Multi-Wavelength Multi-Wavelength observations of the observations of the

Galactic CenterGalactic Center

D. Rouan

Observational signatures and characterisation of the central black hole

10 TeV

300 meV

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At 8kpc, the GC region is totally At 8kpc, the GC region is totally hidden hidden in the visible in the visible by galactic dust by galactic dust (extinction by a factor (extinction by a factor 1 billion1 billion !) !)

• Fortunately it is seen in Fortunately it is seen in radio, infrared, X and radio, infrared, X and

The Galactic Centre The Galactic Centre

Star density : Star density : 10 million10 million times the solar neighbourhood ! times the solar neighbourhood ! A complex area : ionized and A complex area : ionized and

molecular gas, fast streams, molecular gas, fast streams, very hot gas, bubbles, relativistic very hot gas, bubbles, relativistic electrons, ...electrons, ...

L-M map (NACO)

Very young stars (10Very young stars (1066 years) and years) and evolved stars coexist in a evolved stars coexist in a small volumesmall volume

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4A supermassive Black Hole ?A supermassive Black Hole ? The GC area exhibits what is probably the The GC area exhibits what is probably the most evident most evident

concentration of dark massconcentration of dark mass Coincident with the radio source Sgr A*Coincident with the radio source Sgr A* Given the small distance : Given the small distance : the best candidate to test the the best candidate to test the

supermassive black hole paradigmsupermassive 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 luminosityLLEddEdd = 4 10 = 4 1037 37 WW (= 1.3 10 (= 1.3 103131 M/M M/M for M = 3 10 for M = 3 106 6 MM))

LLobsobs ≈ 10 ≈ 102828 W 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)

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5The radio view : Sgr A*The radio view : Sgr A*

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6The radio view : Sgr A*The radio view : Sgr A*• Extended emission (Yusef-Zadeh et al. 92):Extended emission (Yusef-Zadeh et al. 92):

• Mini spiralMini spiral structure with 3 arms extending structure with 3 arms extending on ≈ 3pc : Sgr A West on ≈ 3pc : Sgr A West rotating at 150 km/s around Sgr A* rotating at 150 km/s around Sgr A*

• A more diffuse ≈ spherical component A more diffuse ≈ spherical component extending to the East : likely a young extending to the East : likely a young (10(1044 yr) SN remnant (Melia 02) yr) SN remnant (Melia 02)

7pc

0.9pc

2cm

• A strongA strong point sourcepoint source (Balik & Brown 74) : Sgr A* (Balik & Brown 74) : Sgr A* • no infrared nor X counterpart until 2000-2no infrared nor X counterpart until 2000-2• Non-thermal radiation (Non-thermal radiation (synchrotronsynchrotron))• variability :variability : 2 typically 2 typically (Brown & Lo, 82)(Brown & Lo, 82)

3pc

VLA 6cm

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7Radio Radio • TheThe minicavity minicavity : a spherical void of 0.08 pc: a spherical void of 0.08 pc

diameter, very close to Sgr A* : may be due diameter, very close to Sgr A* : may be due to a focused flow from it to a focused flow from it

• The mini-spiral is inside a cavity The mini-spiral is inside a cavity delineated by a ring or shell of delineated by a ring or shell of molecular gas : hot gas and dustmolecular gas : hot gas and dustinside are probably heated byinside are probably heated byUV from the OB central clusterUV from the OB central cluster

• The overall dynamics in radio =>The overall dynamics in radio =>suggests a suggests a point mass of 3 10point mass of 3 1066 M M

at the center (Genzel & Townes, 87)at the center (Genzel & Townes, 87)

• Once corrected from galactic Once corrected from galactic

rotation, the rotation, the proper motionproper motion of Sgr A* of Sgr A* is is only 15 km/sonly 15 km/s (Reid et al. 99) : thus (Reid et al. 99) : thus at the very center of the Galaxyat the very center of the Galaxy

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8Radio size and spectrum of Sgr A*Radio size and spectrum of Sgr A*

