The cosmic-ray electron spectrum measured with H.E.S.S. D. Kerszberg, M. Kraus, D. Kolitzus, K. Egberts, S. Funk, J.-P. Lenain, O. Reimer & P. Vincent for the H.E.S.S. Collaboration
The H.E.S.S. experiment H.E.S.S. phase I H.E.S.S. phase II 4 telescopes since 2003 5th telescope in 2012 960 PMT/camera 2048 PMT Field of view: 5° Field of view: 3.5° Stereoscopic reconstruction Designed for γ -ray detection. Daniel Kerszberg . The cosmic-ray electron spectrum measured with H.E.S.S. - ICRC 2017 - 19 July 2017 . 2/16
Cosmic-ray electron spectrum measurements status ] -1 sr 2 10 ⋅ -1 s ⋅ -2 m ⋅ 2 [GeV HESS HE (2008) HESS LE (2009) dN dE MAGIC (2011) 3 Flux E AMS-02 (2014) 10 VERITAS (2015) Fermi-LAT LE (2017) Fermi-LAT HE (2017) -3 -2 -1 10 10 10 1 10 Energy [TeV] 2008/2009 H.E.S.S. results with multivariate analysis. In 2017: up to 14 years of observations with H.E.S.S. –> Standard analysis relying on cut on very discriminating variable. F . Aharonian et al. , A&A 508 (2009), 561 F . Aharonian et al. , Phys. Rev. Lett. 101 (2008), 261104 Daniel Kerszberg . The cosmic-ray electron spectrum measured with H.E.S.S. - ICRC 2017 - 19 July 2017 . 3/16
Standard analysis method The Model Analysis : 0.12 Log-likelihood comparison MC electrons Normalized distribtution [arbitrary units] between recorded images and 0.1 MC protons pre-calculated templates Cut position 0.08 including Night Sky Background 0.06 Widely used for H.E.S.S. 0.04 analysis 0.02 Very powerful discrimination based on goodness of fit 0 -4 -2 0 2 4 6 8 10 Discriminating variable M. de Naurois & L. Rolland, Astropart. Phys., 32 (2009), 231-252 Daniel Kerszberg . The cosmic-ray electron spectrum measured with H.E.S.S. - ICRC 2017 - 19 July 2017 . 4/16
Dataset for the electron analysis In addition to the standard data quality selection, we used the following criteria: Pointing position is more than 7 degrees away from the Galactic plane H.E.S.S. I runs with 4 telescopes operational Zenith angle is < 28° Excluded regions: 0.4°around any known γ -ray source. Final dataset consists in 2742 runs for a total livetime of ∼ 1186 hours . Daniel Kerszberg . The cosmic-ray electron spectrum measured with H.E.S.S. - ICRC 2017 - 19 July 2017 . 5/16
Estimated background contamination Preliminary estimation of proton contamination with MC simulations (knowing the actual measured fluxes of electrons and protons): Energy Expected contamination from protons ∼ 15 % 1 TeV ∼ 7 % 2 TeV < 10 % > 5 TeV Energy range of the analysis : [0.25 TeV; 25 TeV] Total number of electron-like detected events : 480 739 Daniel Kerszberg . The cosmic-ray electron spectrum measured with H.E.S.S. - ICRC 2017 - 19 July 2017 . 6/16
New H.E.S.S. cosmic-ray electron spectrum ] -1 sr 2 10 ⋅ -1 s ⋅ -2 m ⋅ 2 [GeV HESS HE (2008) HESS LE (2009) dN dE MAGIC (2011) AMS-02 (2014) 3 Flux E VERITAS (2015) 10 Fermi-LAT LE (2017) Fermi-LAT HE (2017) HESS (2017) Preliminary -3 -2 -1 10 10 10 1 10 Energy [TeV] Daniel Kerszberg . The cosmic-ray electron spectrum measured with H.E.S.S. - ICRC 2017 - 19 July 2017 . 7/16
Background issue Contamination from protons is the main issue for an electron analysis! Because electron spectrum is steeper than proton spectrum, protons induce an hardening in the electron spectrum even if only a small number is mis- identified as electrons. Daniel Kerszberg . The cosmic-ray electron spectrum measured with H.E.S.S. - ICRC 2017 - 19 July 2017 . 8/16
Background issue 8 10 Range of fit : [0.5 TeV - 6 TeV] ± Fitted index = -2.75 0.14 Contamination from protons is [arbitrary units] the main issue for an electron 7 10 analysis! dN dE Because electron spectrum is 3 6 Flux E 10 steeper than proton spectrum, protons induce an hardening in the electron spectrum even Preliminary if only a small number is mis- 1 10 identified as electrons. True Energy [TeV] Injection of MC protons with simulated spectral index of -2.8 reconstructed using protons acceptance. Daniel Kerszberg . The cosmic-ray electron spectrum measured with H.E.S.S. - ICRC 2017 - 19 July 2017 . 9/16
