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Constraining the accretion flow evolution around the best intermediate mass black hole candidate HLX-1 in the ESO 243-49 galaxy Olivier Godet Collaborators D. Barret N. Webb T. Alexander V. Braito S. Corbel D. Cseh S.W. Davis G. Dubus S. Farrell R. Fender N. Gehrels A.J. Gosling I. Heywood T. Kawaguchi C. Knigge J.-P. Lasota E. Lenc D. Lin T. Maccarone C. Maraston C. Maraston R. Narayan S. R. Oates J. Pforr B. Plazolles M. Servillat K. Wiersema Y. Zhu Accretion Flow Instabilities 2012 Science rationale • Two varieties of BHs known: stellar-mass BH (3- ~20 M - e.g. Crowther et al. 2010, Belczynski et al. 2010, maybe up to ~80-90 M - e.g. Fryer 1999, Belczynski et al. 2004, 2010) supermassive BHs (106-1010 M , possibly down to a few x 105 M Peterson et al. 2005, Greene & Ho 2004, 2007) • The cosmological growth of supermassive BHs understanding the formation and evolution of galaxies. is a SMBH seeds proposed to be of intermediate masses (102-105 M - e.g. key to - Madau et al. 2001, Bellovary et al. 2011) Growth by IMBH mergers, gas accretion episodes / accreting stars (e.g. Bromley et al. 2012) Accretion Flow Instabilities 2012 Science rationale • Two varieties of BHs known: stellar-mass and supermassive BHs • The cosmological growth of supermassive BHs understanding the formation and evolution of galaxies. • IMBHs are also of great interest for: is a key to • detecting strong gravitational wave signals (e.g. Miller et Colbert 2004) & dark matter (Fornasa & Bertone 2008) • investigating the unification of some properties of accreting BHs of all masses • Do IMBHs exist? If so, where to search for them? • One possibility is in Ultra Luminous X-ray sources. Accretion Flow Instabilities 2012 Ultra Luminous X-ray sources • ULXs are X-ray sources exibiting LX > 3x1039 erg s-1. • ULXs are located outside the nucleus of their host galaxy (spiral & elliptical galaxies). • Most ULXs are thought to be accreting BHs. • Assuming spherical, steady accretion, LEdd (MBH ~ 20 M ) ~ 3x1039 erg s-1 • To avoid LX > LEdd, M should be in the IMBH range. • Soft components in some ULX spectra with kT ~ 0.2-0.3 keV may also provide evidence for IMBHs (e.g. Roberts 2007) Accretion Flow Instabilities 2012 Ultra Luminous X-ray sources • Not all ULXs contain IMBHs (Gao 2003, King 2004, Grimm et al. 2003, Walton et al. 2011, Roberts 2007) L T ~4 Kajava & Poutanen (2008) • Alternatives: Collimated emission (geometrical collimation – King et 2001, King 2008; relativistic boosting – Freeland et al. 2003) super- or critical Eddington accretion onto a stellar mass BH (e.g. Mizuno et al. 2001, Vierdayanti et al. 2006, Feng & Kaaret 2007, Kajava & Poutanen 2008, King 2009, Zampieri & Roberts 2009, Gladstone et al. 2009) Accretion Flow Instabilities 2012 Discovery of HLX-1 (Farrell et al. 2009) • Discovery made using the 2XMM catalogue (Watson et al. 2009) during a work to search for new compact objects HLX-1 • Name = 2XMM J011028.1-460421 (observation in 2004 Nov. 23) • Associated with the near-edge-on S0-type galaxy ESO 243-49 – 8” from nucleus •z galaxy = 0.0224 (i.e. 95 Mpc) • 9% chance for a random association HST image unabs 42 1 L 1 . 1 10 erg s • at 0.2 10keV most • Brightest detected ULX! • Source variable • Assuming L < 10xLEdd (Begelman 2002), M > 500 M Accretion Flow Instabilities 2012 Redshift measurement (Wiersema et al. 20120) • Chandra position with error circle of 0.3” (95% c.l.) – Webb et al. 2010 • Optical counterpart in R (23.8 mag) & V (24.5 mag) bands (Soria et al. 2010) FX/Fopt ratio ~ 1000 unlikely to be a background AGN (< 10) • VLT DDT in Nov.