Ultra-High Energy Cosmic Rays and the GeV-TeV Diffuse Gamma-Ray Flux

Transcription

1 The 4th International Workshop on The Highest Energy Cosmic Rays and Their Sources INR, Moscow May 20-22, 2008 Ultra-High Energy Cosmic Rays and the GeV-TeV Diffuse Gamma-Ray Flux Oleg Kalashev* (INR RAS) co-authors: D.Semikoz, G.Sigl * kalashev@ms2.inr.ac.ru

2 Ultra-High Energy Cosmic Rays and the GeV-TeV Diffuse γ-ray Flux Overview Propagation of Ultra High Energy Cosmic Rays (UHECR) Source model and spectrum fitting Possible range of diffuse γ-ray flux from protons Diffuse γ-ray flux from heavy nuclei. Comparison Conclusion

3 Propagation of Ultra High Energy Cosmic Rays Protons and neutrons Pion production N γ b N p e + e - pair production p γ b pe + e - neutron β-decay n pe ν e

4 Propagation of Ultra High Energy Cosmic Rays Protons and neutrons Pion production N γ b N p E th = m π(m p +m π /2) ² ' 7 16 ( ² ev ) 1 ev For MWB (² ' 3 ev ): E th ' 70EeV (1) e + e - pair production p γ b pe + e - neutron β-decay n pe ν e

5 Propagation of Ultra High Energy Cosmic Rays Protons and neutrons Pion production N γ b N p E th = m π(m p +m π /2) ² ' 7 16 ( ² ev ) 1 ev (1) For MWB (² ' 3 ev ): E th ' 70EeV e + e - pair production p γ b pe + e - E th = m e(m A +m e ) ² ' 5 14 ( ² ev ) 1 ev neutron β-decay For MWB (² ' 3 ev ): E th ' 5 17 ev n pe ν e (2)

6 Propagation of Ultra High Energy Cosmic Rays Protons and neutrons Pion production e + e - pair production N γ b N p p γ b pe + e - neutron β-decay n pe ν e Electron-photon cascade e, γ e + e - pair production γγ b e + e - Inverse Compton e γ b e γ E th = m2 e ² ' ( ² ev ) 1 ev For MWB (² ' 3 ev ): E th ' 5 14 ev

7 Propagation of Ultra High Energy Cosmic Rays Protons and neutrons Pion production e + e - pair production N γ b N p p γ b pe + e - neutron β-decay n pe ν e Electron-photon cascade e, γ e + e - pair production γγ b e + e - Inverse Compton e γ b e γ Synchrotron losses Double pair production γγ b e + e - e + e - e + e - pair production by e e γ b ee + e -

8 Propagation of Ultra High Energy Cosmic Rays Nuclei Pion production A γ b A p e + e - pair production A γ b Ae + e - Photo-disintegration A γ b A N.. Protons and neutrons Pion production N γ b N p p, n e, γ e + e - pair production p γ b pe + e - neutron β-decay Electron-photon cascade n pe ν e e, γ

9 Propagation of Ultra High Energy Cosmic Rays Energy loss length of Fe and protons A γ b A p e + e - pair production A γ b Ae + e - Photo-disintegration A γ b A N.. Protons and neutrons p Pion production N γ b N p p, n e, γ Fe e + e - pair production p γ b pe + e - e, γ Electron-photon cascade

10 Some references on UHECR propagation p production Photodisintegration e + e pair production Extragalactic magnetic field Infrared background Radio background A.Mucke et al.,comp.phys.comm.124,290(2000) F.Stecker et al. Astrophys.J. 512 (1999) E.Khan et al. Astropart.Phys. 23 (2005) M.J.Chodorowski et al. Astrophys.J.400,181(1992) K.Dolag et al., astro-ph/04419 F.Stecker et al. astro-ph/05449 T.A. Clark, L.W. Brown, and J.K. Alexander, Nature 228, 847 R.J. Protheroe, P.L. Biermann, Astropart. Phys. 6, 45

11 Phenomenological source model: F A(p) (E, z) = f E -α (1+z) 3+m Θ(E max -E) Θ(z-z min ) Θ(z max -z) z red shift, Θ(x)-step function Parameter Name Values Power of the Injection Spectrum, E -α α 2.0 α 2.7 End point of the Energy Spectrum E max 2x 20 E max 21 Evolution factor: (1+z) 3+m m -2 m 4 Red shift of the nearest source z min 0; 0.005; 0.01 Maximal source redshift z max 3

12 Fitting procedure For each set of parameters we dip scenario F(E, z) = f E -α (1+z) 3+m Θ(E max -E) Θ(z-z min ) Θ(z max -z) Calculate propagated spectrum Obtain normalization factor f by fitting HiRes spectrum (maximizing Poisson probability of measured events configuration using number of events in each bin*) Calculate goodness of fit defined as fraction of hypothetical experiments which result in worse agreement with the theory than the real data but have the same total number of events Among all the models we choose a subset which has goodness of fit more than 5% and for this subset we check the range of possible diffuse γ-ray flux We use two scenarios for fitting: The fit is done above 2 EeV ankle scenario The fit is done above 40 EeV *HiRes Mono spectrum including number of events in each bin