Spectrum : Spectrum :

• Power-law with a significant millimeter excessPower-law with a significant millimeter excess

• agrees well with agrees well with synchrotron from plasma at 10synchrotron from plasma at 1011 11 KK (Radiatively Inefficient (Radiatively Inefficient Accretion Flow)Accretion Flow)

Polarization :Polarization :

• Linear and circular Linear and circular • Variable Variable (Bower et al 05)(Bower et al 05)

Radio size : observations at 3 and 1.4 mm demonstrate thatRadio size : observations at 3 and 1.4 mm demonstrate that Sgr A* Sgr A* size is below 0.1 massize is below 0.1 mas = 0.8 AU = 11 R = 0.8 AU = 11 RSchwSchw (for (for M = 3 10M = 3 106 6 MM))

Minimum size = 0.1 AU (1.2 RMinimum size = 0.1 AU (1.2 RSchwSchw) : set by maximum brightness ) : set by maximum brightness temperature at Compton limit (10temperature at Compton limit (101212 K) K)

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9The X viewThe X view

Expected X luminosity if at 10% of the Eddington Expected X luminosity if at 10% of the Eddington luminosity = 4 10luminosity = 4 104343 erg s erg s-1-1

Actually : LActually : Lxx(2-10keV) < 10(2-10keV) < 103535 erg s erg s-1 -1

The The 101099 discrepancy discrepancy is one of the most challenging issue is one of the most challenging issue in high energy astrophysics :in high energy astrophysics :

• Low accretion rate ?Low accretion rate ?

• Extremely low radiative efficiency ?Extremely low radiative efficiency ?

• Anisotropy or strong absorption of the emission ?Anisotropy or strong absorption of the emission ?

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10The X view = pre-Chandra/XMM eraThe X view = pre-Chandra/XMM era

Until the advent of Chandra and XMM, the only X flux Until the advent of Chandra and XMM, the only X flux detected revealed to be a combination of diffuse detected revealed to be a combination of diffuse emission and stellar sources :emission and stellar sources :

• ROSAT : one source within 10” of SgrA* : LROSAT : one source within 10” of SgrA* : Lxx = 7 10 = 7 103535 erg serg s-1-1

• ASCA : bright diffuse emission of hot gas (10 keV) ASCA : bright diffuse emission of hot gas (10 keV) associated to SgrA East shell : Lassociated to SgrA East shell : Lxx = 10 = 103636 erg s erg s-1-1

• BeppoSAX : diffuse BeppoSAX : diffuse emissionemission identified identified upper limit for Sgr A* : upper limit for Sgr A* : LLxx 2-10 keV2-10 keV= 10= 103535 erg s erg s-1-1

• GRANAT : GRANAT : LLxx 35-150 keV35-150 keV < 6 10 < 6 103535 erg s erg s-1-1

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11And Chandra came...And Chandra came...

Chandra (Baganoff et al. 2000, 2003) :Chandra (Baganoff et al. 2000, 2003) :

• Astrometry : 0".16 (Tycho sources)Astrometry : 0".16 (Tycho sources)

• 0.5-7 keV : diffuse emission + 119 point sources0.5-7 keV : diffuse emission + 119 point sources

• One source coincident with SgrA* within 0".27One source coincident with SgrA* within 0".27

1'.3 x 1'.5

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12Sgr A* in XSgr A* in X

2-10 keV luminosity : 2.4 (1.8-5.4) 102-10 keV luminosity : 2.4 (1.8-5.4) 103333 erg s erg s-1-1

Spectrum :Spectrum :

• Well fitted by an Well fitted by an absorbed power-lawabsorbed power-lawN(E) = N(E) = EE--2.72.7 and andNNHH = 10 = 102323 cm cm-2-2

• Or by a plasma w kT = 2 keVOr by a plasma w kT = 2 keV

• Possible presence ofPossible presence ofa Fe Ka Fe K line at 6-7 keV line at 6-7 keV

Extension: Extension:

• the source appears the source appears extendedextended w respect to point sources w respect to point sources

• intrinsicintrinsic = ( = (22 - - psfpsf22))1/21/2 = 0".6 = 0".6 .024 pc .024 pc

Variability : statistically proven on 1h scaleVariability : statistically proven on 1h scale

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13Non-BH possible X sources Non-BH possible X sources

Confusion w HeI/HI Confusion w HeI/HI emission line starsemission line stars (≈ LBV or WR star) ? (≈ LBV or WR star) ?

