Michael Hillas University of Leeds

1. Old and new ways of looking at UHECRs.  A happy accident? Michael Hillas University of Leeds A tribute to Veniamin Berezinsky ------ 1. Lightning historical tour: the GZK hunt 2. Berezinsky argues for UHE spectrum of protons, with 2 GZK falls 3*. The challenge and excitement of Auger 2007: a new kind of anisotropy 4. Older experiments are still relevant 5. A challenging problem – and enormous promise SOCoR Trondheim 16 June 2009

2. 1 | THE GZK HUNT 2 | 3 | 4| 5 (1) 1966 STARTED THE HUNT FOR THE GZK “cutoff” 1965 1966 1967 knee knee ? EscapingGalactic CR Cosmic-ray Flux / E-n There should be an end (G, Z & K) “extragalactic” ? ? o o 1015 1020 ankle 1015 1020 View of the cosmic ray spectrum Greisen & Zatsepin & Kuzmin --- spectrum could not go so far (Linsley & Scarsi had reported 1020 eV) unless sources were very close ?marks items that I would doubt today

3. 1 | THE GZK HUNT 2 | 3 | 4| 5 and 2007-8: The Hi-Res Spectrum of UHE Cosmic Rays The earlier result from AGASA (no fall) – a major stimulus to develop the newer huge detectors Start of the main GZK fall, near 6x1019 eV Cosmic microwave background photons, with Lorentz shift of 6x1010  + p  p + π etc There seems to have been a problem in deducing the energy of the cosmic ray particle correctly --- and it has not entirely gone away

4. 1 | THE GZK HUNT 2 | 3 | 4| 5 The integral energy spectrum Shows that for a specified flux (particles per m2 per s per steradian) The older experiments, e.g. AGASA (AGA), Haverah Park (HPk), were attributing much higher energies 57 EeV than the Auger (PAO) and HiRes (HiR) observatories do. (even after a later revision of the Haverah Park energy assignments)

5. 1 | 2 | BEREZINSKY  UHE spectrum of PROTONS |3 | 4| 5 (2) BEREZINSKY ARGUES* FOR PROTON-DOMINATED UHE SPECTRUM, AS  + p  p + e+ + e-REACTION EXPLAINS SHAPE OF “ANKLE” VB  If primary protons have injection spectrum dN/dE  E-2.7 (for E>Ebreak) the spectrum has a hollow near the “ankle”-- & shape fitted many published spectra -- though other spectral slopes acceptable if (e.g.) sources evolve strongly. I had suggested this interpretation of the “ankle” in 1967 *, in the context of evolution of source power. But later, in 2005, Venya objected that I was then going astray, by including other C.R. nuclei, --- I am grateful to him for redirecting me to more profitable work ! (*VB’s study was much more detailed) * V. Berezinsky, A Gazizov & S. Grigorieva, Phy. Rev. D74 (2006) 0403005

6. 1 | 2 | BEREZINSKY  UHE spectrum of PROTONS |3 | 4| 5 (2) BEREZINSKY ARGUES FOR PROTON-DOMINATED UHE SPECTRUM, AS  + p  p + e+ + e-REACTION EXPLAINS SHAPE OF “ANKLE” VB  If primary protons have injection spectrum dN/dE  E-2.7 (for E>Ebreak) the spectrum has a hollow near the “ankle”-- & shape fitted many published spectra -- though other spectral slopes acceptable if (e.g.) sources evolve. I had suggested this interpretation of the “ankle” in 1967 *, in the context of evolution of source power. But later, in 2005, Venya objected that I was then going astray, by including other C.R. nuclei, --- I am grateful to him for redirecting me to more profitable work ! (*VB’s study was much more detailed) (T=3) 1967

7. 1 | 2 | BEREZINSKY  UHE spectrum of PROTONS |3 | 4| 5 How the main cosmic-ray components would fit together (i) Galactic components This shows that the total flux of Galactic (“SNR”) cosmic rays is expected to drop quite rapidly after 1017 eV -- though it may perhaps not fall off quite as steeply as shown here (guided by simplified models and by KASCADE), if there are are enough very high-speed low-mass SN ejections. Presumed extragalactic  CR from SNR 

8. 1 | 2 | BEREZINSKY  UHE spectrum of PROTONS |3 | 4| 5 pion production E-2.3 Flux without E losses A VARIANT ON BEREZINSKY’SFIT --- pair-production losses Spectrum of protons after struggling through the microwave treacle: S normalised here (apologies !) SF has more emphasis on fitting Galactic CR at low E: & on evolving sources W C If initial spectrum dN/dE ~ E-2.3, Production rate in universe: SF = like Porciani-Madau star formation rate SF2;C=constant; W=PM0.5;S= PM1.5 The (e+e-)energy losses in CMBR produce an ANKLE in right place.