Background issue 8 10 Range of fit : [1 TeV - 10 TeV] ± Fitted index = -2.20 0.33 Contamination from protons is [arbitrary units] the main issue for an electron 7 10 analysis! dN dE Because electron spectrum is 3 6 Flux E 10 steeper than proton spectrum, protons induce an hardening in the electron spectrum even Preliminary if only a small number is mis- 1 10 identified as electrons. True Energy [TeV] Injection of MC protons with simulated spectral index of -2.8 reconstructed using electrons acceptance. Daniel Kerszberg . The cosmic-ray electron spectrum measured with H.E.S.S. - ICRC 2017 - 19 July 2017 . 10/16
Fitting of the spectrum Fit function is a smooth broken power law: ] -1 sr Preliminary ⋅ -1 s ⋅ -2 m � − (Γ 1 − Γ 2 ) α 2 � 10 � 1 ⋅ 2 3 − Γ 1 � [GeV d E = N 0 ( ( 1 TeV ) ) E 3 d N E E α 1 + Eb dN dE 3 Flux E Result of the fit: 10 HESS HE (2008) HESS LE (2009) Γ 1 = 3 . 04 ± 0 . 01 (stat) MAGIC (2011) AMS-02 (2014) Γ 2 = 3 . 78 ± 0 . 02 (stat) E b = 0 . 94 ± 0 . 02 (stat) TeV VERITAS (2015) Fermi-LAT HE (2017) N 0 = 105 ± 1 (stat) GeV 2 · m − 2 · sr − 1 · s − 1 HESS (2017) HESS Fit (2017) α = 0 . 12 ± 0 . 01 (stat) 1 1 10 Energy [TeV] Daniel Kerszberg . The cosmic-ray electron spectrum measured with H.E.S.S. - ICRC 2017 - 19 July 2017 . 11/16
Systematics uncertanties The systematics studies included: Test on all event selection cuts involved in the analysis Dependency on the zenithal angle Dependency over the years Dependency on atmospheric conditions Total systematic errors: quadratic sum of each tests. + 0 . 10 Γ 1 = 3 . 04 ± 0 . 01 (stat) − 0 . 18 (sys) + 0 . 17 Γ 2 = 3 . 78 ± 0 . 02 (stat) − 0 . 06 (sys) + 0 . 29 E b = 0 . 94 ± 0 . 02 (stat) − 0 . 26 (sys) TeV + 27 (sys) GeV 2 · m − 2 · sr − 1 · s − 1 N 0 = 104 ± 1 (stat) − 16 + 0 . 19 α = 0 . 12 ± 0 . 01 (stat) − 0 . 05 (sys) Daniel Kerszberg . The cosmic-ray electron spectrum measured with H.E.S.S. - ICRC 2017 - 19 July 2017 . 12/16
Electron spectrum with systematic uncertanties Preliminary 2 10 ] -1 sr ⋅ -1 s ⋅ -2 m HESS HE (2008) ⋅ 2 [GeV HESS LE (2009) MAGIC (2011) dN 10 dE AMS-02 (2014) 3 VERITAS (2015) Flux E Fermi-LAT HE (2017) HESS (2017) HESS Fit (2017) Stat. + sys. errors 1 1 10 Energy [TeV] Daniel Kerszberg . The cosmic-ray electron spectrum measured with H.E.S.S. - ICRC 2017 - 19 July 2017 . 13/16
Featureless spectrum up to the highest energies HESS HE (2008) HESS LE (2009) MAGIC (2011) AMS-02 (2014) VERITAS (2015) Fermi-LAT HE (2017) ] -1 sr HESS (2017) T. Kobayashi et al. (2004) ⋅ -1 s Stat. + sys. errors HESS Fit (2017) ⋅ -2 m ⋅ 2 2 10 [GeV Vela dN dE 3 Flux E Preliminary Cygnus Loop 1 10 Energy [TeV] T. Kobayashi et al. , ApJ, 601:340-351 (2004) Daniel Kerszberg . The cosmic-ray electron spectrum measured with H.E.S.S. - ICRC 2017 - 19 July 2017 . 14/16
Summary Electron spectrum measured with standard analysis allowing excellent background rejection. Detection of 480 739 electron-like events from 250 GeV up to ∼ 20 TeV. Electron spectrum fitted with a smooth broken power law: low energy index Γ 1 = 3 . 04 ± 0 . 01 (stat) + 0 . 10 − 0 . 18 (sys) high energy index Γ 2 = 3 . 78 ± 0 . 02 (stat) + 0 . 17 − 0 . 06 (sys) break at E b = 0 . 94 ± 0 . 02 (stat) + 0 . 29 − 0 . 26 (sys) TeV flux at 1 TeV Φ( 1 TeV ) = 96 ± 1 (stat) ± 17 (sys) GeV 2 .m − 2 .sr − 1 .s − 1 No features is seen in the electron spectrum up to the highest energies which allow us to exclude models that describe prominent features from nearby sources such as Vela. Please refer to the forthcoming paper from the H.E.S.S. Collaboration! Daniel Kerszberg . The cosmic-ray electron spectrum measured with H.E.S.S. - ICRC 2017 - 19 July 2017 . 15/16
] -1 sr 2 10 ⋅ -1 s ⋅ -2 m ⋅ 2 [GeV HESS HE (2008) HESS LE (2009) MAGIC (2011) dN dE AMS-02 (2014) 3 Flux E VERITAS (2015) Fermi-LAT LE (2017) 10 Fermi-LAT HE (2017) HESS (2017) Preliminary Stat. + sys. errors -3 -2 -1 10 10 10 1 10 Energy [TeV] Thank you for your attention! Daniel Kerszberg . The cosmic-ray electron spectrum measured with H.E.S.S. - ICRC 2017 - 19 July 2017 . 16/16
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