The cosmic-ray electronspectrum measured with H.E.S.S.D. Kerszberg, M. Kraus, D. Kolitzus, K. Egberts,S. Funk, J.-P. Lenain, O. Reimer & P. Vincentfor the H.E.S.S. Collaboration

The H.E.S.S. experiment

H.E.S.S. phase I4 telescopes since 2003960 PMT/cameraField of view: 5°Stereoscopic reconstruction

H.E.S.S. phase II5th telescope in 20122048 PMTField 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

Cosmic-ray electron spectrum measurements status

Energy [TeV]

-310 -210 -110 1 10

]-1

sr⋅-1 s⋅

-2m⋅2

[G

eVd

Ed

N 3

Flu

x E

10

210

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), 561F. 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:

Log-likelihood comparisonbetween recorded images andpre-calculated templatesincluding Night SkyBackground

Widely used for H.E.S.S.analysis

Very powerful discriminationbased on goodness of fit

Discriminating variable-4 -2 0 2 4 6 8 10

No

rmal

ized

dis

trib

tuti

on

[ar

bit

rary

un

its]

0

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

Dataset for the electron analysis

In addition to the standard data quality selection, we used the followingcriteria:

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

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

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

Energy [TeV]

-310 -210 -110 1 10

]-1

sr⋅-1 s⋅

-2m⋅2

[G

eVd

Ed

N 3

Flu

x E

10

210

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

Background issue

Contamination from protons isthe main issue for an electronanalysis!

Because electron spectrum issteeper than proton spectrum,protons induce an hardeningin the electron spectrum evenif 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

Contamination from protons isthe main issue for an electronanalysis!

Because electron spectrum issteeper than proton spectrum,protons induce an hardeningin the electron spectrum evenif only a small number is mis-identified as electrons. True Energy [TeV]

1 10 [

arb

itra

ry u

nit

s]d

Ed

N 3

Flu

x E 610

710

810Range of fit : [0.5 TeV - 6 TeV]

0.14±Fitted index = -2.75

Preliminary

Injection of MC protons with simulatedspectral index of -2.8 reconstructed usingprotons acceptance.

Daniel Kerszberg . The cosmic-ray electron spectrum measured with H.E.S.S. - ICRC 2017 - 19 July 2017 . 9/16

Background issue

Contamination from protons isthe main issue for an electronanalysis!

Because electron spectrum issteeper than proton spectrum,protons induce an hardeningin the electron spectrum evenif only a small number is mis-identified as electrons. True Energy [TeV]

1 10 [

arb

itra

ry u

nit

s]d

Ed

N 3

Flu

x E 610

710

810Range of fit : [1 TeV - 10 TeV]

0.33±Fitted index = -2.20

Preliminary

Injection of MC protons with simulatedspectral index of -2.8 reconstructed usingelectrons 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 brokenpower law:

E3 dNdE = N0( E

(1 TeV))3−Γ1

(1+(

EEb

) 1α

)−(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⋅

-2m⋅2

[G

eVd

Ed

N 3

Flu

x E

1

10

210

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

Systematics uncertanties

The systematics studies included:

Test on all event selection cuts involved in the analysisDependency on the zenithal angleDependency over the yearsDependency 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

Electron spectrum with systematic uncertanties

Energy [TeV]1 10

]-1

sr⋅-1 s⋅

-2m⋅2

[G

eVd

Ed

N 3

Flu

x E

1

10

210

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

Featureless spectrum up to the highest energies

Energy [TeV]1 10

]-1

sr⋅-1 s⋅

-2m⋅2

[G

eVd

Ed

N 3

Flu

x E

210

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 LoopPreliminary

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 excellentbackground 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 energieswhich allow us to exclude models that describe prominent features fromnearby 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

Energy [TeV]-310 -210 -110 1 10

]-1

sr⋅-1 s⋅

-2m⋅2

[G

eVd

Ed

N 3

Flu

x E

10

210

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. errorsPreliminary

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