cosmic ray electrons and gc observations with h.e.s.s. · 2009. 7. 20. · cosmic ray electrons...
TRANSCRIPT
-
Cosmic Ray Electronsand GC Observations with H.E.S.S.
Christopher van Eldik (for the H.E.S.S. Collaboration)MPI für Kernphysik, Heidelberg, Germany
TeVPA '09, SLAC, July 2009
-
The Centre of the Milky Way
C. van Eldik • TeV PA 2009
-
Aharonian et al. (2006)
H.E.S.S. 2004 (55 hours)
G 0.9+0.1
H.E.S.S. J1745-29038 sigma (55h)H.E.S.S. J1745-290point-like < 1.2' (95% CL)
The Centre of the Milky Way
C. van Eldik • TeV PA 2009
-
Diffuse emission
H.E.S.S. 2004 (55 hours)
G 0.9+0.1H.E.S.S. J1745-290point-like < 1.2' (95% CL)
The Centre of the Milky Way
Aharonian et al. (2006)
C. van Eldik • TeV PA 2009
-
● Lack of γ-raysfor l > 1°
● Injection ofprotons at GC
● Assumek = ~3 kpc2 Myr-1for TeV protons→ injection 104 years ago
● Fits age ofSgr A East
Molecular Cloud Association
C. van Eldik • TeV PA 2009
-
● Not just passive illumination- enhanced flux for > 1 TeV- photon index ~2.3
● Similar index as HESS 1745-290everywhere in the region
C. van Eldik • TeV PA 2009
Diffuse Emission Spectrum
-
VLA Chandra
SNR Sgr A East? SMBH Sgr A*? DM? PWN G359.95-0.04?
10''300''
Possible Counterparts?
C. van Eldik • TeV PA 2009
-
VLA Chandra
SNR Sgr A East? SMBH Sgr A*? DM? PWN G359.95-0.04?
10''300''
Possible Counterparts?
C. van Eldik • TeV PA 2009
● Position?● Variability?● Energy spectrum?
-
Sgr A*Sgr A East
Best Fit HESS J1745-290 (Aharonian et al. 2004)Best Fit HESS J1745-290 (van Eldik et al. 2007) - preliminary-
VLA 90cm image
0.04 deg
Position: Sgr A East ruled out
CvE et al., Proc. ICRC (2007)
● Dedicated data set using optical guiding telescopes
● 6'' systematic pointing error
● Lack of association with Sgr A East
● Chance probability 10-4 ... 10-11
C. van Eldik • TeV PA 2009
-
Variability studies● Sgr A* highly variable at other wavelengths● Quasi-periodic oscillation● Expect correlated VHE variability if emission produced close to BH surface● No obvious variability in VHE lighcurve observed based on 93 hours of data
Aharonian et al. (2009), arXiv:0906.1247
HESS J1745-290, 28 min flux points
C. van Eldik • TeV PA 2009
-
Flare Sensitivity
Aharonian et al. (2009)
● Maximum needed lightcurve “amplification” for 3σ flare detection● (as usual) statistics limited
Ahar
onia
n et
al.
(200
9)
C. van Eldik • TeV PA 2009
-
Variability studies● Simultaneous HESS and
Chandra observations
● X-ray flare detected- 1700s duration- 9x quiescent level
● No increase of gamma flux→ 100% flux increase discarded at 99% CL
Aharonian et al. (2008)
C. van Eldik • TeV PA 2009
-
Search for QPOs (small time scales)● Quasi-periodic oscillations observed in X-rays and IR● X-ray periodicity 100 s, 219 s, 700 s, 1150 s, 2250 s● Related to accretion disk?● Rayleigh test for continuous 28 min observations (2004-2006 averaged)
→ no hint for QPOs < 1150 s in VHE data
Ahar
onia
n et
al.
(200
9)
C. van Eldik • TeV PA 2009
-
Search for QPOs (large time scales)● Lomb-Scargle periodogram
averaged over 2004-2006● Power spectrum compatible
with noise● No indication for QPOs
on 600 s – 1.5 h time scales
Ahar
onia
n et
al.