9. 1 | 2 | BEREZINSKY  UHE spectrum of PROTONS |3 | 4| 5 And this is the flux that reaches us if one starts with He or O nuclei instead if protons: they also suffer nuclear fragmentation. (Reaction thresholds at different place.) The energy losses do not produce the required ankle. It is very difficult to get a spectrum like we observe if the original particles include many nuclei heavier than H – BUT. . . .

10. 1 | 2 | BEREZINSKY  UHE spectrum of PROTONS |3 | 4| 5 (ii) Galactic & extragalactic parts “second knee” If extragalactic sources provide a pure proton input ( E–2.3 ; SF form of evolution raised to power 1.25) , adding the SNR cosmic rays (knee graph), the total flux is well explained. Hence no Gal. outflow detected EG G (EG strength normalised at 1019 eV) Best fit (shown) is with 5%* of normal proportions of He and heavier nuclei and a slight raising* of the SNR tail. (*not really significant) Other evidence  “second knee” (HiRes);particle mass (Xmax) 

11. 1 | 2 | BEREZINSKY  UHE spectrum of PROTONS |3 | 4| 5 p predicted (If the primary particle is a large nucleus, the individual nucleons have less energy and their showers die out at a lesser atmospheric depth.) He Have primary protons ended early? C Equivalent mass The xmax test (depth of maximum of extensive air shower) Here, “xmax”– a – b.logE is plotted to make the line horizontal if the nuclear mass is unchanged with energy. (b is the “elongation rate”; a is arbitrary.) (Line is “best spectrum fit” 5%-of-normal He and metals.) The older pioneering “Stereo Fly’s Eye” data look discordant: there does appear to be a rapid change to light nuclei here.

12. 1 | 2 | 3 Auger 2007: A NEW KIND OF ANISOTROPY | 4| 5 (3) THE CHALLENGE AND EXCITEMENT OF AUGER 2007: A NEW KIND OF ANISOTROPY? The Auger data to August 2007 showed a new kind of pervasive fine-scale anisotropy: a close match of the directions of cosmic rays above 57 EeV to the directions of optically-detected AGNs (really to AGN clusters) – and an even more significant match to (not all) extended radio galaxies. “Anisotropy” can be much less boring than in the old days of 5% “first harmonics” I am aware that in recent runs, a completely different sky pattern has been recorded (details not yet available) but PLEASE “SUSPEND YOUR DISBELIEF” FOR THE NEXT 15 MINUTES while I entertain you with a remarkable story

13. 1 | 2 | 3 Auger 2007: A NEW KIND OF ANISOTROPY | 4| 5 BLUE zone Well . observed CEN A Aitoff Plot (very bright radio - - galaxy) Arrival directions of 27 particles above 5.7x1019 eV (Auger collabn) ٠Positions of 442 AGN within 75 Mpc 3.2º circles: 20/27 contain an AGN  A new kind of (small-scale) anisotropy This deserves more informative kinds of plot! (a) Uniform-exposure polar plot; (b) R.A. pattern resonance

14. 1 | 2 | 3 Auger 2007: A NEW KIND OF ANISOTROPY | 4| 5 R.A. Virgo cluster  Cosmic ray Optical AGN (Veron-Cetty & Veron) Extended radio galaxies - - typ. FRI (Nagar & Matulich) Supergalactic plane Galactic plane (really looks like a great circle) Uniform-exposure polar plot The cosmic ray directions would be spread uniformly within this circular diagram if they arrived isotropically. (because of suitable nonlinear choice of radial declination scale)