-Dec. 2009 to measure the redshift of HLX-1 Hα in absorption Galaxy HLX-1 Na ID in absorption Blend Fe I & Ca I line • Galaxy redshift = 0.0223 • At 6643Å, rest-frame 6497Å blend line well known to be associated to late G & early K stars – consistent with ~5-6 Gyr old stellar population from ESO 243-49 (Soria et al. 2010) Accretion Flow Instabilities 2012 Redshift measurement (Wiersema et al. 20120) Galaxy Galaxy HLX-1 HLX-1 11.3σ detection of a Hα line in emission at the position of HLX-1 only • Confirmation of HLX-1 distance (~95 Mpc using WMAP5 parameters) • Possible velocity offset ~ +170 km s-1 Accretion Flow Instabilities 2012 Spectral states Godet et al. (2012) GX339-4 Meyer-Hofmeister et al. (2009) • Hardness-Intensity track reminiscent of those in Galactic BH binaries, but at much brighter luminosity (L0.2-10 keV ~ 2x1040 - 1042 erg s-1) • BH nature in HLX-1 strengthened Accretion Flow Instabilities 2012 Spectral states (Godet et al. 2009; Servillat et al. 2011) • State transitions: soft-to-hard and hard-to-soft, XMM1 = steeppowerlaw state Accretion Flow Instabilities 2012 Detection of radio flares (Webb et al. 2012, Science) • Stellar-mass & supermassive BHs known to launch jets • Stellar-mass BH binaries known to show radio flares following the hard-to-soft transition (e.g. Körding et al. 2005) • 7 x 12 hrs ATCA observations at 5 & 9 GHz spread over 2 outbursts (Fender et al. 2004) (Webb et al. 2012, Science) • Stellar-mass & supermassive BHs known to launch jets • Stellar-mass BH binaries known to show radio flares following the hard-to-soft transition (e.g. Körding et al. 2005) Hard-to-soft transition • 7 x 12 hrs ATCA observations at 5 & 9 GHz spread over 2 outbursts Hard-to-soft transition Accretion Flow Instabilities 2012 Detection of radio flares Accretion Flow Instabilities 2012 Detection of radio flares Co-added 5+9 GHz detection: 8.2σ, F = 45 μJy (Webb et al. 2012, Science) All non detections (5+9 GHz): 3σ upper limit = 21 μJy • Detection of a variable radio emission following the hard-to-soft transition • Radio nebula as seen in some ULXs excluded • Data consistent with a transient jet ejection event • First ever detection of a jet event in a ULX! Accretion Flow Instabilities 2012 Constraining the BH mass • From peak luminosity and assuming hyper-accretion with LX < 10xLEdd (Begelman 2002), M > 500 M (Farrell et al. 2009) • Eddington scaling from Galactic BH sources: • Radio flares appear when LX ~10%-100% LEdd (e.g. Fender et al. 2004) 9200 < M < 92000 M (Webb et al. 2012) • Low hard state: LX ~ 1% LEdd M ~ 16000 M • Steep powerlaw state: LX ~ 100% LEdd (Servillat et al. 2011) M ~ 2x104 M (Servillat et al. 2011) • Soft-to-hard luminosity transition: LX ~ 1-4% LEdd (e.g. Maccarone 2003) 16000 < M < 25000 M • Dynamical measurements of the BH mass very challenging given the source distance (~95 Mpc) • Need to rely on some indirect ways to weigh the BH Accretion Flow Instabilities 2012 Constraining the BH mass • To detect a 6.4 keV Fe line (Gaussian) with EW = 30 eV, exposure time > 1 Ms with XMM – even worse for relativistic lines • Spectral fitting of the soft component by physically motivated accretion flow models: BHSPEC (Davis et al. 2005) & the SLIMDISK model (Kawaguchi 2003) • Motivation: • To put constraints on the BH mass & accretion flow • Both models applied to either Galactic BH sources or/and ULXs (e.g. for SLIMDISK, Foschini et al. 2006; Okajima et al. 2006 – Hui & Krolik for BHSPEC). • SLIMDISK = sub- and super-Eddington accretion regime - radial advection • Methodology: multi-epoch and multi-instrument (XMM, Swift-XRT & Chandra) spectral fitting within Xspec Accretion Flow Instabilities 2012 Results from Davis et al. (2011) • BHSPEC = relativistic sub-Eddington thin disk including Comptonization and electron opacity effects around a rotating BH (Davis et al. 2005) • Key parameters: M , a* 1,0.99, i 0o ,90o , l ( • Data selection: Swift1 LX ) 0.01,1, source distance LEdd Swift2 Accretion Flow Instabilities 2012 Results from Davis et al. (2011) • Large degeneracy due to lack of constraints on i & a* the BH mass by a factor of 100 uncertainty in 68% 90% 99% • XMM: 3000 M (i=0o, a*=-1, l=0.7) < M < 3x105 M (i=90o & a*=0.99) at 90% c.l. Assuming a binary system, i < 75o due to lack of eclipses & M < 105M • Swift & Chandra: a*< 0 & a* < -0.5 inconsistent with Swift & Chandra data, respectively. i , l ≥ 1 for sufficiently low a*. • All data: 6000 M (i=0o & l=1) < M • All BH mass estimates favour the IMBH solution. Accretion Flow Instabilities 2012 