Very high energy  -ray observations of the Galactic Center with H.E.S.S. Matthieu Vivier IRFU/SPP CEA-Saclay On behalf the H.E.S.S. collaboration

Outline  Context  The H.E.S.S. observations of the Galactic Center  Position & mophology of HESS J  Spectrum & variability  Models for TeV  -rays at the GC (if time)  Conclusions Battle plan Moriond 20092Matthieu Vivier

Context  MWL source in the central parsecs of our Galaxy: emitting from radio to TeV  - rays  From radio to X-rays: originates from the SMBH Sgr A*  Origin of the hard X-rays/Tev  -rays? Radio IR X-rays TeV Sgr A*? Moriond 20093Matthieu Vivier

Context  MWL source in the central parsecs of our Galaxy: emitting from radio to TeV  - rays  From radio to X-rays: originates from the SMBH Sgr A*  Origin of the hard X-rays/Tev  -rays? Possible counterparts: SNR Sgr A East, PWN G , Sgr A*… + G ≈ 10pc×10pc H.E.S.S. angular resolution Moriond 20094Matthieu Vivier

Context  Highly variable in radio, IR & X-rays Moriond 20095Matthieu Vivier

Context  Highly variable in radio, IR & X-rays →106 days periodic modulation in the radio flux: accretion disk? Moriond 20096Matthieu Vivier Fourier power spectrum: VLA data Zhao, Bower & Goss (2001)

Context  Highly variable in radio, IR & X-rays →106 days periodic modulation in the radio flux: accretion disk? →IR/X-ray flares of ≈ 1h time duration + QPOs: strongly supports the idea of an accretion disk around Sgr A* IR flare of June 16 th, 2003: VLT data Genzel et al. (2003) Fourier power spectrum: VLA data Zhao, Bower & Goss (2001) Moriond 20097Matthieu Vivier

The observations of the GC in 2004  Detection of a point-like source: power-law spectrum + non variable emission on timescales < 1 year Moriond 20098Matthieu Vivier

The observations of the GC in 2004  Detection of a point-like source: power-law spectrum + non variable emission on timescales < 1 year  Spectrum incompatible with DM particle annihilations: the fits are bad in the low & high energy parts. 14 TeV 5 TeV 10 TeV « HESS Observations of the Galactic Center Region and Their Possible Dark Matter Interpretation », PRL, 97 (2006) Moriond 20099Matthieu Vivier

The observations of the GC in 2004  Detection of a point-like source: power-law spectrum + non variable emission on timescales < 1 year  Spectrum incompatible with DM particle annihilations: the fits are bad in the low & high energy parts.  A DM contribution is not excluded: estimated to be < 10% 14 TeV 5 TeV 10 TeV « HESS Observations of the Galactic Center Region and Their Possible Dark Matter Interpretation », PRL, 97 (2006) Moriond Matthieu Vivier

The observations  dataset: 100h (≈ 0.1 year of data collection)  3 sources in the 5°×5° FoV:  GC source HESS J : point- like, 60  detection.  SNR G : point-like.  extended source 3EG J (EGRET). HESS J G EG J ~ 500 pc X 500 pc b (deg) l (deg) Moriond Matthieu Vivier

The observations  dataset: 100h (≈ 0.1 year of data collection)  3 sources in the 5°×5° FoV  Diffuse emission along the galactic plane « Discovery of very high energy  -rays from the Galactic Centre ridge », Nature 439 (2006) HESS J ~ 500 pc X 500 pc b (deg) l (deg) expected level of background events Moriond Matthieu Vivier

The observations  dataset: 100h (≈ 0.1 year of data collection)  3 sources in the 5°×5° FoV  Diffuse emission along the galactic plane « Discovery of very high energy  -rays from the Galactic Centre ridge », Nature 439 (2006)  statistic of ≈ 4000 events in a circular 0.1° region centered on the GC. HESS J ~ 500 pc X 500 pc b (deg) l (deg) expected level of background events ON source region Moriond Matthieu Vivier

The observations  dataset: 100h (≈ 0.1 year of data collection)  3 sources in the 5°×5° FoV  Diffuse emission along the galactic plane « Discovery of very high energy  -rays from the Galactic Centre ridge », Nature 439 (2006)  statistic of ≈ 4000 events in a circular 0.1° region centered on the GC. HESS J ~ 500 pc X 500 pc b (deg) l (deg) expected level of background events ON source region Position/morphology Spectrum/variability Moriond Matthieu Vivier

Position & morphology SNR SgrA East (90 cm) van Eldik et al., ICRC (2007)  point-like source: intrisic size < 1.2’ (≈ 2.9 pc) at the 99% C.L.  position: l=359°56’41.1’’± 6.4’’± 6’’ b=-0°2’39.2’’ ± 5.9’’ ±6’’  centroid emission located at 7’’ ± 12’’ from Sgr A*  Sgr A East excluded at the 7  C.L.  G still inside error bars (8.7’’ from Sgr A*) Moriond Matthieu Vivier

