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Multi-Wavelength observations of the Galactic Center

10 TeV. Multi-Wavelength observations of the Galactic Center. 300 meV. Observational signatures and characterisation of the central black hole. D. Rouan. The Galactic Centre.

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Multi-Wavelength observations of the Galactic Center

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  1. 10 TeV Multi-Wavelength observations of the Galactic Center 300 meV Observational signatures and characterisation of the central black hole D. Rouan

  2. The Galactic Centre • 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 D. Rouan - LESIA - Obs. de Paris • 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)

  3. A supermassive Black Hole ? • 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 wavelengthsby a factor of 10-9 with respect to Eddington luminosityLEdd = 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

  4. The radio view : Sgr A* D. Rouan - LESIA - Obs. de Paris

  5. 0.9pc 2cm 3pc 7pc VLA 6cm The radio view : Sgr A* • 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) • A strongpoint source(Balik & Brown 74) : Sgr A* • no infrared nor X counterpart until 2000-2 • Non-thermal radiation (synchrotron) • variability : 2 typically (Brown & Lo, 82) D. Rouan - LESIA - Obs. de Paris

  6. Radio • The minicavity : a spherical void of 0.08 pcdiameter, 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 dustinside are probably heated byUV from the OB central cluster D. Rouan - LESIA - Obs. de Paris • 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. Radio size and spectrum of Sgr A* • 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) • 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) D. Rouan - LESIA - Obs. de Paris

  8. The X view • 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

  9. The X view = pre-Chandra/XMM era • 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* : Lx2-10 keV= 1035 erg s-1 • GRANAT : Lx35-150 keV < 6 1035 erg s-1 D. Rouan - LESIA - Obs. de Paris

  10. 1'.3 x 1'.5 And Chandra came... • 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 D. Rouan - LESIA - Obs. de Paris

  11. 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-lawN(E) = E-2.7 andNH = 1023 cm-2 • Or by a plasma w kT = 2 keV • Possible presence ofa Fe Ka line at 6-7 keV D. Rouan - LESIA - Obs. de Paris • Extension: • the source appears extendedw respect to point sources • qintrinsic = (q2 - qpsf2)1/2 = 0".6  .024 pc • Variability : statistically proven on 1h scale

  12. Non-BH possible X sources • 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

  13. 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 X Flares • First flare : • Chandra Oct 2000 • Baganoff et al. 01 • Duration : 104 s • N(E)  E-1.0 • Fastest variation : 10min D. Rouan - LESIA - Obs. de Paris

  14. XMM : Porquet et al. (04) XMM : Goldwurm et al. (03) Flares spectrum • 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) D. Rouan - LESIA - Obs. de Paris

  15. 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 : D. Rouan - LESIA - Obs. de Paris

  16. Whipple(Kosack & al 04) Hess(Aharonian 04) The gamma view • TeV emission detected by Whipple • 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 D. Rouan - LESIA - Obs. de Paris

  17. Onera + Obs. de Paris + Obs. De Grenoble The Infrared View • Search for : • 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" D. Rouan - LESIA - Obs. de Paris NAOS/CONICA on Yepun VLT-ESO

  18. IR : 1- dynamical signature • Follow-up of several stars during 10 years • 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 D. Rouan - LESIA - Obs. de Paris • 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 Mpc-3

  19. Excluded models • Recent refinement of orbits determination • Ghez et al. 05 : simultaneous constraint from7 stars orbits • M = 3.7 ± 0.2 M • position accuracy : 1.3 mas • Closest approach : 40 AU ! • Even more constraint on a point mass D. Rouan - LESIA - Obs. de Paris • 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

  20. Clénet & al 04 IR : 2 - the thermal IR emission • 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* D. Rouan - LESIA - Obs. de Paris

  21. Comparison to predicted spectra Yuan et al., 2003 NACO NACO D. Rouan - LESIA - Obs. de Paris Relativist Jet : synchrotron(radio/IR) + inverse self-compton (X) Accretion disk : synchrotron by thermal e- + inverse self-compton (X) + 5% of electrons accelerated Good agreement ! But…

  22. Clénet et al. 04 Ghez et al. 04 IR : 3 - variability, flashes • 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 D. Rouan - LESIA - Obs. de Paris

  23. Detection of infrared flares • May 03 : detection of a flare in H band (1.65µm) (Genzel et al.) • Followed by several (2 in K, 1 in L) • Flares Parameters : • typical duration : 90 min • frequency : 3 - 5 / day > X frequency(Chandra : 1.2 / day) • sub-period : 17 min D. Rouan - LESIA - Obs. de Paris

  24. Flare or Flash ? • In 2004 : several events detected • April: flare, • June : flare + short flash (<10 min), • Sept : flare • All observed in L' band (3.8 µm) D. Rouan - LESIA - Obs. de Paris Flare Sept 04 Flash Juin 04 Flare Juin 04

  25. Separation of flares and quiet mission • 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 • 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 ?

  26. 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 D. Rouan - LESIA - Obs. de Paris • 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)

  27. A simultaneous X / IR flare • 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

  28. Deconvolved L image K, L, M Images IR : 4 - Interaction with environnement ? • 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 D. Rouan - LESIA - Obs. de Paris • Another red elongated source • further away • with a bow shock appearance • ≈ in the same direction • no counterpart at Paschen a

  29. The overall picture • Taken from Aharonian 04 • Not so far from energy equipartition ... D. Rouan - LESIA - Obs. de Paris

  30. Summary • 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

  31. Summary • 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

  32. Conclusion • 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

  33. D. Rouan - LESIA - Obs. de Paris

  34. Paschen a vs L-M D. Rouan - LESIA - Obs. de Paris

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