A few grams of matter in a bright world

Transcription

1 A few grams of matter in a bright world Benjamin Rouillé d Orfeuil (LAL) Fellow Collaborators: D. Allard, C. Lachaud & E. Parizot (APC) A. V. Olinto (University of Chicago) February 12 th 2013 LAL

2 All of our knowledge in astrophysics comes from the study of photons long story... CRs physics just started a century ago Key subject in astrophysics one of the main component of our galaxy (> 1 ev cm -3 ) CRs are not immutable! low-e: interaction with ISM high-e: interaction with radiation fields It affects both energy and mass spectra + production of secondary particles: photons, neutrinos, radioactive nuclei 2

3 Cosmic Rays Charged particles K. Kotera and A. V. Olinto, ARA&A (2012) power law spectrum and background radiation of CRs quasi-isotropic acceleration: diffusive shock propagation: magnetic fields 3

4 Astrophysical interpretation of UHECR data UHECRs observables at Earth Energy spectrum mass spectrum photon backgrounds angular spectrum EGMF GMF injected spectra composition CRs emissivity distribution of sources sources density 4

5 Main results: (i) energy spectrum log (E/eV) ev -2 yr -1 sr -1 J(E) [km ] sys (E)=22% 3 E HiRes Auger power laws power laws + smooth function Pierre Auger Collaboration, Phys. Lett. B (2010) Energy [ev] Two important features: ankle around ev suppression of the flux above ev 5

6 Main results: (ii) mass spectrum The change of <X max > per decade of E is sensitive to changes in composition with E The magnitude of the shower-toshower fluctuations of X max is also composition dependent ] 2 <X max > [g/cm QGSJET01 QGSJETII Sibyll2.1 EPOSv1.99 proton ] 2 ) [g/cm max RMS(X proton 700 iron iron Pierre Auger Collaboration, PRL (2010) E [ev] E [ev] Increasing average mass of the primary particles (assuming hadronic interaction properties don t change much) Limits on neutrinos and photons have been set 6

7 Main results: (iii) angular spectrum catalogue (relative exposure) 69 events > 55 EeV Pierre Auger Collaboration, Astropart. Phys. (2010) Anisotropic sky at the highest energies rejection of isotropy with 99% C.L 7

8 CR protons and nuclei interactions 8 Protons adiabatic losses pair production: P +! p + e e + low inelasticity process interaction with CMB ev pion production: large inelasticity process ( 20%) interaction threshold ev cosmogenic neutrinos: n +! n 0 + p +! n + + +! µ + µ + µ +! e + + e + µ p + e + e n +! p +! µ + µ µ! e + e + µ nuclei Two types of processes: decrease of the Lorentz factor adiabatic losses pair production: A ev photodissociation Giant dipole resonance (GDR) largest cross-section threshold MeV Quasi-Deuteron (QD) threshold 30 MeV pion production (BR) threshold 145 MeV cosmogenic neutrinos: pion production of secondary p and n; β-decay of secondary n decay of pions produced during BR

9 D. Allard, Astropart. Phys. (2012) D. Allard, Astropart. Phys. (2012) Proton attenuation length: expansion below ev pair production with CMB photons pion production ev strong decrease: GZK cut-off 9 Nuclei photodissociation mean free path: species have similar threshold for GDR in the NRF interaction threshold at same Γ energy threshold proportional to A cross-section proportional to A mean free path proportional to A GDR dominates at all energies but the very highest

10 D. Allard, Astropart. Phys. (2012) D. Allard, Astropart. Phys. (2012) Iron attenuation length: photodissociation processes dominates quite important role of pair production strong decrease above Γ , GDR with CMB GZK cut-off for nuclei Proton and nuclei attenuation length: similar shape for complex nuclei (same processes at work) shifted in energy different shape for protons (ankle) light nuclei suppression ev protons and heavy nuclei expected at the highest energies 10

11 The way out of the mist Only close by sources will contribute to the flux of UHECRs for E > E GZK K. Kotera and A. V. Olinto, ARA&A (2012) ev ev source discrimination well, there are EG/G magnetic fields and n δ... 11

12 UHECRs energy spectrum calculation Ingredients: source composition source spectral index maximum energy (E max ) cosmological evolution of the source luminosity χ loss depends on the energy and density of photon backgrounds. K. Kotera et al., JCAP (2010) Then: adjust spectral index on UHECRs data normalize the flux of UHECRs using a measured UHECRs spectrum use available constrains on secondary neutrinos and photons fluxes (Fermi-LAT, Ice-Cube and Auger) 12

13 Peculiar case: pure proton composition D. Allard, A&A (2007) Ankle can be fitted by the extragalactic component: ankle = e - e + dip (developed by Berezinsky et al.) 13

14 Mixed composition following low-energy galactic CRs abundances; rigidity dependent E max D. Allard, A&A (2007) small admixture of nuclei erases the dip ankle = transition G/EG (D. Allard et al.) composition getting lighter above ev Auger results cannot easily be understood as being due to propagation 14

15 A possible solution: Low E max models sources are not able to accelerate protons above few EeV but can accelerate nuclei of charge Z up to energies Z times higher (can be expected for astrophysical acceleration machanisms) E max = Z 4 EeV requires hard spectrum index relatively good description of the evolution of the composition 15

