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10 TeV Multi-Wavelength observations of the Galactic Center 300 meV Observational signatures and characterisation of the central black hole D. Rouan D. Rouan - LESIA - Obs. de Paris 16/03/05 The Galactic Centre 2 At 8kpc, the GC region is totally hidden in the visible by galactic dust (extinction by a factor 1 billion !) • Fortunately it is seen in radio, infrared, X and g Star density : 10 million times the solar neighbourhood ! A complex area : ionized and molecular gas, fast streams, very hot gas, bubbles, relativistic electrons, ... Very young stars (106 years) and evolved stars coexist in a small volume L-M map (NACO) D. Rouan - LESIA - Obs. de Paris 16/03/05 A supermassive Black Hole ? 4 The GC area exhibits what is probably the most evident concentration of dark mass Coincident with the radio source Sgr A* Given the small distance : the best candidate to test the supermassive black hole paradigm One might expect that Sgr A* should be a bright source, yet it is underluminous at all wavelengths by a factor of 10-9 with respect to Eddington luminosity LEdd = 4 1037 W (= 1.3 1031 M/M for M = 3 106 M) Lobs ≈ 1028 W Any clue that indeed a BH is there or is unlikely is welcome : this has been, and still is, the object of an active multi-wavelengths quest Recent review : Melia & Falcke (2001, ARAA) D. Rouan - LESIA - Obs. de Paris 16/03/05 The radio view : Sgr A* 5 D. Rouan - LESIA - Obs. de Paris 16/03/05 The radio view : Sgr A* 6 • Extended emission (Yusef-Zadeh et al. 92): • Mini spiral structure with 3 arms extending on ≈ 3pc : Sgr A West rotating at 150 km/s around Sgr A* • A more diffuse ≈ spherical component extending to the East : likely a young (104 yr) SN remnant (Melia 02) 0.9pc 2cm • A strong point source (Balik & Brown 74) : Sgr A* • no infrared nor X counterpart until 2000-2 • Non-thermal radiation (synchrotron) • variability : 2 typically (Brown & Lo, 82) 3pc 7pc VLA 6cm D. Rouan - LESIA - Obs. de Paris 16/03/05 Radio • The minicavity : a spherical void of 0.08 pc diameter, very close to Sgr A* : may be due to a focused flow from it • The mini-spiral is inside a cavity delineated by a ring or shell of molecular gas : hot gas and dust inside are probably heated by UV from the OB central cluster • The overall dynamics in radio => suggests a point mass of 3 106 M at the center (Genzel & Townes, 87) • Once corrected from galactic rotation, the proper motion of Sgr A* is only 15 km/s (Reid et al. 99) : thus at the very center of the Galaxy 7 D. Rouan - LESIA - Obs. de Paris 16/03/05 Radio size and spectrum of Sgr A* 8 Radio size : observations at 3 and 1.4 mm demonstrate that Sgr A* size is below 0.1 mas = 0.8 AU = 11 RSchw (for M = 3 106 M) Minimum size = 0.1 AU (1.2 RSchw) : set by maximum brightness temperature at Compton limit (1012 K) Spectrum : • Power-law with a significant millimeter excess • agrees well with synchrotron from plasma at 1011 K (Radiatively Inefficient Accretion Flow) Polarization : • Linear and circular • Variable (Bower et al 05) D. Rouan - LESIA - Obs. de Paris 16/03/05 The X view 9 Expected X luminosity if at 10% of the Eddington luminosity = 4 1043 erg s-1 Actually : Lx(2-10keV) < 1035 erg s-1 The 109 discrepancy is one of the most challenging issue in high energy astrophysics : • Low accretion rate ? • Extremely low radiative efficiency ? • Anisotropy or strong absorption of the emission ? D. Rouan - LESIA - Obs. de Paris 16/03/05 The X view = pre-Chandra/XMM era 10 Until the advent of Chandra and XMM, the only