UHECR: Acceleration and Propagation

Transcription

1 UHECR: Acceleration and Propagation V. Berezinsky INFN, Gran Sasso Science Institute and Laboratori Nazionali del Gran Sasso, Italy

2 ACCELERATION UHE particles with energies observed up to E 3 20 ev can be in principle accelerated e.g. by shocks, unipolar induction and strong electromagnetic waves. Large E max combined with large luminosity is a very limiting factor for shock acceleration above 19 ev. However, AGN remain most promising candidates.

3 E max for non-relativistic jets in AGN Biermann and Strittmatter 1987, Norman, Melrose, Achtenberg 1995, Ptuskin, Rogovaya, Zirakashvili, 2013 E max from two conditions: E max = ZeBβ s R s (Hillas criterion) and B 2 /8π = ω part or B 2 /8π L/πRscβ 2 (equipartition), results in E max Zeβ s (8L/c) 1/ Zβ s L 1/2 45 ev (1) Eq. (1) does not depend on r sh and R s. Problem: At Γ j < 4 jets are short, and HE protons are absorbed due to pγ interaction.

4 Fanaroff-Riley I and II radio-galaxies

5 ACCELERATION IN RELATIVISTIC SHOCKS Detective story in five acts

6 act 1 GREAT EXCITEMENT In a single reflection particle obtains E Γ 2 sh E i

7 act 2 Efficiency in further crossings is low E Γ 2 shξ n E i with ξ 1.7

8 act 3 full disaster!! Capturing of particles downstream Perpendicular large-scale magnetic field B d. B d = Γ sb u, E is induced. Drag of particles downstream by flow of gas (quasi-helical orbits). Particles cannot return to upstream region.

9 act 4 Γ 2 -Acceleration Renaissance 2011 Sironi and Spitkovsky (2011) found in low-magnetised plasma σ = B 2 4πnm p c 2 1, streaming (Weibel) instability which results in production of smallscale turbulence with size λ c/ω pp. Scattering of particles on these micro-turbulences results in repeating transition between downstream and upstream regions and thus in Fermi regime of acceleration. (Lemoine and Pelletier , Bykov et al 2012, Reville and Bell 2014).

10 act 5 Epilogue 2015 Reville and Bell 2014 included in calculations the new element, the growth time of instability. There are two competing processes: isotropisation of particles due to scattering and drift of particles downstream, with characteristic times Dθ 1 and R L /c, respectively. Acceleration occurs when Dθ 1 < R L /c, and Emax of acceleration is determined by equality of these quantities. E max ( Γsh ) 2 ( ) ( ) ( λd σd σu 0 c/ω pp 2 8 ) 1/2 PeV, The allowed Emax is too small.

11 B. Reville and A.R. Bell 2014 The calculated growth-rates (of plasma instability) have insufficient time to modify the scattering, the acceleration to higher energies is ruled out. Ultra-relativistic shocks are disfavoured as sources of high energy particles, in general... this paper is not the first to suggest that GRBs are not the sources of UHECRs, but we gone one step further..

12 UHECR: propagation, signatures and mass composition

13 Spectrum and Spectral Features s pp (GeV) 5 6 ) 1.5 sec -1 sr -1 ev ATIC PROTON RUNJOB KASCADE (QGSJET 01) KASCADE (SIBYLL 2.1) KASCADE-Grande (prel.) Tibet ASg (SIBYLL 2.1) HiRes-MIA HiRes I HiRes II Auger SD J(E) (m E p-knee Fe-knee ankle GZK E (ev)

14 0 * * - * ) " # Where is the transition? KASCADE-Grande found the light component with the following properties: p+he component at EeV separated as electron-rich extragalactic, otherwise anisotropy at E 1 EeV. flat spectrum γ = 2.79 ± 0.08, cf γ = 3.24 ± 0.08 for total. ' 1. %.,/. + $,+ $&% ' ( "! C 7 j Hidden ankle transition VWYXZYW\[Y]J^ _` abccd HJI KLM&N OLO&N HSI KLTU OLOK HJI PLK&N OLO&N 7 h fecg 7 i fecg HJI PLK&Q OLOR HSI PLK&Q OLO&N HSI KLTM OLOR CB CBD E CG CGCD E F 8:9<;,=?>A@

