1 EXCESS OF VHE COSMIC RAYS IN THE CENTRAL 100 PC OF THE MILKY WAY Léa Jouvin, A. Lemière and R. Terrier
2 Excess of VHE cosmic rays (CRs) γ-ray count map Matter traced by CS 150 pc After subtracting the brightest TeV sources: -> diffuse hadronic emission Credits: H.E.S.S. collaboration Aharonian et al., 2006 -> CRs energy density: 3-9 times higher than the local one and harder spectrum (Γ=2.3) 2
3 A unique accelerator in the central pc? 5.5 GHz SgrA East : - Supernovae remnant (SNR) - situated at ~ 2 pc from SgrA* - explosion ~ 10 000 years è Impulsive injection Credits: Zhao et al. 2016
4 A unique accelerator in the central pc? Credits: H.E.S.S. collaboration Abramowski et al., 2016 Compatible with a stationary source at the center è Require power: 10 38 erg s -1 SgrA*: Credits: H.E.S.S. collaboration Abramowski et al., 2006 Dissipated power: 10 39 erg s -1 (Wang et al,2013) è Good candidate for CR acceleration
5 Multiple CR impulsive injections Supernovae Remnant (SNR): CR acceleration up to the knee in the whole Galaxy Galactic Center: Ø 2% of the Galaxy s massive star formation Ø High supernova (SN) rate: 10-4 -10-3 yrs -1 (Crocker et al. 2011, Ponti et al. 2015) Ø Ė SN =3.2 10 39 3.2 10 40 erg s -1 What is the impact of these SNRs on the CR density and VHE emission in the GC? 5
CR escape: Advection or Diffusion? Steady state model 6
7 Advection vs diffusion Advection: perpendicular wind of speed v (Yoast-hull et al. 2014, Crocker et al 2011) v=1000 km/s τ adv = H/v è τ adv =30 000 yrs Diffusion: along the magnetic field lines D=D 10TeV (E/10 TeV) 0.3 D 10TeV =2 10 29 m 2 s -1 τ diff = H 2 /D è At 1 Tev, τ diff =600 yrs Diffusion more competitive than advection H=30 pc advection diffusion
8 Spectral energy distribution GAMERA (Hahn 2015) solves the following kinetic equation: advection SED all pion decay bremsstrahlung Intrinsic power-law spectrum: Q=Q 0 E -p Advection: t SN =10 000 yrs p=2.45 τ adv =30 000 yrs IC
9 Spectral energy distribution GAMERA (Hahn 2015) solves the following kinetic equation: Diffusion all SED bremsstrahlung pion decay IC Intrinsic power-law spectrum: Q=Q 0 E -p Diffusion: t SN = 2000 yrs p=2.15 At 1 Tev, τ diff =600 yrs
10 Spectral energy distribution GAMERA (Hahn 2015) solves the following kinetic equation: Diffusion all SED bremsstrahlung pion decay IC Intrinsic power-law spectrum: Q=Q 0 E -p Diffusion: t SN = 2000 yrs p=2.15 At 1 Tev, τ diff =600 yrs For high energy proton (> 1 TeV) τ diff < t SN : stationary state assumption incorrect
A simple time dependent 3D model CR injection and gamma-ray production 11
12 3D matter distribution Taken from Sawada et al (2004) Ø M tot =40 10 6 M sun, (1.2-6.4 10 7 M sun ) Dahmen et al. 1998, Oka et al. 2005, Sofue et al. 1995 Ø Exponential decay along the latitude (Ferriere et al. 2007) Top view b=0, from the direction of the north Galactic pole Credits: Sawada et al. 2004 12
Spatial distribution of the SNs filling the GC 13 Arches Central Cluster Quintuplet SgrA* 150 pc Credits: Ponti et al 2015 - Thermal emission concentrated in the central part of the GC: hot plasma at 1 kev - Three compact and massive clusters in the GC: the Quintuplet (3-5 Myrs), the Arches (2-3 Myrs) and the Central Cluster (4-6 Myrs) - Several independant observations shown the presence of a high number of isolated stars (Mauerhan et al. 2010) 13
14 3D SNs modeling Temporal distribution: Recurrence time: 2500 years, central value found in Crocker et al. (2011) Spatial distribution: Ø Two components: Uniform+ Clusters Ø IMF + total mass è SN rate in the two clusters: - Central: 0.3-1.2 10-4 yrs -1 (Lu et al. 2013) - Quintuplet: 0.3 10-4 yrs -1 (Hussmann et al. 2012)
15 CR diffusion Ø Punctual Injection: Intrinsic power-law spectrum Q= N o E -2 Ø Propagation: Transport equation D=D 10TeV (E/10 TeV) 0.3, D 10TeV =2 10 29 m 2 s -1 (interstellar medium value): Impulsive solution (SNRs): Stationary solution (SgrA*): Ø E CR : 1 TeV to 1 PeV 2D map (l,b) Integration along the line of sight Latitude b 15 longitude l
16 Profile and spectrum of the 3D emission comparaison with H.E.S.S. data
17 γ-rays: spectral distribution ϒ-rays spectrum dn/de (TeV -1 cm -2 s -1 sr -1 ) Median of the γ-rays profiles Dispersion around the median 0.15 0.45 Energy (ev) SNs: E SN : 10 51 erg Efficiency for CR acceleration: 2% Stationary source: Require power: 10 38 erg s -1
18 γ-rays: spectral distribution ϒ-rays spectrum dn/de (TeV -1 cm -2 s -1 sr -1 ) Median of the γ-rays profiles Dispersion around the median 0.15 0.45 Energy (ev) SNs: E SN : 10 51 erg Efficiency for CR acceleration: 2% Stationary source: Require power: 10 38 erg s -1
Gamma ray profile for the SNRs filling the GC γ-ray profile along the galactic longitude 19 Integrated flux (erg m 2 s -1 sr -1 ) Median of the γ-rays profiles Dispersion around the median longitude (degrees) Realistic distribution of SNRs (with the two clusters): è makes the distribution peaked toward the GC
20 γ-rays: spatial distribution γ-ray profile along the galactic longitude Integrated flux (erg m 2 s -1 sr -1 ) SgrB SgrA SgrC longitude (degrees)
21 CR density profile Credits: H.E.S.S. collaboration Abramowski et al., 2016 At distance >30pc: both model can explain the data Central excess seems difficult to be reproduced by the SNRs alone Stationary source alone: why SNRs doesn t accelerate CR in the GC?
22 Conclusion Ø CR acceleration from the SNRs can not be neglected: Already re(over)produce the total flux -> SNR efficiency? Realistic spatial distribution: -> gradient of CR density toward the GC -> VHE γ-ray profile peaked toward the GC need an extra VHE γ-ray central component Ø Single stationary accelerator at the center (Abramowski et al., 2016): fit very well data points Ø Not possible to conclude that SgrA* is the only source responsible for all the VHE emission observed with H.E.S.S. in the GC knowing the significant contribution of the SNe
Thanks for your attention 23
24 3D matter distribution Top view b=0, from the direction of the north Galactic pole Face on view