The spectrum broken power-law   = 2.02 ± 0.08  2 = 2.63 ± 0.14 E break = 2.57 ± 0.19 TeV power-law with an exponential cut-off  = 2.10 ± 0.04 E cut = 15.7 ± 3.40 TeV E cut power-law log(E) Flux E break power-law 11 22 log(E) Flux  curvature in the spectrum: deviates from a power-law in the high energy part. Moriond Matthieu Vivier

The spectrum broken power-law   = 2.02 ± 0.08  2 = 2.63 ± 0.14 E break = 2.57 ± 0.19 TeV power-law with an exponential cut-off  = 2.10 ± 0.04 E cut = 15.7 ± 3.40 TeV Fit residuals Moriond Matthieu Vivier  curvature in the spectrum: deviates from a power-law in the high energy part.

Variability  run-by-run light curve (integrated fluxes per 28 min intervals) compatible with a constant  flare sensitivity study:  2 /dof = 233/216 Moriond Matthieu Vivier

Variability  Is the TeV signal correlated with the X-ray signal? →simultaneous observations with the Chandra satellite in  Limit on the TeV flux increase during the flare: < factor 2 (99% C.L)  In agreement with the flare sensitivity study. J.Hinton, M.V, et al., (HESS) ICRC 2007 « Simultaneous H.E.S.S. and Chandra observations of Sgr A* during an X-ray flare », A&A 492L, 25 (2009) Moriond Matthieu Vivier

Variability  QPO structures in the IR & X-rays flares: likely to correspond to oscillation modes of an accretion disk around Sgr A* ( ♭ : oscillations not confirmed in IR by the Keck telescopes) Moriond Matthieu Vivier

Variability  QPO structures in the IR & X-rays flares: likely to correspond to oscillation modes of an accretion disk around Sgr A* ( ♭ : oscillations not confirmed in IR by the Keck telescopes)  2 cases: 1) The coherence time of the disk oscillations is short: Rayleigh test on photon time arrival distribution in a data run (< 28 min) + average of the Rayleigh power at one frequency over the whole runs 100 s 219 s 1150s 700s Rayleigh test  2 /dof = 35/29 M.V et al., ICRC (2007) Moriond Matthieu Vivier

Variability  QPO structures in the IR & X-rays flares: likely to correspond to oscillation modes of an accretion disk around Sgr A* ( ♭ : oscillations not confirmed in IR by the Keck telescopes)  2 cases: 2) The coherence time of the disk oscillations is of the order of a few hours: Lomb-Scargle periodogram on 5 min integrated fluxes in a night of data collection (≤ few hours) + average of the Fourier power at each tested frequency over the whole nights. Lomb-Scargle periodogram M.V et al., ICRC (2007) Moriond Matthieu Vivier

VHE emission models  Leptonic models: inverse Compton scattering of leptons on the dense photon fields (UV/Optical/IR) in the vicinity of Sgr A*. Origin of the leptons? →From the nearby pulsar G : Hinton & Aharonian (2007) →Stochastic acceleration of leptons in an accretion disk around Sgr A*: Liu et al. (2006), Atoyan & Dermer (2004)  cut-off caused by the Klein-Nishina effect. No expected variability. Hinton & Aharonian (2007) Black Hole Plerion model Atoyan & Dermer (2004) Moriond Matthieu Vivier

VHE emission models  Hadronic models: acceleration of protons in the vicinity of the supermassive black hole, Ballantyne et al. (2007) →collision on the surrounding molecular clouds.    then  s  Aharonian & Neronov (2005): possible origins for the  -ray cut-off: →cut-off in the initial proton injection spectrum →cut-off originates from the competition between the injection of protons in the surrounding medium and their escape from the Central Molecular Zone (≈leaky box model with energy-dependent diffusion)  Models favoured by the observation of the  -ray diffuse emission along the Galactic plane (very well interpreted by cosmic rays interactions with giant molecular clouds, see Nature paper). p+p+ p+p+ p+p+ p+p+ molecular clouds        accretion disk Sgr A* Moriond Matthieu Vivier

Conclusions  Sgr A East is now spatially excluded: Sgr A* and G still remain as possible counterparts.  Curvature in the spectrum  No variability in the H.E.S.S. signal on timescales ranging from a few minutes to one year: →no flaring activity →no periodic modulation of the TeV flux (QPOs)  TeV emission decorrelated from the other wavelengths  Analysis and results soon published in A&A Moriond Matthieu Vivier

Conclusions  Sgr A East is now spatially excluded: Sgr A* and G still remain as possible counterparts.  Curvature in the spectrum  No variability in the H.E.S.S. signal on timescales ranging from a few minutes to one year: →no flaring activity →no periodic modulation of the TeV flux (QPOs)  TeV emission decorrelated from the other wavelengths  Analysis and results soon published in A&A Thank you!