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A Method of Searching for Origins of Cosmic Rays correcting for - - PowerPoint PPT Presentation

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A Method of Searching for Origins of Cosmic Rays correcting for Galactic Field Deflections and Charge Composition Martin Erdmann, Gero Mller, Martin Urban , Marcus Wirtz martin.urban@rwth-aachen.de Current status Source Searches The Pierre

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martin.urban@rwth-aachen.de

A Method of Searching for Origins of Cosmic Rays correcting for Galactic Field Deflections and Charge Composition

Martin Erdmann, Gero Müller, Martin Urban, Marcus Wirtz

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martin.urban@rwth-aachen.de

Current status

2 Source Searches Composition

The Pierre Auger Collaboration, 2015, ApJ, 804 The Pierre Auger Collaboration, 2015,POS(ICRC 2015) 420

Separate Analyses → Point source searches → Large scale anisotropy → Mass composition UHECRs

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Motivation

3 Source Searches UHECRs Composition Galactic magnetic field allows for unified analysis Galactic Magnetic Field Spectrometer

The Pierre Auger Collaboration, 2015,POS(ICRC 2015) 420 The Pierre Auger Collaboration, 2015, ApJ, 804

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Galactic Magnetic Field Correction

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10Ne at 50 EeV 5Be at 50 EeV 1H at 50 EeV

■ Magnetic field models tuned to Faraday rotation and synchrotron emission measurements ■ Cosmic rays with different rigidities R=E/Z arrive on Earth at different directions

  • Source directions can only be found at edge of galaxy
  • Magnetic field corrections depend on cosmic ray charges

■ Correction of deflections in magnetic field using a probabilistic approach

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Analysis Strategy

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Monte Carlo Simulation

Monte Carlo simulation

Energy spectrum with E-2.6 Signal fraction: fs = 15 % Most abundant charges: H, He, C, N, O Sources: M87, Cen A & Fornax A smearing: ઠ = 3° Rigidity R=E/Z needed for projection to edge of galaxy, but charge? → Assign equal probability for each charge to each cosmic ray 6

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Projection to the edge of the galaxy

Galactic magnetic field ■ Regular field by Jansson and Farrar ■ Lensing technique

(H.-P. Bretz et al., 2014, Astropart.Phys. 54 110–117)

  • Probability to observe cosmic rays
  • riginating from (φ,θ) at the Galaxy

at direction (φ’,θ’) on Earth

  • Rigidity dependent

■ Transposed lens to project to edge

  • f galaxy

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Cluster identification

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Superimposed maps (rigidities) 1000 isotropic simulations

→ accept only directions exceeding 90% quantile probability of orign [A.U]

probability in pixel [A.U]

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Clusters and expected arrival directions

■

Search for directions with high arrival probability

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DBSCAN algorithmus (Ester, M. et al. (1996) KDD-96)

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Use cluster centers as source candidates

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Calculate expected arrival directions

  • n Earth using GMF

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Standard point source search with likelihood ratio

< 90 %

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Likelihood analysis

anticipated signal fraction smearing to account for random fields signal distribution background distribution cosmic ray direction

  • n Earth

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Model: Isotropy scenario excluded 10

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Charge determination

Update charge probabilities using projected source directions

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Cosmic Ray E=80 EeV → C = E / R = 8

Zfit: most probable charge ■ Charge resolution of ± 2.31

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Repeat analysis with updated rigidity distributions ■ Sources directions

  • improved directional reconstruction
  • Additional (unwanted) source candidate

■ Improved charge resolution ± 1.65

Iterative Procedure

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Conclusion and Outlook

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■ Method to identify source candidates by charge dependent corrections for deflections in GMF

  • Search for extragalactic directions
  • Evaluation of validity by likelihood ratio method
  • Cosmic ray charge resolution ≈ ± 2

■ Comparison of different magnetic field models ■ Inclusion of uncertainties, i.e. energy, direction ■ Application to data

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Backup

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Magnetic Field Lenses

■ Backtracking anti-protons from Earth to edge of galaxy

  • Using HEALPix scheme with nside=64
  • 175 rigidity bins between 1017.00 eV and 1020.49 eV with bin width log10(R/V)=0.02

■ Matrices projecting a probability distribution from edge of galaxy on Earth ■ Transposed lens answers question how probable cosmic rays at direction (φ, θ) on earth originate from direction (φ’, θ’) at edge of galaxy

15 pixel on Earth pixel at galaxy

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Lens Examples for log10R = 18.7 and log10R=19.7

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Galactic Magnetic Field - Cosmic Ray Flux

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Galactic Magnetic Field: Mean Deflections

18 JF12 PT11

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Galactic Magnetic Fields: Deflection Variances

19 JF12 PT11

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Results for 5 % signal fraction

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