X flux detected revealed to be a combination of diffuse emission and stellar sources : • ROSAT : one source within 10” of SgrA* : Lx = 7 1035 erg s-1 • ASCA : bright diffuse emission of hot gas (10 keV) associated to SgrA East shell : Lx = 1036 erg s-1 • BeppoSAX : diffuse emission identified upper limit for Sgr A* : Lx 2-10 keV= 1035 erg s-1 • GRANAT : Lx 35-150 keV < 6 1035 erg s-1 D. Rouan - LESIA - Obs. de Paris 16/03/05 And Chandra came... 11 Chandra (Baganoff et al. 2000, 2003) : • Astrometry : 0".16 (Tycho sources) • 0.5-7 keV : diffuse emission + 119 point sources • One source coincident with SgrA* within 0".27 1'.3 x 1'.5 D. Rouan - LESIA - Obs. de Paris 16/03/05 Sgr A* in X 2-10 keV luminosity : 2.4 (1.8-5.4) 1033 erg s-1 Spectrum : • Well fitted by an absorbed power-law N(E) = E-2.7 and NH = 1023 cm-2 • Or by a plasma w kT = 2 keV • Possible presence of a Fe Ka line at 6-7 keV Extension: • the source appears extended w respect to point sources • qintrinsic = (q2 - qpsf2)1/2 = 0".6 .024 pc Variability : statistically proven on 1h scale 12 D. Rouan - LESIA - Obs. de Paris 16/03/05 Non-BH possible X sources 13 Confusion w HeI/HI emission line stars (≈ LBV or WR star) ? • No such star closer than 1.2" • Soft spectrum of W-R stars : cannot penetrate through the deep obscuration Colliding winds of binary system including a W-R star ? • Harder spectrum • Variability on days to years rather than hours Low mass YSO ? • X-ray increase by 10-104 during first 107 years • If 100 such stars within 0".5 of SgrA * : X luminosity could be explained, but mass segregation and IMF would not favor such a number A cluster of X-ray binaries in the cusp ? • Velocity dispersion (100 km s-1) : very few at a given time • Collisions : short lifetime of a binary system D. Rouan - LESIA - Obs. de Paris 16/03/05 X Flares 14 First flare : • • • • • Chandra Oct 2000 Baganoff et al. 01 Duration : 104 s N(E) E-1.0 Fastest variation : 10min 2-8 keV 10 minutes 2 hours May 2002 campaign: ~0.6-1.2 flares/day Baganoff et al. 2000, 2001,2003, Porquet et al. 2003 D. Rouan - LESIA - Obs. de Paris 16/03/05 Flares spectrum 15 Typical duration : 2500s • Short scale : 10 min • a few RSchw Hardness : 2 behaviours : • Goldwurm et al. (03) - XMM : flare with photon index G = 0.9, thus harder than the G = 2.7 of quiescent state • Porquet et al. (03) - XMM : a very bright flare remaining soft (G = 2.5) XMM : Porquet et al. (04) XMM : Goldwurm et al. (03) D. Rouan - LESIA - Obs. de Paris 16/03/05 The gamma view Soft g rays detected by EGRET • • Strong source of >100 MeV ≈ in Sgr A* direction BUT recent re-analyze : EGRET source is offset (probability to be Sgr A* < 5%) INTEGRAL : hard-X & soft g rays • • • • • 20-40 and 40-100 keV map at 12' resolution A hard source coincident within 1' w Sgr A* 20-40 keV : 1.9 ± 0.4 erg cm-2 s-1 (3.2 mcrab) 40-100 keV : 1.9 ± 0.4 erg cm-2 s-1 (3.4 mcrab) Possible variability or flare (12) of 40 min : 16 D. Rouan - LESIA - Obs. de Paris 16/03/05 The gamma view TeV emission detected by Whipple • • 17 unique Cherenkov telescope First evidence for TeV emission (97) TeV g rays emission detected by HESS • • • • 2/4 Cherenkov telescopes g rays excess at 14" ± 30" from Sgr A* Spectrum : E2 dE/dN = 2.5 10-8 E-.5 TeV m-2s-1 Conflict w CANGAROO measurements of larger flux and softer spectrum => variability ? not really predicted by various models Hess (Aharonian 04) Whipple (Kosack & al 04) D. Rouan - LESIA - Obs. de Paris 16/03/05 The Infrared View Search for : • • • 18 dynamical signature IR emission from