15. 1 | 2 | 3 Auger 2007: A NEW KIND OF ANISOTROPY | 4| 5 Quantitative use of uniform-exposure polar plot divided into 50 equal areas Numbers of VCV AGNs in each segment* (within 75 Mpc) weighted by exposure & rounded 9 of 50 segments (N>6) contain half the AGNs *Galactic obscuration zone ignored They also contain half the CRs * NCR / wtedNAGN = 0.1 in general

16. 1 | 2 | 3 Auger 2007: A NEW KIND OF ANISOTROPY | 4| 5 Counting AGNs in 3.2 “windows” around C.R. is an ingenious and unexpected approach, but --  These close “AGNs” often very feeble objects but patterns suggest CR scattered ~3-4; AGNs are clustered – nearest AGN will often not be the source --- The source is probably some object in the cluster  Optimization of radius stimulated doubts about significance (change 3.1  3.2 changed count) Any change of circumstances would require different radius * * --- SO I PROPOSE A SLIGHTLY DIFFERENT APPROACH

17. 1 | 2 | 3 Auger 2007: A NEW KIND OF ANISOTROPY | 4| 5 Aim 1:To measure closeness of cosmic rays to AGNs without having to use a “window” radius (such as 3.2) .● ● ● ● ● ● ● ● ● ● ● d1 d1 WHAT IS <d1> ? Measure of closeness of cosmic ray directions to AGNs by distance d1 to nearest AGN (degrees) Calculate average d1 for all the cosmic rays not within 12 of galactic plane (AGNs obscured)  2.2, cf 7 for isotropic CR Aim 2: To persuade ourselves there is a real association  without elaborate statistical argument. DISPLACE THE AGN & C.R. PATTERNS (rotate in R.A.)

18. 1 | 2 | 3 Auger 2007: A NEW KIND OF ANISOTROPY | 4| 5 Measuring closeness of cosmic ray directions to AGNs by mean distance <d1> (degrees) to nearest AGN .● ● ● ● ● ● ● ● ● ● ● d1 d1 <d1>~ 7 for isotropic CR * Using C.R. >12 from Gal. plane All 21 such cosmic rays  <d1> as AGNs are shifted in right ascension by Δ “Right ascension resonance” The CR, AGN have to be in their correct position to match  not an accident

19. 1 | 2 | 3 Auger 2007: A NEW KIND OF ANISOTROPY | 4| 5 Did the optimization of the “cuts” generate a spurious apparent association? .● ● ● ● ● ● ● ● ● ● ● d1 d1 <d1>~ 7 for isotropic CR * Using C.R. >12 from Gal. plane 11 cosmic rays after “cuts” selected  <d1> as AGNs are shifted in right ascension by Δ “Right ascension resonance”

20. 1 | 2 | 3 Auger 2007: A NEW KIND OF ANISOTROPY | 4| 5 Did the optimization of the “cuts” generate a spurious apparent association? .● ● ● ● ● ● ● ● ● ● ● d1 d1 <d1>~ 7 for isotropic CR * Using C.R. >12 from Gal. plane 11 cosmic rays after “cuts” selected  10 cosmic rays used for optimization  <d1> as AGNs are shifted in right ascension by Δ “Right ascension resonance” COUNTS in windows were biased . but <d1> is not

21. 1 | 2 | 3 Auger 2007: A NEW KIND OF ANISOTROPY | 4| 5 There are other AGNs with which CR might be correlated: 10 “extended radio galaxies”(within 75 Mpc again) using classification of Nagar & Matulich – mostly FRI or similar. -- very sparse on the sky Again a resonance at 0 offset with <10-5 chance probability All 27 cosmic rays: d1 from extended radio galaxies within 75 Mpc More: correlation seems to extend to 112 Mpc: 12 ERG in all & 10-12 CRs seem to be associated ~ 1 CR per radio-gal: a few have 2; a few have 0 (incl. Cen A?) contrast: ~0.1 CR per optical AGN but only 30-40% of CR from ext radiogal “Right ascension resonance”

22. 1 | 2 | 3 Auger 2007: A NEW KIND OF ANISOTROPY | 4| 5 Gross improbability of these patterns matching by accident ! (not even if cosmic rays are NOT isotropic, but come from a broad band of sky)

23. 1 | 2 | 3 Auger 2007: A NEW KIND OF ANISOTROPY | 4| 5 Most sources of cosmic rays with E > “57 EeV” on arrival seem to be within 100-120 Mpc. but protons would only drop below this threshold energy within this distance if Ethresh is really ~ 25% higher than quoted.  E scale is not yet right ? (and maximum source energy-per-nucleon may be not far above 110 EeV for most sources) ?? ---- but this question is complicated by possible effects of fragmentation of initially heavier nucleus.