(200
9)
C. van Eldik • TeV PA 2009
-
C. van Eldik • TeV PA 2009
Spectrum – a bit of history
● Hard spectrum: Γ = 2.25 ± 0.04 ± 0.10● 10% Crab above 1 TeV● No cut-off: EC > 9 TeV (95% CL)
-
● 2004-2006 data93 h live time
● 4185 γ-rays (61 σ)160 GeV < E < 70 TeV
● Exponential cut-offΓ = 2.10±0.04±0.10Ec = 15.7±3.5±2.5 TeVχ²/d.o.f. = 23/26
Aharonian et al. (2009)A&A acceptedarXiv:0906.1247
HESS J1745-290Spectrum
C. van Eldik • TeV PA 2009
-
Aharonian et al. (2009)A&A acceptedarXiv:0906.1247
HESS J1745-290Spectrum
C. van Eldik • TeV PA 2009
● 2004-2006 data93 h live time
● 4185 γ-rays (61 σ)160 GeV < E < 70 TeV
● Exponential cut-offΓ = 2.10±0.04±0.10Ec = 15.7±3.5±2.5 TeVχ²/d.o.f. = 23/26
● Broken powerlawΓ1 = 2.02±0.08±0.10Γ2 = 2.63±0.14±0.10EB = 2.57±0.19±0.44χ²/d.o.f. = 20/19
-
10''
Sgr A*
G359.95
Wang et al. (2005)
Hinton + Aharonian (2007)
● Dense radiation fields● Comparably low
magnetic field→ IC dominant→ plausible candidate
C. van Eldik • TeV PA 2009
HESS J1745: a pulsar wind nebula?
-
● All models viablewith current statistics
● CTA/AGIS will help● LAT?
Sgr A* Emission Modelspp interactionsin accretion disk
Aharonian & Neronov (2005)
electron scenariocurvature + IC
-
Cosmic Ray Electrons
Aharonian et al. (2008)
● Suffer severely from synchrotron and inverse Compton losses → steep GeV spectrum ~E-3.3 → steepening at TeV energies ~E-3.9 → TeV electrons must come from local sources
● Compatible with lower-energy measurements: Г = 3.1 with cut-off at 2.1 TeV
● H.E.S.S. can measure electrons at TeV energies → electrons are gamma-like → large detection area
● Large backgrounds - Cosmic ray showers - Galactic diffuse emission - extragalactic diffuse emission
-
Standard Background Modelling
Ber
ge e
t al.
(200
7)
C. van Eldik • TeV PA 2009
-
● Random Forest: train machine learning algorithm on shower image parameters → needs electron simulations and cosmic background for training
● For each shower, RF determines “electron likeness” parameter ζ ε [0;1]
● For ζ>0.9, total background suppression is 10-6
● Signal extraction → Fit ζ-distribution with combination of electron/proton simulations → depends on hadronic interaction model (Sybill/QGSJet)
data
simulatedbackground
Electrons: Background Modelling
C. van Eldik • TeV PA 2009
-
● Extrapolation of gamma-ray flux to VHE energies suggests small contribution only
● FERMI preliminary extragalactic diffuse gamma flux softer than EGRET
● Test with first interaction height (only poorly reconstructed)
● At most 50% gamma contamination
Gamma-ray contamination
Aharonian et al. (2008)
C. van Eldik • TeV PA 2009
-
● Separate fits in energy bands
● Two complementary analyses: - high energies: 600 GeV – 5 TeV (hard cuts for best reconstruction) - low energies: 340 GeV – 700 GeV (looser cuts on image intensity, 2004/2005 data only)
Energy Spectrum
Aharonian et al. (2008)
Aharonian et al. (2009) arXiv:0905.0105
C. van Eldik • TeV PA 2009
-
● No indication of feature similar to ATIC
● Break in spectrum: Г1 = 3.0±0.1±0.3 Г2 = 4.1±0.3±0.3 EB = 0.9±0.1 TeV
● Compatible to FERMI within energy shift uncertainty
Aharonian et al. 2009
C. van Eldik • TeV PA 2009
Low Energy Analysis
Aharonian et al. (2009) arXiv:0905.0105
-
Meade et al. (2009)arXiv:0905.0480
Putting Electrons and GC together
-
Summary● Solid detection of the GC point source● Sgr A East excluded as a source● After 100 hours of observation, spectrum shows significant deviation simple power-law● No indication for variability● No indication for QPOs
● Measurement of CR electrons (+ extragalactic diffuse gammas)● Implies existence of nearby sources● Energy range 340 GeV – 5 TeV● Consistent with FERMI● No indication for ATIC spectral feature● Significant spectral steepening beyond 1 TeV
Thanks!
Slide 1Slide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Slide 27