15 Signatures of particle propagation through CMB and EBL CMB + EBL -5-6 Iron A=56, z=0 τ -1 A -1 de/dt(e), yr -1 E -9 - total adiabatic y β A pair EBL e e pion production - H E, ev Γ E eq1 = ev, E eq2 = ev Nuclei photo-dissociation: GR cutoff Pair-production dip and GZK cutoff. τ ebl A (Γ c) = τ cmb A (Γ c). Γc = 3.2 9, Ec = ev

16 UHE protons INTERACTION SIGNATURES AND MODEL- DEPENDENT SIGNATURES We want to see observational signatures of interaction, but in our calculations model-dependent quantities also appear, such as distances between sources, their cosmological evolution, modes of propagation (from rectilinear to diffusion), local source overdensity or deficit etc. Energy spectrum in terms of modification factor characterizes well the interaction signatures.

17 MODIFICATION FACTOR η(e) = J p(e) (E) J unm p where Jp unm (E) = KE γ g includes only adiabatic energy losses. Since many physical phenomena in numerator and denominator compensate or cancel each other, dip in terms of modification factor is less model-dependent than J p (E). It depends very weakly on: γ g and E max, modes of propagation (rect or diff), large-scale source inhomogeneity, source separation within 1-50 Mpc, local source overdensity or deficit,.. It is modified by presence of nuclei (> 15%). Experimental modification factor: η exp (E) = J obs (E)/KE γ g. η(e) γ g = E, ev 21 - e + e total 22

18 Comparison of pair-production dip with observations 0 0 modification factor -1 Akeno-AGASA η ee modification factor -1 Yakutsk η ee -2 γ g =2.7 η total -2 γ g =2.7 η total E, ev E, ev modification factor HiRes I - HiRes II γ g =2.7 η ee η total modification factor TA MD TA SD γ =2.6 g η ee η total E, ev E, ev 20 21

19 GZK CUTOFF IN HiRes DIFFERENTIAL SPECTRUM 0 modification factor -1 HiRes I - HiRes II η ee -2 γ g =2.7 η total E, ev

20 GZK CUTOFF IN HiRes INTEGRAL SPECTRUM J(>E)/KE γ log (E) (ev) E 1/2 in HiRes integral spectrum confirms that steepening in the differential spectrum is the GZK cutoff: E meas 1/2 = 19.73±0.07 ev cf E theor 1/2 = ev

21 DIRECT MEASUREMENTS OF MASS COMPOSITION is a necessary component of consistent picture

22 MASS COMPOSITION: HIRES (top) vs AUGER (bottom)

23 Interpretation of Auger spectrum and mass composition Aloisio, V.B., Blasi (2013), see also Taylor, Ahlers, Aharonian (2012). γg = 1.0, Emax = 5Z EeV γg (p, He) = 2.7 E 3 J(E) (ev 2 m -2 s -1 sr -1 ) γ g =1.0, E max =5Zx 18 ev p He CNO MgAlSi Fe E 3 J(E) (ev 2 m -2 s -1 sr -1 ) γ g (A>4)=1.0, γ g (p,he)=2.7 E max =3Zx 19 ev p He CNO MgAlSi Fe E (ev) E (ev) <X max > (g/cm 2 ) EPOS Sibyll QGSJet1 QGSJet2 σ(x max ) (g/cm 2 ) E (ev) E (ev)

24 0 * * - * ) " # Impact of KASCADE-Grande experiment KASCADE-Grande found the light component with the following properties: p+he component at EeV separated as electron-rich extragalactic, otherwise anisotropy at E 1 EeV. flat spectrum γ = 2.79 ± 0.08, cf γ = 3.24 ± 0.08 for total. ' 1. %.,/. + $,+ $&% ' ( "! C 7 j VWYXZYW\[Y]J^ _` abccd HJI KLM&N OLO&N HSI KLTU OLOK HJI PLK&N OLO&N 7 h fecg 7 i fecg HJI PLK&Q OLOR HSI PLK&Q OLO&N HSI KLTM OLOR CB CBD E CG CGCD E F 8:9<;,=?>A@