disk, jet, accreting matter + variability, flares Interaction of jet with its environment Confusion is the issue adaptive optics the solution ! qdiffr < 0.15" NAOS/CONICA on Yepun VLT-ESO Onera + Obs. de Paris + Obs. De Grenoble D. Rouan - LESIA - Obs. de Paris 16/03/05 IR : 1- dynamical signature Follow-up of several stars during 10 years • • • • 19 Very good radio/IR astrometry thanks to SiO masers of giant stars Orbit of several stars belonging to the very central cluster (<1") ESO program : MPE-Garching (Genzel et al.) + Lesia since 4 years Keck program : A. Ghez NAOS/CONICA measurements : • • • • • Infrared wavefront sensor : IRS7, 6” at Nord : very good correction in K angular resolution = 0.055" Orbit of star S2 gravity probe with closest approach at 17 light-hour = 3 Sun-Pluto However beyond distance of tidal disruption Best mass distribution : a point mass M = 3.6 106 M + stellar cluster Rc= 0.34 pc, r = 4 106 M pc-3 Hard to avoid identifying SgrA* with a Black Hole ! + radio => 1019 Mpc-3 D. Rouan - LESIA - Obs. de Paris 16/03/05 Excluded models 22 Recent refinement of orbits determination • Ghez et al. 05 : simultaneous constraint from • • • • 7 stars orbits M = 3.7 ± 0.2 M position accuracy : 1.3 mas Closest approach : 40 AU ! Even more constraint on a point mass Excluded Models : • • Dark stellar cluster (BD, neutron star, stellar BH ) : would impose a central density = 1017-19 M pc-3 lifetime < 105 years rejected Ball of fermions (neutrinos, gravitinos, axinos, …) finite size of 7000 UA > S2 perimelanophreas* rejected * From ancient greek : melano = black, phreas = well 16/03/05 IR : 2 - the thermal IR emission D. Rouan - LESIA - Obs. de Paris Detection at L' (3.8 µm) of a possible IR counterpart (Ghez & al 04, Clénet & al 04), when S2 was nearby First detection at M (4.8 µm) (Clénet et al. 04) • Very red color • Spectroscopy of S2 (Ghez, 2003) : O or B star no confusion • Since then, S2 moved : no more ambiguity Astrometry : source w IR excess within 30 mas of SgrA* Clénet & al 04 23 24 16/03/05 Comparison to predicted spectra D. Rouan - LESIA - Obs. de Paris Yuan et al., 2003 NACO NACO Accretion disk : synchrotron by thermal e+ inverse self-compton (X) + 5% of electrons accelerated Relativist Jet : synchrotron (radio/IR) + inverse self-compton (X) Good agreement ! But… D. Rouan - LESIA - Obs. de Paris 16/03/05 IR : 3 - variability, flashes 25 • Ghez et al. 04, Clénet et al. 04: between August 02 and June 03 : variation by a factor 2 of the L flux • Excludes in practice any confusion w a background star or a member of the young cluster Clénet et al. 04 Ghez et al. 04 16/03/05 • May 03 : detection of a flare in H band (1.65µm) (Genzel et al.) • Followed by several (2 in K, 1 in L) D. Rouan - LESIA - Obs. de Paris Detection of infrared flares • Flares Parameters : • typical duration : 90 min • frequency : 3 - 5 / day > X frequency (Chandra : 1.2 / day) • sub-period : 17 min 26 D. Rouan - LESIA - Obs. de Paris 16/03/05 Flare or Flash ? 27 In 2004 : several events detected • • • April: flare, June : flare + short flash (<10 min), Sept : flare All observed in L' band (3.8 µm) Flare Sept 04 Flare Juin 04 Flash Juin 04 28 Recent images : the quiet emission is resolved at ≈ 600 AU The photo-centre moves : during a flare/flash it is precisely on Sgr A* while the quiet emission is offset by 40 mas to the SW D. Rouan - LESIA - Obs. de Paris 16/03/05 Separation of flares and quiet mission The quiet emission could correspond to synchrotron of a jet and flares to accretion events on the horizon of the BH