Results from Godet et al. (2012) • SLIMDISK = face-on (i=0o) sub- and super-Eddington accretion disks around a non-rotating (a*=0) BH (Kawaguchi 2003) • SLIMDISK includes relativistic and electron opacity effects, Comptonization & effects of radial advection (computed at every radii) • key parameters: L ( Edd M [3.2,105 ]M , m ) 1,1000& 0.01,1, source distance 2 c • Data selection: XMM, Chandra & Swift-XRT (over different intensity ranges) • Consistent mass estimate (90% level) between 3 instruments: 16000 M < M < 32000 M • SLIMDISK model also favours the IMBH solution. • Accretion flow radiating with an efficiency of η ~ 0.11 • At peak, 10 1 m • Otherwise, 10 m • Sub-Eddington accretion regime 0.01-20 keV unabs. luminosity (erg s-1) Accretion Flow Instabilities 2012 Results from Godet et al. (2012) Accretion rate (LEdd/c2) • Assuming an average BH mass of 18000 M , l ~ 1.1 at the peak Inner part of the disk is radiation-pressure dominated Kawaguchi (2003) Accretion Flow Instabilities 2012 Results from Godet et al. (2012) • Evolution of the accretion rate ~ 4 104 M • At peak, M yr -1 • “Plateau” around the peak lasting for 2-3 weeks with ~ 10 m Accretion Flow Instabilities 2012 Results from Godet et al. (2012) • Rapid decrease of the accretion rate towards the end of the outbursts Soft-to-hard state transition 4 106 M yr -1 • In low/hard, M Accretion Flow Instabilities 2012 Results from Godet et al. (2012) • Rapid decrease of the accretion rate towards the end of the outbursts Soft-to-hard state transition 4 106 M yr -1 • In low/hard, M • Inner parts of the disk switch to an ADAF geometry (e.g. Esin et al. 1997) ? • Innermost radius supposed to recede at larger radii in this case Accretion Flow Instabilities 2012 Results from Godet et al. (2012) • Evolution of the X-ray luminosity vs disk temperature L T 2.40.7(1 ) LT4 • Measured: • Computed: (1σ error) using η=0.11, RISCO=3RS & M = 18000 M Accretion Flow Instabilities 2012 How is the BH fed? (Lasota et al. 2011) ~1 yr ~1 yr ~1 yr • Swift-XRT monitoring since 2009 (> 600 ks) • FRED-like outbursts presence of reflares plateau phase at the peak (~2-3 weeks) • Recurrence timescale of nearly a year (~367 days) • Very steep rise (over a week) • Are HLX-1’s outbursts produced by a thermal-viscous instability as seen in X-ray transients & dwarf novae? • Answer: observed outburst timescales inconsistent with thermalviscous timescales Accretion Flow Instabilities 2012 How is the BH fed? (Lasota et al. 2011) • From the SLIMDISK & BHSPEC results, the inner part of the disk appears to be radiation-pressure dominated (LX > 0.06 LEdd). • Radiation-pressure dominated disk shown to be viscously and thermally unstable (e.g. Shakura & Sunyaev 1976, Piran 1978) • Local thermal instability should result in the “limit-cycle” behaviour (e.g. Honma et al. 1992) • However, not seen in high-state BH binaries with LX up to 0.5 LEdd (e.g. Gierliński & Done 2004) except maybe in GRS 1915+105 (Belloni et al. 1997, Xue et al. 2011) • MHD simulations (e.g. Hirose et al. 2009) showed that there are no such thermal instabilities • “Limit-cycle” behaviour not seen in HLX-1 lightcurve Accretion Flow Instabilities 2012 How is the BH fed? (Lasota et al. 2011) • Recurrence timescale = orbital modulation • Modulated mass-transfer from a donor star in an eccentric orbit e ~ 0.7 P ~ 1 yr At periastron, the star fills its Roche lobe and matter falls onto the disk. AGB star C/O AGB stars known to have significant mass loss up to 10-4 MΘ yr-1 (e.g. Bowen & Wilson 1991) Matter will diffuse inwards on a viscous timescale pre-existing disk Accretion Flow Instabilities 2012 How is the BH fed? (Lasota et al. 2011) • Recurrence timescale = orbital modulation • Modulated mass-transfer from a donor star in an eccentric orbit • “Plateaus” seen in the lightcurve around the peak consistent with an enhanced mass-transfer mechanism • Caveat: viscous timescale possibly too long with respect to the recurrence timescale Accretion Flow Instabilities 2012 The nature of the host? (Farrell et al. 2012) • Faint optical counterpart detected