25 AUGER MASS COMPOSITION, September 2014 Phys. Rev. D 90 (2014)

26 Auger Xmax and RMS : 2014 vs 2011 Xmax [g/cm 2 ] data± stat ± sys proton iron EPOS-LHC Sibyll2.1 QGSJetII-04 (Xmax) [g/cm 2 ] proton iron E[eV] E[eV]

27 Iron and Proton fractions pfraction Hefraction N fraction Fefraction Sibyll 2.1 QGSJET II-4 EPOS-LHC

28 Auger 2014: summary p+he is dominant composition up to EeV with fraction of intermediate nuclei increasing up to highest energies. Proton fraction is observed at all energies. It is dominant (60-80)% up to 2 EeV, falling down at 4 EeV, with minimum at (-20) EeV and with resurgence at higher energies. The presence of proton component at all energies excludes rigiditydependent E max with Ep max around (4-5) EeV, widely used in most models. Since protons below 40 EeV are extragalactic, ankle as transition from galactic to extragalactic CRs is excluded. Iron fraction is very small at all energies

29 CONCLUSIONS The propagation signatures for protons are pair-production dip (p+γ cmb p+e + +e ) and GZK cutoff (p+γ cmb N +π). The propagation signature for nuclei is GR cutoff with Γ c (3 4) 9 for all nuclei, and E GR AΓ c m N (3 4)A 18 ev. HiRes and TA observed the the proton signatures further confirmed by proton-dominated mass composition. Auger (2013) reports the nuclei composition steadily heavier with increasing energy. The models which explain simultaneously the Auger energy spectrum, X max (E) and RMS (dispersion) must have very flat generation spectrum γ g < 1.6 and additional EeV proton+he component with steep spectrum.

30 THANK YOU!!

31 PAIR-PRODUCTION DIP in Auger data Energy scale of each detector has to be shifted by factor λ to minimize χ 2. For HiRes and TA λ 1. To reach χ 2 min for PAO λ = 1.22 is needed. Equality of fluxes after recalibration is confirmation of pair-production nature of the dip. E 3 J(E), ev 2 m -2 s -1 sr HR 1 HR 2 TA MD TA SD PAO 22 γ = 2.5, E = ev, z =4, m=3 g max max E 3 J(E), ev 2 m -2 s -1 sr HR 1 HR 2 TA MD TA SD PAO with 22% energy upscale 22 γ = 2.5, E = ev, z =4, m=3 g max max 19 E, ev E, ev 20

32 0 * * - * ) " # STATUS of ANKLE Two competitive scenarios: ankle as transition and ankle as intrinsic feature of the dip. Auger, HiRes, TA: E a = (4 5) EeV and at E < E a : light nuclei Ankle as transition ' 1. %.,/. + $,+ $&% ' ( "! Where is the transition? VWYXZYW\[Y]J^ _` abccd 7 h fecg HJI KLM&N OLO&N HSI KLTU OLOK C 7 j HJI PLK&N OLO&N 7 i fecg HJI PLK&Q OLOR HSI PLK&Q OLO&N HSI KLTM OLOR CB CBD E CG CGCD E F 8:9<;,=?>A@

33 0 * * - * ) " # Impact of KASCADE-Grande experiment KASCADE-Grande found the light component with the following properties: p+he component at EeV separated as electron-rich extragalactic, otherwise anisotropy at E 1 EeV. flat spectrum γ = 2.79 ± 0.08, cf γ = 3.24 ± 0.08 for total. ' 1. %.,/. + $,+ $&% ' ( "! C 7 j VWYXZYW\[Y]J^ _` abccd HJI KLM&N OLO&N HSI KLTU OLOK HJI PLK&N OLO&N 7 h fecg 7 i fecg HJI PLK&Q OLOR HSI PLK&Q OLO&N HSI KLTM OLOR CB CBD E CG CGCD E F 8:9<;,=?>A@