1. Heraeus-400 11 Feb. 2008 Tom Gaisser1 Particle Astrophysics Some questions to consider during this meeting

2. Heraeus-400 11 Feb. 2008 Tom Gaisser2 F( ) for cosmic rays LHC Tevatron DIRECT Air Showers Extra-galactic component ?

3. Heraeus-400 11 Feb. 2008 Tom Gaisser3 Energetics of cosmic rays Total local energy density: –(4  /c) ∫ E  (E) dE ~ 10 -12 erg/cm 3 ~ B 2 / 8  Power needed: (4  /c) ∫ E  (E) /  esc (E) dE galactic  esc ~ 10 7 E -0.6 yrs Power ~ 10 -26 erg/cm 3 s Supernova power: 10 51 erg per SN ~3 SN per century in disk ~ 10 -25 erg/cm 3 s SN model of galactic CR Power spectrum from shock acceleration, propagation Spectral Energy Distribution (linear plot shows most E < 100 GeV) (4  /c) E  (E) = local differential CR energy density

4. Heraeus-400 11 Feb. 2008 Tom Gaisser4 Supernova progenitor SN ejecta Shocked ISM Acceleration by supernova remnants the ‘standard model’ of cosmic-ray origin Unshocked ISM SNR expands into ISM with velocity V~ 10 4 km/s. Drives forward shock at 4/3 V Forward shock u 1 ~ 4/3 V Particle with E 1 E 2 =  E 1 Contact discontinuity, V T SN ~ 1000 yrs before slowdown E max ~ Z x 100 TeV

5. Heraeus-400 11 Feb. 2008 Tom Gaisser5 Problems of simplest SNR shock model Expected shape of spectrum : –Differential index  ~ 2.1 for diffusive shock acceleration  observed ~ 2.7  source ~2.1;  ~ 0.6   esc (E) ~ E -0.6 c  esc  T disk ~100 TeV  Isotropy problem E max ~  shock Ze x B x R shock –  E max ~ Z x 100 TeV with exponential cutoff of each component –But spectrum continues to higher energy:  E max problem Expect p + gas   (TeV) for certain SNR –Need nearby target as shown in picture from Nature ( April 02) –Some likely candidates (e.g. HESS J1745-290) but still no certain example –  Problem of elusive  0  -rays

6. Heraeus-400 11 Feb. 2008 Tom Gaisser6 Leptonic vs. hadronic models of SNR RX J1713-3946 HESS collaboration, A&A 449, 2006 Hadronic broadband model: Berezkho & Völk, 2006 Critical issue: B-field

7. Heraeus-400 11 Feb. 2008 Tom Gaisser7 Chandra Cassiopeia A Chandra SN 1006 Filamentary structure of X-ray emission of young SNRs: Evidence for amplification, B ~ 100  G Berezhko&Volk, OG111

8. Heraeus-400 11 Feb. 2008 Tom Gaisser8 Shock acceleration non-linear case Spectrum at shock concave,  < 2 at high energy, energy concentrated at Emax Amato & Blasi, MNRAS 371 (2006) 1251 Numbers are far-upstream shock velocity Linear case (neglect CR pressure)  = 2 for dN / dE (q = 4 for dN / d 3 p)

9. Heraeus-400 11 Feb. 2008 Tom Gaisser9 Shock acceleration - 2 Cosmic-ray pressure also amplifies magnetic field (Bell, MNRAS 353, 550, 2004) E max increases to 10 16 or 10 17 eV in early, free-expansion phase of SNR expansion applies to small fraction of accelerated particles ALSO (Ptuskin & Zirakashvili, A&A 429, 755, 2005 ) In later phases of SNR expansion: - upstream scattering becomes inefficient as expansion slows down - E max  E max (t) decreases with time - Accelerated particles with E > E max (t) escape upstream - observed spectrum is integral of SNR history - may vary from one SN to the next

10. Heraeus-400 11 Feb. 2008 Tom Gaisser10 Wanted – a global model of galactic cosmic rays How many supernovae contribute to the observe population of galactic cosmic rays? What is their variety (Emax, spectrum, environment, plerions, shell type, SN with massive progenitors …)? What is the effect of propagation?

11. Heraeus-400 11 Feb. 2008 Tom Gaisser11 Lessons from the heliosphere Coronal mass ejection 09 Mar 2000 09 Mar 2000

12. Heraeus-400 11 Feb. 2008 Tom Gaisser12 Solar flare of Dec 13, 2006 Observation by PAMELA Satellite Experiment Galactic CR suppressed by plasma blast Solar energetic particles

13. Heraeus-400 11 Feb. 2008 Tom Gaisser13 LASCO event of 23 Nov 97 http://lasco-www.nrl.navy.mil/best_of_lasco_apr98/index.htm

14. Heraeus-400 11 Feb. 2008 Tom Gaisser14 ACE: sum of solar events Fluence of Oxygen in 3 years Smooth spectrum –composed of several distinct components: Most shock accelerated Many events with different shapes contribute at low energy (< 1 MeV) Few events produce ~10 MeV –Knee ~ Emax of a few events –Ankle at transition from heliospheric to galactic cosmic rays R.A. Mewaldt et al., A.I.P. Conf. Proc. 598 (2001) 165