in 2010 (Soria et al. 2010) • Swift/UVOT and GALEX (FUV & NUV) images show evidence for extended emission towards the HLX-1 position (Webb et al. 2010) HST --NUV GALEX NUV HST - -FUV GALEX FUV HLX-1 HLX-1 background galaxy (z~0.03) Magellan contours dust lanes • Host: A starburst region (IMBH = run-away collisions & mergers of massive stars – Freitag et al. 2006)? An interaction between an IMBH dwarf galaxy and ESO243-49 producing a trail of stars (e.g. Sun et al. 2010)? • DDT with HST to constrain the nature of the host in 2010 (FUV, NUV, C, V, I, H) – simultaneous observations in X-rays with Swift Accretion Flow Instabilities 2012 The nature of the host? (Farrell et al. 2012) HLX-1 • HLX-1 counterpart detected from FUV to H band. • Optical source is not resolved in any filters. • Host size < 40 pc in diameter Globular clusters have half-mass radius ~ 10 pc (e.g. Harris 1996) Young stellar cluster have half-mass radius < 50 pc (Portegies Zwart et al. 2010) Accretion Flow Instabilities 2012 The nature of the host? (Farrell et al. 2012) • Spectral fitting of the SED (X-rays & optical/NIR) • 2 possible solutions Stellar pop. model (Maraston et al. 2005) Irradiation model diskir (Gierliński et al. 2008, 2009) Γ = 2.1 (fixed) kTcor. = 100keV (fixed) Rout ~ 103.4 Rin kTdisk ~ 0.2 keV Young * pop. Age: Mass: Disc irradiation: 2 (d.o.f.): < 1.3 x 107 yrs 4 x 106 M 8 x 10-7 23.38 (27) Old * pop. 1.3 x 1010 yrs Between 200 Myrs & 10 Gyrs, Irradiation fraction >> 10% 6 x 106 M 0.098 24.28 (27) Accretion Flow Instabilities 2012 The nature of the host? (Farrell et al. 2012) • GCs dominated by old stars in our Galaxy (Forbes 2003) • However, GCs with young stellar pop. observed around disrupted galaxies (e.g. Antennae – Bastian et al. 2006) & Magellanic Clouds (Elson & Fall 1985) • A GC with ~4 x 106 M corresponds to the upper end of standard GC mass range (Maraston et al. 2004). • Alternative: Accreted dwarf galaxy scenario (e.g. Knierman et al. 2010, Mapelli et al. 2012) a large fraction of gas & stars tidally stripped from the dwarf galaxy during interaction leaving only stars most closely bound to the BH (GC-like) star formation triggered by tidal interactions compatible with eccentric binary scenario presence of dust lanes in ESO243-49 could provide evidence for a recent or on-going gas-rich interaction (Shabala et al. 2011) Number density of X-ray sources similar to HLX-1 ~ 10-6 Mpc-3 following this scenario (Mapelli et al. 2012) – HLX-1 distance ~ 100 Mpc Accretion Flow Instabilities 2012 Conclusions • HLX-1 located at a distance of ~100 Mpc is the brightest ULX known. • Probably emitting close to the Eddington limit around the peak. • Properties (spectral state transitions, radio flares) similar to what is seen in stellar-mass BH binaries. • Spectral fitting and observations in X-rays/radio provide a strong support for the presence of an IMBH - Mass range = 6000 - 92000 M • Sub-Eddington radiation-pressure dominated accretion disk with a high (~4x10-4 M yr-1) at the outburst peak. • ~1yr recurrence timescale in the outbursts seen in the X-rays could be interpreted as the result of modulated mass-transfer from an AGB star with an eccentric orbit. • HLX-1 host is likely to be a young stellar cluster that is the remnant of a recent or on-going interaction of an IMBH dwarf galaxy with ESO 24349. Accretion Flow Instabilities 2012 What will come next? • 4x12h ATCA observation in the low/hard state to “test” the BH fundamental plane • EVLA/ATCA observations triggered on the 2012 outburst to further investigate the properties of the radio flares • HST/XMM observations at different outburst epochs to constrain the nature of the stellar population • high-resolution ATCA observations in HI to search for evidence of an interaction between HLX-1 host and ESO 243-49 (tidal tails) • VLT/Swift monitoring campaign to track the rise of the 2012 outburst to constrain the outburst mechanism (inside-out or outside-in) o to test Lasota et al. (2011) binary scenario o to estimate the accretion rate at the outburst peak • Swift-XRT monitoring still on-going