Question : can a low luminosity jet be extended on ≈ 300 AU ? D. Rouan - LESIA - Obs. de Paris 16/03/05 Flares : what constraint do they bring? • Spectrum looks « blue » • Energy in IR flares ≈ X • tvar= few min r < 10 Rschw • If synchrotron : accelerating event (g= 103), but issue of blue spectrum • If free-free (or BB) :accretion event of m = few 1019 g (≈ comet) • Polarization should bring an answer • Matter of the disk should accumulate on the LSO (Last Stable Orbit) : • in Schwarzschild metric : T = 27 min • In Kerr metric (rotating BH) : T= 17 min, if J/(GM/c) = 0.52 maximum spin • Proposal (Genzel et al. 03) : the 17 min pseudo-period could be the LSO the BH one = 13 min • Could be the 1st measure of a BH spin, one of the 3 parameters caracterizing a BH (masse M, spin J, charge Q) 29 D. Rouan - LESIA - Obs. de Paris 16/03/05 A simultaneous X / IR flare 30 Simultaneous observation of a flare in X (Chandra) and IR (NACO) • • • • Eckart et al. (04) : Well explained by SSC (Synchrotron Self Compton) from a component at a few RSchw Sn n-1.3 Time Lag < 15 min D. Rouan - LESIA - Obs. de Paris 16/03/05 IR : 4 - Interaction with environnement ? 31 Deconvolved L image A jet colliding the ISM should leave traces : host dust, shock signature A very red source close to SgrA* (.025 pc) • elongated to SgrA* • Tcol = 650-800 K : hot dust Another red elongated source • further away • with a bow shock appearance • ≈ in the same direction • no counterpart at Paschen a K, L, M Images 16/03/05 The overall picture D. Rouan - LESIA - Obs. de Paris Taken from Aharonian 04 Not so far from energy equipartition ... 32 D. Rouan - LESIA - Obs. de Paris 16/03/05 Summary 33 At all wavelengths from gamma to radio, there are now compelling evidences that a massive black hole is sitting at the very center of the Galaxy. Radio : • unresolved source at scale of 1 UA (=11 Rschw), • Tbrightness size .1 AU (1. Rschw) • Spectrum ≈ synchrotron from plasma at 1011K • Dynamics of the gas compact mass of 3 106 M • Very small proper motion X rays : • A counterpart to Sgr A* within 0.2" • Very intense flares and variability : d < 10 RSchw • Radio/X connection : Synchrotron Self Compton • No plausible alternate explanation D. Rouan - LESIA - Obs. de Paris 16/03/05 Summary 34 Gamma rays : • INTEGRAL : 20-110 keV source coincident w Sgr A* • HESS : TeV emission coincident w Sgr A* Infrared : • Stellar orbits determination within 1 arcsec: Center of mass position accuracy : 1.3 mas Mass distribution implies a point mass of 3.7 M 40 AU closest encounter excludes a dark cluster • IR emission : 3.8 and 4.8 µm IR source : on Sgr A* within 0.01" Flux level fits very well expected spectrum Flares and flashes from 1.6 to 3.8 µm : on Sgr A* Simultaneous X and IR flare Quiet emission : slightly extended and offset • Possible traces of a jet interaction with MIS D. Rouan - LESIA - Obs. de Paris 16/03/05 Conclusion 35 The last 4 years brought an harvest exciting key observational results (X, Gamma, IR) The supermassive BLACK HOLE PARADIGM at center of galaxies is now HARDLY ESCAPABLE All results point to an EXTRAORDINARY LOW LUMINOSITY of the GC BH environment. WHY ? The FLARE phenomenon is likely THE KEY TO REACH THE HORIZON of the BH Need for : • Simultaneous observations in g, X, IR, radio Should constrain models on flare mechanism • Even higher resolution : interferometry in the IR XEUS, ... • More predictions from models to test observationally D. Rouan - LESIA - Obs. de Paris 16/03/05 36 D. Rouan - LESIA - Obs. de Paris 16/03/05 Paschen a vs L-M 37