Michael Hillas University of Leeds A tribute to Veniamin Berezinsky Old and new ways of looking at UHECRs. A happy accident? 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

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

1 | THE GZK HUNT 2 | 3 | 4| 5 and : 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 6x10 19 eV Cosmic microwave background photons, with Lorentz shift of 6x10 10   + 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

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

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>E break )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)

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>E break )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  )

This shows that the total flux of Galactic (“SNR”) cosmic rays is expected to drop quite rapidly after 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  1 | 2 | BEREZINSKY  UHE spectrum of PROTONS |3 | 4| 5 How the main cosmic-ray components would fit together (i) Galactic components

Spectrum of protons after struggling through the microwave treacle: If initial spectrum dN/dE ~ E -2.3, Production rate in universe: SF = like Porciani-Madau star formation rate SF2; C=constant; W=PM 0.5 ; S= PM 1.5 SF C W S normalised here The (e + e - )energy losses in CMBR produce an ANKLE in right place. pair-production losses pion production 1 | 2 | BEREZINSKY  UHE spectrum of PROTONS |3 | 4| 5 A VARIANT ON BEREZINSKY’S FIT --- (apologies !) has more emphasis on fitting Galactic CR at low E: & on evolving sources Flux without E losses E -2.3

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 | 2 | BEREZINSKY  UHE spectrum of PROTONS |3 | 4| 5

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. 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) (EG strength normalised at eV) G EG 1 | 2 | BEREZINSKY  UHE spectrum of PROTONS |3 | 4| 5 Other evidence “second knee” (HiRes);  particle mass (X max )  (ii) Galactic & extragalactic parts “second knee” Hence no Gal. outflow detected

(If the primary particle is a large nucleus, the individual nucleons have less energy and their showers die out at a lesser atmospheric depth.) The x max test (depth of maximum of extensive air shower) Here, “x max ”– a – b.logE is plotted to make the line horizontal if the nuclear mass is unchanged with energy. (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. p He C Equivalent mass (b is the “elongation rate”; a is arbitrary.) 1 | 2 | BEREZINSKY  UHE spectrum of PROTONS |3 | 4| 5 predicted Have primary protons ended early?

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) PLEASE “SUSPEND YOUR DISBELIEF” FOR THE NEXT 15 MINUTES while I entertain you with a remarkable story but

Arrival directions of 27 particles above 5.7x10 19 eV (Auger collab n ) ٠ Positions of 442 AGN within 75 Mpc (very bright radio - - galaxy) CEN A BLUE zone Well. observed 3.2º circles: 20/27 contain an AGN  A new kind of (small-scale) anisotropy 1 | 2 | 3 Auger 2007: A NEW KIND OF ANISOTROPY | 4| 5 Aitoff Plot This deserves more informative kinds of plot! (a) Uniform-exposure polar plot; (b) R.A. pattern resonance

1 | 2 | 3 Auger 2007: A NEW KIND OF ANISOTROPY | 4| 5 R.A. 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) Galactic plane (really looks like a great circle) Virgo cluster  Extended radio galaxies - - typ. FRI (Nagar & Matulich)  Cosmic ray  Optical AGN (Veron-Cetty & Veron) Supergalactic plane

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 They also contain half the CRs * *Galactic obscuration zone ignored N CR / wted N AGN = 0.1 in general

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 --  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  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

1 | 2 | 3 Auger 2007: A NEW KIND OF ANISOTROPY | 4| 5.● ● ● ● ● ● ● ● ● ● ● Measure of closeness of cosmic ray directions to AGNs by distance d 1 to nearest AGN (degrees) d1d1 Aim 1: To measure closeness of cosmic rays to AGNs without having to use a “window” radius (such as 3.2  ) Calculate average d 1 for all the cosmic rays not within 12  of galactic plane (  AGNs obscured)  2.2 , cf 7  for isotropic CR WHAT IS ? Aim 2: To persuade ourselves there is a real association  without elaborate statistical argument. DISPLACE THE AGN & C.R. PATTERNS (rotate in R.A.) d1d1

1 | 2 | 3 Auger 2007: A NEW KIND OF ANISOTROPY | 4| 5.● ● ● ● ● ● ● ● ● ● ● d1d1 ~ 7  for isotropic CR Measuring closeness of cosmic ray directions to AGNs by mean distance (degrees) to nearest AGN d1d1 All 21 such cosmic rays “Right ascension resonance”  as AGNs are shifted in right ascension by Δ  The CR, AGN have to be in their correct position to match  not an accident * Using C.R. >12  from Gal. plane

1 | 2 | 3 Auger 2007: A NEW KIND OF ANISOTROPY | 4| 5.● ● ● ● ● ● ● ● ● ● ● d1d1 ~ 7  for isotropic CR Did the optimization of the “cuts” generate a spurious apparent association? d1d1 11 cosmic rays after “cuts” selected “Right ascension resonance”  as AGNs are shifted in right ascension by Δ  * Using C.R. >12  from Gal. plane

1 | 2 | 3 Auger 2007: A NEW KIND OF ANISOTROPY | 4| 5.● ● ● ● ● ● ● ● ● ● ● d1d1 ~ 7  for isotropic CR Did the optimization of the “cuts” generate a spurious apparent association? d1d1 11 cosmic rays after “cuts” selected “Right ascension resonance”  as AGNs are shifted in right ascension by Δ  * Using C.R. >12  from Gal. plane 10 cosmic rays used for optimization COUNTS in windows were biased. but is not

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: d 1 from extended radio galaxies within 75 Mpc More: correlation seems to extend to 112 Mpc: 12 ERG in all & CRs seem to be associated ~ 1 CR per radio-gal: a few have 2; a few have 0 (incl. Cen A?) “Right ascension resonance” contrast: ~0.1 CR per optical AGN but only 30-40% of CR from ext radiogal

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)

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 Mpc. but protons would only drop below this threshold energy within this distance if E thresh 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.

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? 1 | 2 | 3 |4 Older experiments are still relevant | 5 (4) EARLIER EXPERIMENTS ARE STILL RELEVANT

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) HiRes 1 | 2 | 3 |4 Older experiments are still relevant | 5 Right ascension resonance

Haverah Park 11 Haverah Park CR above energy ?70 EeV on scale then used, but - possibly ~32 “Auger EeV”  about 2% chance of accidental dip. (again compared with optical AGNs within 75 Mpc) 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. I don’t have radio-galaxy positions to check, but | 2 | 3 |4 Older experiments are still relevant | 5 2 “standard” 3.2  windows each contain > 10 AGNs within 124 Mpc ! (one is centred on M87 in Virgo cluster)

The integral energy spectrum 57 EeV 1 | 2 | 3 |4 Older experiments are still relevant | 5 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) and energy intercalibration

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 

1 | 2 | 3 |4 | 5 A challenge & enormous promise The challenge -- Conditions for strong association are unclear: not simply “>57 EeV” -- But more opportunities could be close  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”!

1 | 2 | 3 |4 | 5 A challenge & enormous promise More opportunities could be close Types of source: (a)Should get a few CRs from each of several radio galaxies (b)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  (would imply B z x path length ~0.3μG x 20kpc “downwards”) 44

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]: for more details of material presented here

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

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