• No such star closer than 1.2"No such star closer than 1.2"

• Soft spectrum of W-R stars : cannot penetrate through the deep Soft spectrum of W-R stars : cannot penetrate through the deep obscurationobscuration

Colliding windsColliding winds of binary system including a W-R star ? of binary system including a W-R star ?

• Harder spectrumHarder spectrum

• Variability on days to years rather than hoursVariability on days to years rather than hours Low mass Low mass YSOYSO ? ?

• X-ray increase by 10-10X-ray increase by 10-1044 during first 10 during first 1077 years years

• If 100 such stars within 0".5 of SgrA * : X luminosity could be If 100 such stars within 0".5 of SgrA * : X luminosity could be explained, but mass segregation and IMF would not favor such a explained, but mass segregation and IMF would not favor such a numbernumber

A cluster of A cluster of X-ray binariesX-ray binaries in the cusp ? in the cusp ?

• Velocity dispersion (100 km sVelocity dispersion (100 km s-1-1) : very few at a given time) : very few at a given time

• Collisions : short lifetime of a binary system Collisions : short lifetime of a binary system

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14X FlaresX Flares

Baganoff et al. 2000, 2001,2003, Porquet et al. 2003

May 2002 campaign: ~0.6-1.2 flares/day

2-8 keV

2 hours2 hours

10 minutes10 minutes

First flare : First flare : • Chandra Oct 2000Chandra Oct 2000

• Baganoff et al. 01Baganoff et al. 01

• Duration : 10Duration : 1044 s s

• N(E) N(E) E E-1.0-1.0

• Fastest variation : 10minFastest variation : 10min

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15 Flares spectrumFlares spectrum

Typical duration : 2500sTypical duration : 2500s

• Short scale : 10 minShort scale : 10 min

• a few Ra few RSchwSchw

Hardness : Hardness : 2 behaviours :2 behaviours :

• Goldwurm et al. (03) - XMM : Goldwurm et al. (03) - XMM : flare with photon index flare with photon index = 0.9, = 0.9, thus harder than the thus harder than the = 2.7 of = 2.7 of quiescent statequiescent state

• Porquet et al. (03) - XMM : Porquet et al. (03) - XMM : a very bright flare remaining soft a very bright flare remaining soft (( = 2.5) = 2.5)

XMM : Goldwurm et al. (03)XMM : Goldwurm et al. (03)

XMM : Porquet et al. (04)XMM : Porquet et al. (04)

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16The gamma viewThe gamma view

Soft Soft rays detected by EGRET rays detected by EGRET

• Strong source of >100 MeV ≈ in Sgr A* directionStrong source of >100 MeV ≈ in Sgr A* direction

• BUT recent re-analyze : EGRET source is BUT recent re-analyze : EGRET source is offset (probability to be Sgr A* < 5%)offset (probability to be Sgr A* < 5%)

INTEGRAL : hard-X & soft INTEGRAL : hard-X & soft rays rays• 20-40 and 40-100 keV map at 12' resolution20-40 and 40-100 keV map at 12' resolution

• A A hard sourcehard source coincident within 1' w coincident within 1' w Sgr A*Sgr A*

• 20-40 keV : 1.9 ± 0.4 erg cm20-40 keV : 1.9 ± 0.4 erg cm-2-2 s s-1-1 (3.2 mcrab) (3.2 mcrab)

• 40-100 keV : 1.9 ± 0.4 erg cm40-100 keV : 1.9 ± 0.4 erg cm-2-2 s s-1-1 (3.4 mcrab) (3.4 mcrab)