13 Fitting procedure F(E, z) = f E -α (1+z) 3+m Θ(E max -E) Θ(z-z min ) Θ(z max -z) dip scenario ankle scenario j(e)e 2 [ev cm s sr ] EGRET p HiRes p inj j(e)e 2 [ev cm s sr ] EGRET p HiRes p inj E ev α=2.45; E max = 21 ev; m= E ev α=2; E max = 21 ev; m=

14 Diffuse Gamma-Ray Flux from protons Contribution of e + e - production and GZK effect dip scenario ankle scenario j(e) E 2 [ev cm -2 s -1 sr -1 ] EGRET γ from π 0, no e + e - γ from π 0 and e + e - p HiRes p inj j(e) E 2 [ev cm -2 s -1 sr -1 ] EGRET γ from π 0, no e + e - γ from π 0 and e + e - p HiRes p inj E [ev] E [ev]

15 F UHECR /F EGRET Diffuse Gamma-Ray Flux Dependence on the initial spectrum F A(p) (E, z) = f E -α (1+z) 3+m Θ(E max -E)Θ(z-z min ) Θ(z max -z) Dip scenario Ankle scenario m Fraction (predicted to EGRET) of integral fluxes between 1 and 2 GeV Minimal and maximal value The contribution of secondary photons from protons is at least 1% in realistic models and it may be more than 50% for strong evolution (m > 3)

16 Diffuse Gamma-Ray Flux Dependence on initial proton spectrum F A(p) (E, z) = f E -α (1+z) 3+m Θ(E max -E)Θ(z-z min ) Θ(z max -z) 1 m=4 m<4 F UHECR /F EGRET -1-2 m= α

17 Diffuse Gamma-Ray Flux from protons compared with other possible astrophysical contributions 3 EGRET Star forming galaxies: V. Pavlidou and B. D. Fields, Astrophys. J. 575, L5 (2002) [arxiv:astro-ph/ ]. j(e) E 2 [ev cm -2 s -1 sr -1 ] 2 star-forming starburst galaxies Total AGN UHECR AGN evolution UHECR GRB structure formation AGN: C. D. Dermer, arxiv:astro-ph/ Starburst: T. A. Thompson, E. Quataert and E. Waxman, Astrophys. J. 654, 219 (2006) [arxiv:astro-ph/ ]. large scale structure formation shocks: U. Keshet, E. Waxman, A. Loeb, V. Springel and L. Hernquist, Astrophys. J. 585, ) [arxiv:astro-ph/ ] E [ev] γ ray bursts: C. D. Dermer, arxiv:astro-ph/06195

18 je 2 [ev sm sec sr ] Diffuse Gamma-Ray Flux from nuclei e + e - production by nuclei and p gives main contribution Secondary γ-ray flux can be as low as 0.1% of EGRET bound level Fit is done above 40 EeV E max = Z x 21 ; α = 2; AGN evolution EGRET γ from π ±0 γ total p HiRes Fe (Z=26) je 2 [ev sm sec sr ] E max = Z x 2 x 19 ; α = 2; m=0 ok with Auger, but not supported by composition studies of HiRes! 1 EGRET γ from π ±0 γ total p HiRes E ev E ev

19 Conclusions Protons contribute no less than 1% to the observed EGRET flux, and up to 50% in the case of strong source evolution Future measurements of resolved and unresolved components of the diffuse GeV-TeV γ ray background or upper limits on such components can give important information on UHECR origin and the distribution of their sources Nuclei sources are much less constrained in terms of diffuse gamma ray flux they produce

20 Appendix Sample transport equation for electrons (includes only pair production PP and inverse Compton scattering ICS)

21 References Original work on this subject HiRes spectrum O.Kalashev, D.Semikoz, G.Sigl, arxiv:astro-ph/ R. Abbasi et al. [HiRes Collaboration], arxiv:astro-ph/

22 Greisen-Zatsepin-Kuzmin (GZK) cutoff Interaction length on MWB approaches 6 Mpc ~20% of energy is carried away by pions in each interaction Threshold energy N γ N p N,N = p or n For MWB E th 4 x 19 ev

23 Energy loss lengths p and γ energy loss lengths (minimal RB assumed)

24 Deflection and synchrotron radiation Gyroradius: R g = E qeb ' q E 21 ev B 9 G 1 Mpc Synchrotron loss length: de dt = 4 3 σ T B2 qme 8π m 4 ³ 2 E m e E γ ' 3eB 2m e ³ Ee m e 2 ' E e 21 ev 2 B G ev 9 The gyroradii and the synchrotron loss rates of electrons for various strengths of the EGMF