15. Heraeus-400 11 Feb. 2008 Tom Gaisser15 Heliospheric cosmic rays ACE--Integrated fluences: –Many events contribute to low-energy heliospheric cosmic rays; –fewer as energy increases. –Highest energy (75 MeV/nuc) is dominated by low-energy galactic cosmic rays, and this component is again smooth Beginning of a pattern? R.A. Mewaldt et al., A.I.P. Conf. Proc. 598 (2001) 165

16. Heraeus-400 11 Feb. 2008 Tom Gaisser16 Power laws occur in many contexts (M.E.J. Newman, cond-mat/0412004)

17. Heraeus-400 11 Feb. 2008 Tom Gaisser17 Casualties per attack in Iraq (Neil F. Johnson, et al., from APS News, 8 Nov 2006) Differential  ~ 2.5

18. Heraeus-400 11 Feb. 2008 Tom Gaisser18 Berezhko & Völk: global fit to data with Emax = Z x 3 x 10 15 eV Problem is hard source spectrum:  source < 2 requires  esc ~ E -  with  ~ 0.75 to compensate hard (concave) source spectrum Observed isotropy is a problem --made worse by harder spectrum Also note He spectrum is harder than protons ?? arXiv 0704.1715  observed = 2.7 =  source + 

19. Heraeus-400 11 Feb. 2008 Tom Gaisser19 KASCADE: Energy spectra for elemental groups T. Antoni et al., Astropart. Phys. 24 (2005) 1 (Slide from J. Hörandel at RICAP07 Knee caused by cut-off for light elements Astrophysical interpretation limited by description of interactions in the atmosphere

20. Heraeus-400 11 Feb. 2008 Tom Gaisser20 Muon content of > EeV events Auger: Engel et al., ICRC07 arXiv:0706.1921 (astro-ph)

21. Heraeus-400 11 Feb. 2008 Tom Gaisser21 Question about models Both SIBYLL and QGSjet-II appear to produce too few muons for protons –Are EeV showers all Fe or heavier? –Is there a problem with the models?

22. Heraeus-400 11 Feb. 2008 Tom Gaisser22 Heavies at end of galactic Extra-galactic protons Berezhko & Völk arXiv:0704.1715v1 [astro-ph] Model galactic component Subtract from observed to get extragalactic Transition predicted: 10 16.5 to 10 17.5 eV

23. Heraeus-400 11 Feb. 2008 Tom Gaisser23 Allard, Olinto, Parizot, astro-ph/0703633 Or start with a model of the extra- galactic component Subtract it from the observed spectrum to get the galactic component What is power needed for extra-galactic CR? 3 x 10 17 eV 3 X 10 18 eV

24. Heraeus-400 11 Feb. 2008 Tom Gaisser24 Power needed for extragalactic cosmic rays assuming transition at 10 19 eV Energy density in UHECR,  CR ~ 2 x 10  erg/cm 3 –Such an estimate requires extrapolation of UHECR to low energy –  CR = (4  /c)  E  (E) dE = (4  /c){E 2  (E)}  E=10 19 eV x ln{E max /E min } –This gives  CR ~ 2 x 10  erg/cm 3 for differential index  = 2,  (E) ~ E -2 Power required ~  CR /10 10 yr ~ 1.3 x 10 37 erg/Mpc 3 /s –Estimates depend on cosmology and assumed spectral index: –3 x 10 -3 galaxies/Mpc 3 5 x 10 39 erg/s/Galaxy –3 x 10 -6 clusters/Mpc 3 4 x 10 42 erg/s/Galaxy Cluster –10 -7 AGN/Mpc 3 10 44 erg/s/AGN –~1000 GRB/yr 3 x 10 52 erg/GRB

25. Heraeus-400 11 Feb. 2008 Tom Gaisser25 Active Galactic Nuclei as cosmic accelerators? Auger Collaboration: 20 of 27 events with E > 57 EeV are within 3.1 degrees of an AGN less than 75 Mpc away. Centaurus-A (4 Mpc, white dot) is especially prominent. ( 57 EeV = 0.01 Joule ) ( 1 Mpc = 3 million light years )

26. Heraeus-400 11 Feb. 2008 Tom Gaisser26 Accretion and astrophysical jets VLA image of Cygnus A An active galaxy A common phenomenon on both stellar & galactic scales: Matter falls onto black hole or neutron star driving collimated, relativistic jets perpendicular to the disk

27. Heraeus-400 11 Feb. 2008 Tom Gaisser27 AGN model of UHECR Jörg Rachen & Peter Biermann, A&A 272 (1993) 161 Note potential effect at low energy of strong cosmological evolution of sources. First pointed out by Michael Hillas at 1967 ICRC (Can. J. Phys. 46 (1968) S623-S626) Fits depend on Emax & spectral index Softer spectrum requires more power