• Possible variability or flare (Possible variability or flare (12) of 40 min :12) of 40 min :

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17The gamma viewThe gamma view

TeV emission detected by WhippleTeV emission detected by Whipple• unique Cherenkov telescopeunique Cherenkov telescope

• First evidence for TeV emission (97) First evidence for TeV emission (97)

Hess(Aharonian 04)

Whipple(Kosack & al 04)

TeV TeV rays emission detected by HESS rays emission detected by HESS• 2/4 Cherenkov telescopes2/4 Cherenkov telescopes

• rays excessrays excess at 14" ± 30" from at 14" ± 30" from Sgr A* Sgr A*

• Spectrum : ESpectrum : E2 2 dE/dN = 2.5 10dE/dN = 2.5 10-8-8 E E-.5 -.5 TeV mTeV m-2-2ss-1-1

• Conflict w CANGAROO measurements of larger flux Conflict w CANGAROO measurements of larger flux and softer spectrum => variability ? not and softer spectrum => variability ? not really predicted by various modelsreally predicted by various models

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18The Infrared ViewThe Infrared View

Search for : Search for : • dynamicaldynamical signature signature

• IR emission from disk, jet, accreting matter IR emission from disk, jet, accreting matter ++ variability variability, , flaresflares

• InteractionInteraction of jet of jet withwith its its environmentenvironment

Confusion is the issue Confusion is the issue adaptive optics the solution ! adaptive optics the solution ! diffrdiffr < 0.15" < 0.15"

NAOS/CONICA on NAOS/CONICA on YepunYepun VLT-ESO VLT-ESO

Onera + Obs. de Paris + Obs. De Grenoble

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19IR : 1- dynamical signature IR : 1- dynamical signature

Follow-up of several stars during 10 years Follow-up of several stars during 10 years • Very Very goodgood radio/IR radio/IR astrometryastrometry thanks to SiO masers of giant stars thanks to SiO masers of giant stars

• Orbit of several Orbit of several stars stars belonging to the very central cluster (<1")belonging to the very central cluster (<1")

• ESO program : MPE-Garching (Genzel et al.) + Lesia since 4 years ESO program : MPE-Garching (Genzel et al.) + Lesia since 4 years

• Keck program : A. GhezKeck program : A. Ghez NAOS/CONICA measurements : NAOS/CONICA measurements :

• Infrared wavefront sensor : IRS7, 6” at Nord : very good correction in KInfrared wavefront sensor : IRS7, 6” at Nord : very good correction in K

• angular resolution = 0.055"angular resolution = 0.055"

• Orbit of star S2Orbit of star S2 gravity probe with closest approach gravity probe with closest approach

at at 17 light-hour = 3 17 light-hour = 3 Sun-Pluto Sun-Pluto However beyond distance of tidal However beyond distance of tidal

disruption disruption

+ radio => 1019 Mpc-3

• Best mass distribution : Best mass distribution : a point a point mass M = 3.6 10mass M = 3.6 1066 M M

+ stellar cluster R+ stellar cluster Rcc= 0.34 pc, = 0.34 pc, = 4 10 = 4 1066 M M pcpc-3-3

• Hard to avoid identifying SgrA* Hard to avoid identifying SgrA* with a Black Hole !with a Black Hole !

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22Excluded models Excluded models

Recent refinement of orbits determination • Ghez et al. 05 : simultaneous constraint from

7 stars orbits

• M = 3.7 ± 0.2 MM

• 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

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IR : 2 - the thermal IR emission IR : 2 - the thermal IR emission Detection at L' (3.8 µm) of a possible IR counterpart (Ghez & al 04, Detection at L' (3.8 µm) of a possible IR counterpart (Ghez & al 04,

Clénet & al 04), when S2 was nearbyClénet & al 04), when S2 was nearby First detection at M (4.8 µm) (Clénet et al. 04) First detection at M (4.8 µm) (Clénet et al. 04)

• Very red color Very red color

• Spectroscopy of S2 (Ghez, 2003) : O or B star Spectroscopy of S2 (Ghez, 2003) : O or B star no confusion no confusion

