the cosmic-ray electron spectrum measured with h.e.s.s. · 2017-07-19 · the cosmic-ray electron...
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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