16 Comments on previous model Assumption: standard candles: same luminosity, same composition, same E max and cut-off above E max the value of the parameters depends on these assumptions they are effective parameters they would change by including for instance luminosity functions and E max dependence with luminosity Auger composition results could tell us that powerful UHE proton accelerators are rare in the local Universe but does not mean that these ev sources do not exist. L RC (10 18 ev) to be compared with L γ (MeV) Hillas plot 16

17 Hillas diagram: r L (E max ) < r s Simple selection criterium: sources must be capable of confining particles up to E max neutron star proton ev white dwarf Fe ev AGN AGN jets GRB hot spots SNR IGM shocks necessary condition but not sufficient! t acc < t esc + t age + t loss 17

18 How to spot UHE proton sources Within the CR horizon: large statistics anisotropy measurements. In particular, small scale clusters of events would certainly sign the presence of UHE proton sources Auger and TA continue to accumulate statistics (South and North) JEM-EUSO is particularly suitable for this task (both hemispheres) composition analysis: detection of deep showers observation of cosmic rays above ev (quasi for sure protons) Out of the CR horizon: multi-messenger astronomy diffuse cosmogenic neutrino flux point source of neutrinos most likely slightly extended for gamma-rays 18

19 Ongoing work end-to-end simulation to help reaching a global description of the phenomenon at ultrahigh energies Sources from 2MRS: density, angular distribution, luminosity model: mixed, mixedlow E max, Pure Iron extragalactic propagation: photon backgrounds, EGMF galactic propagation: GMF 19

20 2MRS We use 2MASS Redshift Survey to obtain the distribution of local matter The catalog is then corrected for peculiar velocities using EDD (available at Luminosity function We populate the Galactic Plane with a simple procedure to reflect that observed above and below 20

21 Selection of a volume-limited sample A magnitude-limited survey will be affected by radial-selection effects inability of the survey to detect fainter galaxies at large redshifts volume-limited sample: a maximum redshift and minimum absolute magnitude are chosen so that every galaxy in this redshift and magnitude range will be observed density of the seed sample: Mpc -3 galaxies are then drawn isotropically up to 1 Gpc according to the luminosity function 21

22 Extragalactic propagation from the sources to the Milky-Way Interactions with the ambient radiation fields. We talked about it... Propagation in EGMF EGMF are poorly known (spatial distribution, intensity, λ c, time evolution,...) expected to be very weak in the inter-cluster voids (B G) simplified approach: consider a purely turbulent, homogeneous MF following Giacalone & Jokipii (1999) for the modeling spatial transport by integrating the Lorentz equation protons in a B rms = 10 ng, λ c = 200 kpc 22

23 Example: pure Fe composition energy spectrum propagated energy spectrum of the 24 Z 26 component as a function of deflexion angle contribution of different intervals of source distances to the overall EGCR spectrum 23

24 Galactic propagation No interactions in the Galaxy (only few tens of kpc scale) Propagation in GMF. Ubiquitous in the Galaxy yet poorly understood large-scale regular component + a small-scale random part: both μg best constraints from Faraday rotation measures and polarized synchroton radiation Model from Jansson & Farrar (2012) disk field extended halo field out-of-plane component turbulent component whose intensity scales with the regular one 20 Strength of the regular magnetic field (µg) at z = 1000 pc 4 20 Strength of the regular magnetic field (µg) at z = 10 pc y [kpc] 0 0 regular component y [kpc] x [kpc] x [kpc] 4 24

25 Trajectories of EeV protons in the GMF For 30 energies in log(e/[ev]) = [17.5,20.5], we back-propagate millions of protons arrival direction on Earth - direction at the entrance of the Galaxy Identical trajectories for nuclei with same rigidity (E/Z) 25

26 5.01 EeV proton Regular: Jansson et al. Striated: = 1.4, c = 100 pc Turbulent: Scaling = 3, c = 100 pc map and histogram of deflexion angle 5 EeV protons = 130 EeV Fe nuclei Count cos

27 Some outcomes of the simulation Auger directional detection probability We produce lists of events at Earth taking into account the exposure of Auger and the future JEM-EUSO JEM-EUSO acceptance 27

28 Mixed composition Baseline sample: n δ = correlation with VCV a la Auger VCV is a tracer of the local matter mixed composition - proton dominated in agreement with Auger (2009) 2pt-correlation function in agreement with isotropic simulations for Auger JEM-EUSO! Large small-scale cluster of events expected. Proton astronomy disagreement with composition results from Auger 28

29 It would be cool source: 4 events and > 1% of the total number of events JEM-EUSO: N(>100 EeV) = 258 Auger: N(>55 EeV) = 69 29

30 Lower density: n δ = Mpc -3, completely ruled out? Should have been observed by Auger? JEM-EUSO: N(>80 EeV) =

31 Pure Fe composition n δ = 10-4 Mpc -3 JEM-EUSO: N(>80 EeV) = 574 Pure Fe composition would not fit well the Auger composition results 31

32 Mixed composition with low E max n δ = 10-5 Mpc -3 consistent with Auger anisotropy results reproduce the X max trend 32

33 Summary Auger confirmed the presence of spectral features and brought an unexpected composition evolution (that could also be evidence for exiting hadronic physics) The evolution of the composition can be understood if nuclei are accelerated at higher energies than protons in most sources Additional constraints can be brought by anisotropy measurements but Auger results are not yet totally compelling JEM-EUSO should help providing high statistics sky maps at UHE Is there really a difference between northern and southern sky? more statistics from TA and Auger needed to further constrain the presence of protons at UHE UHE proton source outside the cosmic-ray horizon could be revealed by multi-messenger observations