• Since then, S2 moved : no more ambiguity Since then, S2 moved : no more ambiguity Astrometry : source w IR excess within 30 mas of SgrA* Astrometry : source w IR excess within 30 mas of SgrA*

Clénet & al 04Clénet & al 04

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Comparison to predicted spectra Comparison to predicted spectra

Accretion disk : synchrotron by thermal e- + inverse self-compton (X)

Relativist Jet : synchrotron(radio/IR) + inverse self-compton (X)

Good agreement !Good agreement !But…But…

Yuan et al., 2003

+ 5% of electrons accelerated

NACO

NACO

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25IR : 3 - variability, flashesIR : 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

Ghez et al. 04

Clénet et al. 04

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Detection of infrared flares 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

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27Flare or Flash ?Flare or Flash ?

In 2004 : several events detected In 2004 : several events detected • April: flare, April: flare,

• June : June : flareflare + short + short flashflash (<10 min), (<10 min),

• Sept : flare Sept : flare All observed in L' band (3.8 µm)All observed in L' band (3.8 µm)

Flash Juin 04Flare Sept 04

Flare Juin 04

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28 Separation of flares and quiet mission Separation of flares and quiet mission

Recent images : the quiet emission is resolved at ≈ 600 AU 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 photo-centre moves : during a flare/flash it is precisely on Sgr A* while

the quiet emission is offset by 40 mas to the SWthe quiet emission is offset by 40 mas to the SW

The quiet emission could correspond to synchrotron of a jet and flares to The quiet emission could correspond to synchrotron of a jet and flares to accretion events on the horizon of the BHaccretion events on the horizon of the BH

Question : can a low luminosity jet be extended on ≈ 300 AU ? Question : can a low luminosity jet be extended on ≈ 300 AU ?

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Flares : what constraint do they bring?Flares : what constraint do they bring?• Spectrum looks « blue »• Energy in IR flares ≈ X• tvar= few min r < 10 Rschw

• If synchrotron : accelerating event (= 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 Matter of the disk should accumulate on the LSO (Last Stable Orbit) : the LSO (Last Stable Orbit) :

• in Schwarzschild metric : T = 27 minin Schwarzschild metric : T = 27 min• In Kerr metric (rotating BH) : T= 17 min, In Kerr metric (rotating BH) : T= 17 min, if J/(GM/c) = 0.52 if J/(GM/c) = 0.52 maximum spin maximum spin

• Proposal (Genzel et al. 03) : the 17 min Proposal (Genzel et al. 03) : the 17 min pseudo-period could be the LSO pseudo-period could be the LSO the BH the BH one = 13 minone = 13 min

• Could be the 1Could be the 1stst measure of a BH spin, measure of a BH spin, one of the 3 parameters caracterizing a one of the 3 parameters caracterizing a BH (masse M, spin J, charge Q)BH (masse M, spin J, charge Q)

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30A simultaneous X / IR flareA simultaneous X / IR flare

Simultaneous observation of a flare in X (Chandra) and IR (NACO)Simultaneous observation of a flare in X (Chandra) and IR (NACO)• Eckart et al. (04) : Eckart et al. (04) :

• Well explained by SSC (Synchrotron Self Compton) from a component Well explained by SSC (Synchrotron Self Compton) from a component at a few Rat a few RSchwSchw

• SS-1.3-1.3

• Time Lag < 15 minTime Lag < 15 min

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K, L, M Images

IR : 4 - Interaction with environnement ?IR : 4 - Interaction with environnement ?

A jet colliding the ISM should leave A jet colliding the ISM should leave traces : host dust, shock signaturetraces : host dust, shock signature

A very red source close to SgrA* (.025 pc)A very red source close to SgrA* (.025 pc)

• elongated to SgrA*elongated to SgrA*

• TTcolcol = 650-800 K : = 650-800 K : hot dust hot dust

Deconvolved L image

Another red elongated source Another red elongated source

• further away further away

• with a bow shock appearancewith a bow shock appearance

• ≈ ≈ in the same directionin the same direction

• no counterpart at Paschen no counterpart at Paschen

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32The overall pictureThe overall picture

Taken from Taken from Aharonian 04 Not so far from energy equipartition ... Not so far from energy equipartition ...