24. 1 | 2 | 3 |4 Older experiments are still relevant | 5 (4) EARLIER EXPERIMENTS ARE STILL RELEVANT HiRes found no association with AGNs -- was this because a 3.2 window was inappropriate? or is the northern sky different? --- Haverah Park used similar detectors to Auger; but at lower energy -- is there anything still to learn from that?

25. 1 | 2 | 3 |4 Older experiments are still relevant | 5 HiRes 11 HiRes cosmic rays above 1.1x56 EeV on HiRes scale  (excluding low galactic latitudes) There is indeed no sign of a resonance at 0 (and CR unrelated to AGNs on uniform-exposure plot) Right ascension resonance

26. 1 | 2 | 3 |4 Older experiments are still relevant | 5 Haverah Park (again compared with optical AGNs within 75 Mpc) 11 Haverah Park CR above energy ? 70 EeV on scale then used, but - possibly ~32 “Auger EeV”  about 2% chance of accidental dip. I don’t have radio-galaxy positions to check, but . . . . 2 “standard” 3.2 windows each contain > 10 AGNs within 124 Mpc ! (one is centred on M87 in Virgo cluster) WHAT DO WE MAKE OF THIS? The HiRes/Auger difference is more likely to relate to a difference of technique than to a difference of sky hemisphere.

27. 1 | 2 | 3 |4 Older experiments are still relevant | 5 The integral energy spectrum and energy intercalibration Haverah Park “70 EeV” was revised downwards (2001) to ~50 EeV --- but the integral flux matches Auger flux at ~”32 Auger EeV” ---- perhaps ~40 EeV (later) 57 EeV

28. 1 | 2 | 3 |4 | 5 A challenge & enormous promise (5) A CHALLENGING PROBLEM – and ENORMOUS PROMISE A great encouragement to continue -- We have had a glimpse of the sources (The improbability of these AGN associations occurring by accident is too great to be credible) The challenge -- Conditions for strong association are unclear: not simply “>57 EeV” Rapid weakening below 57 EeV too sudden to be just GZK effect, I think -- more probably related to heavy nuclei that are prominent - in a limited range of energy -- and more opportunities could be close 

29. 1 | 2 | 3 |4 | 5 A challenge & enormous promise The challenge -- Conditions for strong association are unclear: not simply “>57 EeV” Non-protons would have much bigger deflections ( Z) (and very light nuclei are photodisintegrated VERY rapidly)  How do we isolate the protons? Old array experiments --AGASA, Haverah Park (not Yakutsk?) – recorded too many showers at the highest energy -- probably large fluctuations in estimated E  protons most likely? Auger may well have a similar problem: very slight changes may allow more or fewer p showers to be promoted to E above E of heavies. The appearance of a distinct proton group “above 57 EeV” may have been a “happy accident”! -- But more opportunities could be close 

30. 1 | 2 | 3 |4 | 5 A challenge & enormous promise More opportunities could be close • Types of source: • Should get a few CRs from each of several radio galaxies • Critical jet power to generate such CR • (radio-galaxies seemed to supply only ~ 40%) Galactic halo magnetic field should deflect CR For 9 Auger CRs (>57 EeV) arriving in limited range of galactic latitude and longitude, the resonance appears to be shifted ~ 4 4 (would imply Bz x path length ~0.3μG x 20kpc “downwards”)

31. 1 | 2 | 3 |4 | 5 A challenge & enormous promise A great encouragement to continue -- -- to Venya, who has already guided us in this field for so long: Life does not stop at 75 ! (though it gets harder) Note: see arXiv [astro-ph.HE]: 0906.0280 for more details of material presented here

32. END

33. AGASA (again compared with optical AGNs within 75 Mpc) 100 EeV on scale then used, but - possibly ~48 “Auger EeV” 7 AGASA CR above energy ?  about 14% chance of accidental dip. Right ascension resonance

34. 1 | 2 | BEREZINSKY  UHE spectrum of PROTONS |3 | 4| 5