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The cosmic-ray electron spectrum measured with H.E.S.S. D. - - PowerPoint PPT Presentation

Apr 06, 2023 542 likes •715 views

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

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SLIDE 1

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

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SLIDE 2

The H.E.S.S. experiment

H.E.S.S. phase I 4 telescopes since 2003 960 PMT/camera Field of view: 5° Stereoscopic reconstruction H.E.S.S. phase II 5th telescope in 2012 2048 PMT Field of view: 3.5° 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

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SLIDE 3

Cosmic-ray electron spectrum measurements status

Energy [TeV]

  • 3

10

  • 2

10

  • 1

10 1 10 ]

  • 1

sr ⋅

  • 1

s ⋅

  • 2

m ⋅

2

[GeV dE dN

3

Flux E 10

2

10

HESS HE (2008) HESS LE (2009) MAGIC (2011) AMS-02 (2014) VERITAS (2015) Fermi-LAT LE (2017) Fermi-LAT HE (2017)

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

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SLIDE 4

Standard analysis method

The Model Analysis: Log-likelihood comparison between recorded images and pre-calculated templates including Night Sky Background Widely used for H.E.S.S. analysis Very powerful discrimination based on goodness of fit

Discriminating variable

  • 4
  • 2

2 4 6 8 10 Normalized distribtution [arbitrary units]

0.02 0.04 0.06 0.08 0.1 0.12

MC electrons MC protons Cut position

  • 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

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SLIDE 5

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

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SLIDE 6

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 1 TeV

∼ 15%

2 TeV

∼ 7% > 5 TeV < 10%

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

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SLIDE 7

New H.E.S.S. cosmic-ray electron spectrum

Energy [TeV]

  • 3

10

  • 2

10

  • 1

10 1 10 ]

  • 1

sr ⋅

  • 1

s ⋅

  • 2

m ⋅

2

[GeV dE dN

3

Flux E 10

2

10

HESS HE (2008) HESS LE (2009) MAGIC (2011) AMS-02 (2014) VERITAS (2015) Fermi-LAT LE (2017) Fermi-LAT HE (2017) HESS (2017)

Preliminary

Daniel Kerszberg . The cosmic-ray electron spectrum measured with H.E.S.S. - ICRC 2017 - 19 July 2017 . 7/16

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SLIDE 8

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

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SLIDE 9

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.

True Energy [TeV] 1 10 [arbitrary units] dE dN

3

Flux E

6

10

7

10

8

10

Range of fit : [0.5 TeV - 6 TeV] 0.14 ± Fitted index = -2.75

Preliminary

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

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SLIDE 10

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.

True Energy [TeV] 1 10 [arbitrary units] dE dN

3

Flux E

6

10

7

10

8

10

Range of fit : [1 TeV - 10 TeV] 0.33 ± Fitted index = -2.20

Preliminary

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

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SLIDE 11

Fitting of the spectrum

Fit function is a smooth broken power law:

E3 dN

dE = N0( E (1 TeV)) 3−Γ1

  • 1+
  • E

Eb

1

α

−(Γ1−Γ2)α

Result of the fit:

Γ1 = 3.04 ± 0.01 (stat) Γ2 = 3.78 ± 0.02 (stat)

Eb = 0.94 ± 0.02 (stat) TeV N0 = 105 ± 1 (stat) GeV2·m−2·sr−1·s−1

α = 0.12 ± 0.01 (stat)

Energy [TeV] 1 10 ]

  • 1

sr ⋅

  • 1

s ⋅

  • 2

m ⋅

2

[GeV dE dN

3

Flux E 1 10

2

10

HESS HE (2008) HESS LE (2009) MAGIC (2011) AMS-02 (2014) VERITAS (2015) Fermi-LAT HE (2017) HESS (2017) HESS Fit (2017)

Preliminary

Daniel Kerszberg . The cosmic-ray electron spectrum measured with H.E.S.S. - ICRC 2017 - 19 July 2017 . 11/16

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SLIDE 12

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.

Γ1 = 3.04 ± 0.01 (stat)

+0.10 −0.18 (sys)

Γ2 = 3.78 ± 0.02 (stat)

+0.17 −0.06 (sys)

Eb = 0.94 ± 0.02 (stat)

+0.29 −0.26 (sys) TeV

N0 = 104 ± 1 (stat)

+27 −16

(sys) GeV2·m−2·sr−1·s−1

α = 0.12 ± 0.01 (stat)

+0.19 −0.05 (sys)

Daniel Kerszberg . The cosmic-ray electron spectrum measured with H.E.S.S. - ICRC 2017 - 19 July 2017 . 12/16

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SLIDE 13

Electron spectrum with systematic uncertanties

Energy [TeV] 1 10 ]

  • 1

sr ⋅

  • 1

s ⋅

  • 2

m ⋅

2

[GeV dE dN

3

Flux E 1 10

2

10

HESS HE (2008) HESS LE (2009) MAGIC (2011) AMS-02 (2014) VERITAS (2015) Fermi-LAT HE (2017) HESS (2017) HESS Fit (2017)

  • Stat. + sys. errors

Preliminary

Daniel Kerszberg . The cosmic-ray electron spectrum measured with H.E.S.S. - ICRC 2017 - 19 July 2017 . 13/16

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SLIDE 14

Featureless spectrum up to the highest energies

Energy [TeV] 1 10 ]

  • 1

sr ⋅

  • 1

s ⋅

  • 2

m ⋅

2

[GeV dE dN

3

Flux E

2

10

HESS HE (2008) HESS LE (2009) MAGIC (2011) AMS-02 (2014) VERITAS (2015) Fermi-LAT HE (2017) HESS (2017) (2004) et al.

  • T. Kobayashi
  • Stat. + sys. errors

HESS Fit (2017)

Vela Cygnus Loop Preliminary

  • 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

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SLIDE 15

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 Γ1 = 3.04 ± 0.01 (stat) +0.10

−0.18 (sys)

high energy index Γ2 = 3.78 ± 0.02 (stat) +0.17

−0.06 (sys)

break at Eb = 0.94 ± 0.02 (stat) +0.29

−0.26 (sys) TeV

flux at 1 TeV Φ(1 TeV) = 96 ± 1 (stat) ±17 (sys) GeV2.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

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SLIDE 16

Energy [TeV]

  • 3

10

  • 2

10

  • 1

10 1 10 ]

  • 1

sr ⋅

  • 1

s ⋅

  • 2

m ⋅

2

[GeV dE dN

3

Flux E 10

2

10

HESS HE (2008) HESS LE (2009) MAGIC (2011) AMS-02 (2014) VERITAS (2015) Fermi-LAT LE (2017) Fermi-LAT HE (2017) HESS (2017)

  • Stat. + sys. errors

Preliminary

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