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33SummarySummary

At At allall wavelengths from gamma to radio, there are now wavelengths from gamma to radio, there are now compelling evidences that a massive black hole is sitting compelling evidences that a massive black hole is sitting at the very center of the Galaxyat the very center of the Galaxy..

RadioRadio : :

• unresolved sourceunresolved source at scale of 1 UA (=11 R at scale of 1 UA (=11 Rschwschw),),

• TTbrightness brightness size size .1 AU (1. R .1 AU (1. Rschwschw))

• Spectrum ≈ synchrotron from plasma at 10Spectrum ≈ synchrotron from plasma at 101111K K

• Dynamics of the gasDynamics of the gas compact mass of 3 10 compact mass of 3 106 6 MM

• Very small proper motion Very small proper motion X rays : X rays :

• A A counterpartcounterpart to Sgr A* within 0.2" to Sgr A* within 0.2"

• Very intense Very intense flares and variability : d < 10 Rflares and variability : d < 10 RSchwSchw

• Radio/X connection : Radio/X connection : Synchrotron Self ComptonSynchrotron Self Compton

• No plausible alternate explanationNo plausible alternate explanation

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34SummarySummary

Gamma rays :Gamma rays :

• INTEGRAL : INTEGRAL : 20-110 keV source20-110 keV source coincident w Sgr A* coincident w Sgr A*

• HESS : HESS : TeV emissionTeV emission coincident w Sgr A* coincident w Sgr A* Infrared :Infrared :

• Stellar orbits determination Stellar orbits determination withinwithin 1 arcsec: 1 arcsec: Center of mass position accuracy : 1.3 masCenter of mass position accuracy : 1.3 mas Mass distribution implies a point mass of 3.7 Mass distribution implies a point mass of 3.7 MM 40 AU closest encounter 40 AU closest encounter excludes a dark clusterexcludes a dark cluster

• IR emission : IR emission : 3.8 and 4.8 µm 3.8 and 4.8 µm IR sourceIR source : on Sgr A* within 0.01" : on Sgr A* within 0.01" Flux level fits very well expected spectrumFlux level fits very well expected spectrum Flares and flashesFlares and flashes from 1.6 to 3.8 µm : on Sgr A* from 1.6 to 3.8 µm : on Sgr A* Simultaneous X and IR flareSimultaneous X and IR flare Quiet emission : slightly extended and offsetQuiet emission : slightly extended and offset

• Possible traces of a jet interactionPossible traces of a jet interaction with MIS with MIS

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35ConclusionConclusion

The last 4 years brought an harvest exciting key The last 4 years brought an harvest exciting key observational results (X, Gamma, IR)observational results (X, Gamma, IR)

The supermassive The supermassive BLACK HOLE PARADIGMBLACK HOLE PARADIGM at center at center of galaxies is now of galaxies is now HARDLY ESCAPABLEHARDLY ESCAPABLE

All results point to an All results point to an EXTRAORDINARY LOW EXTRAORDINARY LOW LUMINOSITYLUMINOSITY of the GC BH environment. of the GC BH environment. WHY ?WHY ?

The The FLAREFLARE phenomenon is likely phenomenon is likely THE KEY TO REACH THE KEY TO REACH THE HORIZONTHE HORIZON of the BH of the BH

Need for :Need for :

• Simultaneous observationsSimultaneous observations in in , X, IR, radio, X, IR, radio Should constrain models on flare mechanism Should constrain models on flare mechanism

• Even Even higher resolutionhigher resolution : : interferometry in the IRinterferometry in the IR XEUS, ...XEUS, ...

• More More predictionspredictions from models to test observationally from models to test observationally

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Paschen a vs L-MPaschen a vs L-M