof. Antonio Capone - Particle and AstroParcle Physics 28

26 Milagro a water Cherenkov detector to study EAS induced by high energy photons 100 GeV< Eg < 100 TeV A.A Prof. Antonio Capone - Particle and AstroParcle Physics 29

27 Milagro - 1 A.A Prof. Antonio Capone - Particle and AstroParcle Physics 30

28 Milagro - 2 ~ 1000 PMT A.A Prof. Antonio Capone - Particle and AstroParcle Physics 31

29 Milagro - 3 A.A Prof. Antonio Capone - Particle and AstroParcle Physics 32

30 Milagro - 4 Milagro was a water-cherenkov detector at an altitude of 2650m capable of continuously monitoring the overhead sky. It was composed of a central 60m x 80m pond with a sparse 200m x 200m array of 175 outrigger tanks surrounding it. The pond is instrumented with two layers of photomultiplier tubes. The top air-shower layer consists of 450 PMTs under 1.4m of purified water while the bottom muon layer has 273 PMTs located 5m below the surface. The air-shower layer allows the accurate measurement of shower particle arrival times used for direction reconstruction and triggering. The greater depth of the muon layer is used to detect penetrating muons and hadrons. Simple cuts have been developed to distinguish between gamma-ray and hadron/muon induced showers. The outrigger array improves the core location and angular resolution of the detector by providing a longer lever arm with which to reconstruct events. The angular resolution improves from 0.75 to 0.45 when outriggers are used in the reconstruction. Milagro's large field of view (~2!sr) and high duty cycle (>90%) allow it to monitor the entire overhead sky continuously, making it well-suited to searching for new TeV sources and scanning known sources at higher energies. A.A Prof. Antonio Capone - Particle and AstroParcle Physics 33

31 Angular resolution and discovery power Let's define S(>E) and B(>E) the number of Signal and Background events (with energy >E) obtained as the result of data measurement, selection and analysis. We can qualify our discovery capability in terms of the ratio!(> $) &(> $) = ()*+,-./ 012(34,5,(60 > $ ()*+,-./ 012(34,5,(60 > $ The background, usually due to C.R. is isotropic and has flux 7 8(9:) = ; 8 $ <= > The signal is coming from a point source and has flux 7?(9:) = ;? $ Then if I collect data with a detector with effective area A BCC for the time T integrating in a solid angle around the source direction with aperture DE defined by the detector "point spread function", by definition! > $ = ;? $ F G F A BCC while B > $ = ; 8 $ <= > F G F DE H I F A BCC and?(9:) MFN OPP 8(9:) = J.06 $(K> L QR The discovery potential grows slowly with T and A BCC and improves very fast improving the angular resolution (reducing DE ) source direction Angular smearing due to resolution PSI=point spread function DE detector A.A Prof. Antonio Capone - Particle and AstroParcle Physics 34

32 Milagro Cosmic Ray Observations A.A Prof. Antonio Capone - Particle and AstroParcle Physics 35

33 MILAGRO survey of the Galactic Plane MGRO J Boomerang PWN MGRO J MGRO J Geminga Crab A.A Prof. Antonio Capone - Particle and AstroParcle Physics 36

34 Fermi LAT Brigh Fermi and MILAGRO the MeV TeV connection for Gamma Rays Sources Milagro s strongest sources are very likely TeV PWN. Typical TeV source is a PWN. TeV emission is quite commonly associated with MeV GeV Pulsars. Spectrum to connect Milagro measurements to Fermi measurements are universally softer than 2.3. A.A Prof. Antonio Capone - Particle and AstroParcle Physics 37

35 MILAGRO searches for point like sources An example: Markarian 421 A.A Prof. Antonio Capone - Particle and AstroParcle Physics 38

36 Charged primary Cosmic Rays for E > TeV So far we have mainly discussed experiments measuring gamma fluxes: very good tool for astronomy large background due to the much more intense charged component High energy charged primary cosmic rays carry many information: what happens for E~10 15 ev does the primary CR composition changes with energy?? Can our detector distinguish a light CR (proton, He, ) from an heavy one (Fe, )? are these CR of galactic origin or there is an extragalactic component? What kind of experimental technique can answer to all these questions? A.A Prof. Antonio Capone - Particle and AstroParcle Physics 39