28. Heraeus-400 11 Feb. 2008 Tom Gaisser28 HiRes observation of GZK cutoff D. Bergman et al., astro-ph/0609431 p +   e + e - + p this process gives a dip for E ~ 10 19 eV if extra-galactic C.R. are protons (Berezinsky et al.) Look for a change in composition to find transition between two populations, galactic and extra-galactic Energy loss via  p +   n +  +  and  + + 

29. Heraeus-400 11 Feb. 2008 Tom Gaisser29 Composition with air showers Proton penetrates deep in atmosphere –Shower max deeper –( mu / e ) smaller – muons start deeper Heavy nucleus cascade starts high – shower max higher up –( mu / e ) larger – muons start higher proton heavy nucleus

30. Heraeus-400 11 Feb. 2008 Tom Gaisser30 Composition with air shower experiments Sketch of ground array with fluorescence detector – Auger Project Telescope Array realize this concept Km scale detectors: PeV to EeV  1000 Km 2 detectors: > EeV  Auger & Telescope Array Planning low energy extensions  / e Xmax

31. Heraeus-400 11 Feb. 2008 Tom Gaisser31 Where is transition to extragalactic CR? Original Fly’s Eye (1993): transition coincides with ankle 3 EeV G. Archbold, P. Sokolsky, et al., Proc. 28 th ICRC, Tsukuba, 2003 HiRes new composition result: transition occurs before ankle or 0.3 EeV ?

32. Heraeus-400 11 Feb. 2008 Tom Gaisser32 X max by Auger M. Unger, Auger, arXiv: 0706.1495 Comparison with updated HiRes data made by M. Teshima, rapporteur, ICRC2007

33. Heraeus-400 11 Feb. 2008 Tom Gaisser33 Questions Are the highest energy showers also heavy? –If so, how can they point to AGNs despite bending in intervening magnetic fields? –If not, either Xmax vs E must change drastically above 40 EeV Or Xmax calculation is wrong Or…

34. Heraeus-400 11 Feb. 2008 Tom Gaisser34 Cosmic-ray physics with IceCube Photo: James Roth 17/12/07

35. Heraeus-400 11 Feb. 2008 Tom Gaisser35 Reconstructed assuming Fe Reconstructed assuming p IceTop only Spectrum Reconstructed assuming mixed Stefan Klepser preliminary Note: lightly shaded points are in threshold region where results of unfolding algorithm are not meaningful

36. Heraeus-400 11 Feb. 2008 Tom Gaisser36 Multi-messenger astronomy Cosmic rays Neutrinos TeV  -rays

37. Heraeus-400 11 Feb. 2008 Tom Gaisser37 neutrinos from GZK interactions galactic extragalactic Slide by Francis Halzen, ICRC07

38. Heraeus-400 11 Feb. 2008 Tom Gaisser38 Question: challenge How can we measure GZK neutrinos? –To confirm spectral steepening is in fact due to absorption of UHECR by CMB –How good does the measurement have to be to tell us something about early epochs of UHE cosmic-ray accelerators (Z > 1)? –Problem: expected rate ~1 event / km 3 / yr –Goal: >1000 km 3 sr, > 100 events/yr, E >10 18 eV –Radio detection, e.g. RICE, ANITA … –Acoustic detection in Ice another possibility

39. Hadronic vs e-m model of AGNs Markarian 501 flare observed by MAGIC Time lag of 4.1 minutes between lowest and highest energy band If interpreted as reflection of acceleration time could favor SSC model over hadronic model? SSC fit to Mrk 421 Konopelko, Ap.J. 597 (2003) 851 Hadronic cascade fit to Mrk 421 Mücke et al., Astropart.Phys. 18 (2003)

40. Heraeus-400 11 Feb. 2008 Tom Gaisser40 Questions If UHECR come from AGN –Where are they accelerated? In the base of the jets where TeV gamma-ray originate? or Far out in the termination shock? –What are the implications for TeV neutrinos? –Normalize to Auger UHECR flux from Cen A < 1 event per km 3 year from single source Diffuse signal from all similar sources ~ 0.1 x W-B –Halzen & Murchadha, arXiv:0802.0887

41. Heraeus-400 11 Feb. 2008 Tom Gaisser41 Waxman-Bahcall bound -- can it be realized ? One generic model: Cosmic accelerator accelerates protons Magnetic fields contain protons for  accel Environment contains photons of density n   or gas) If  diffusion >  collision = 1/ ( c  p   n   and If source size < 1/ (  p   n   Protons photoproduce neutrons & pions Neutrons escape and decay to become cosmic rays Pions decay:  ±  ;  0  

42. Heraeus-400 11 Feb. 2008 Tom Gaisser42 TeV sources in the Galactic plane Jim Hinton Rapporteur at ICRC 2007 Cygnus Region MILAGRO

43. Heraeus-400 11 Feb. 2008 Tom Gaisser43 Can neutrinos from Galactic TeV gamma-ray sources be detected?

44. Heraeus-400 11 Feb. 2008 Tom Gaisser44 Concluding comments After 96 years since Hess’ discovery, the time is ripe to make a global picture of sources and origin of galactic cosmic rays –The pieces just need to be assembled Prospects are hopeful for UHECR in light of recent Auger results on anisotropy A key task is to map the transition by measuring composition from PeV to EeV