1. Evidence for Intermediate Mass Black Holes The Case of ESO 243-49 HLX-1 Sean Farrell | Sydney Institute for Astronomy (SIfA), The University of Sydney, Australia In collaboration with: Natalie Webb (IRAP) | Didier Barret (IRAP) | Mathieu Servillat (CfA) | Olivier Godet (IRAP)

2. The Case of ESO 243-49 HLX-1 ›The discovery of ESO 243-49 HLX-1 ›Confirming the redshift with the VLT ›X-ray variability with XMM-Newton, Chandra & Swift ›Radio observations with the Australian Telescope Compact Array ›The UV/optical/near-IR counterpart with Hubble ›Summary & conclusions 2 Outline:

3. The Case of ESO 243-49 HLX-1 ›HLX-1 discovered coincident with edge-on spiral galaxy ESO 243-49 (Farrell et al. 2009) ›At galaxy distance of ~100 Mpc, max. unabsorbed 0.2 – 10 keV L x = 1.1 x 10 42 erg s -1 ›Previous record held by ULX in Cartwheel galaxy: L x ~ 10 41 erg s -1 (e.g. Gao et al. 2003) ›Large-scale variability with possible spectral state changes observed, ruling out multiple sources (Godet et al. 2009) 3 VLT R-band image of the galaxy ESO 243-49 with the position of HLX-1 indicated by the white circle (Farrell et al., 2009, Nature, 460, 73) Discovery of the Brightest ULX HLX-1

4. The Case of ESO 243-49 HLX-1 ›Faint (R~24 mag) optical counterpart detected within Chandra error circle (Soria et al. 2010) ›Follow-up spectroscopy with VLT detected Hα in emission at redshift consistent with host galaxy (Wiersema et al. 2010) 4 Above: VLT I-band images of ESO 243-49 before (top) and after (bottom) subtraction of the diffuse galaxy light. Right: FORS2 spectra, red = HLX-1, blue = background, black = bkg subtracted Confirming the redshift

5. The Case of ESO 243-49 HLX-1 ›Significant variability by a factor of ~50 observed ›Light curve follows Fast Rise Exponential Decay (FRED) profile ›Timescale incompatible with thermal-viscous disc instability model ›Radiation-pressure disc instability may be possible (physics still controversial; Hirose et al. 2009a,b ) ›Modulated mass-transfer due to tidal stripping of companion star in eccentric orbit more likely (Lasota et al. 2011) 5 Swift X-ray Telescope (XRT) Light Curve of HLX-1 Godet et al. 2009; Lasota et al. (2011); Servillat et al. (2011) X-ray variability ~380 d?~380 d

6. The Case of ESO 243-49 HLX-1 6 Belloni (2010)Servillat et al. (2011) ~0.03L ED ~0.8L ED ~1.0L ED L ED ~ 1.1 x 10 42 erg s -1, M BH ~ 8,500 M  See Poster B25 by Mathieu Servillat

7. The Case of ESO 243-49 HLX-1 ›HLX-1 observe to transition between high/soft, soft intermediate, and low/hard states ›Temperature varies as L disc ~ T 4, consistent with geometrically thin optically thick disc ›Fitting thermally dominated spectra with relativistic models (BHSPEC, KERRBB, KERRDISK) constrains mass to ~10 3 < M BH < 10 5 M  (Davis et al. 2011; Godet et al. 2011) 7 X-ray spectral state transitions of HLX-1 Thermal plasma contribution from host galaxy nucleus Servillat et al. (2011)

8. The Case of ESO 243-49 HLX-1 8 Athena vs XMM-Newton

9. The Case of ESO 243-49 HLX-1 ›Observed HLX-1 with ATCA following transition from low/hard to high/soft state ›Detected 40 μJy point source at X-ray position (4.2σ when compared to background flux; Webb et al. 2011 ) ›Follow-up observation ~3 months later failed to detect radio emission ›Variability rules out radio nebula ›Radio emission most likely associated with jet-ejection event ›Using fundamental plane relation (e.g. Fender et al. 2009), mass constrained to < 10 5 M  9 13-09-10 04-12-10 See Poster B30 by Natalie Webb Webb et al. (2011)

10. FUVNUVC VI H H The Case of ESO 243-49 HLX-1 10 HST Imaging of HLX-1 In Sept 2010 we obtained HST observations of HLX-1 in 6 bands (Farrell et al. in prep)

11. 11 Composite 6-band HST image (Farrell et al. 2011, in prep) HLX-1 The Case of ESO 243-49 HLX-1

12. UVOT uvw2 12 Bkg galaxies HST Near-UV Why Hubble is necessary… HST Far-UV The Case of ESO 243-49 HLX-1 Hα VLT FORS2 2-D spectrum

13. Wavelength (Å) F λ (photons/cm 2 /s/Å) The Case of ESO 243-49 HLX-1 ›Fitted HST data with Maraston (2005) simple stellar population models ›X-ray spectrum indicates contribution from accretion disc, so treat UV points as upper limits ›Age, Z, and Av are degenerate, but SED most consistent with young population ›Ages >>100 Myr not consistent with SED 13 HST SED fitted with stellar population models Farrell et al. (2011)

14. The Case of ESO 243-49 HLX-1 14 Broad-band Spectral Energy Distribution Fitting ›X-ray & UV bands described by irradiated disc model ›Red optical & H-band data not consistent  need stellar population ›Disc temp consistent with ~10,000 M  black hole ›FUV luminosity of 7 x 10 39 erg s -1 inconsistent with beamed emission from stellar mass black hole Farrell et al. (2011) Stellar population X-ray NIR/optical/UV

15. The Case of ESO 243-49 HLX-1 ›X-ray luminosity of HLX-1 varies from ~10 – 400 times Eddington limit of 20 M  black hole ›Spectral hysteresis observed very similar to Galactic black hole binaries ›Transient radio emission from jet ejection event  first detection of jets from a ULX ›Mass estimates from Eddington scaling, accretion disc continuum fitting, and jet flare luminosity all support M BH ~ 10 4 M  ›Broad-band SED fitting indicates disc emission dominates X-ray & UV bands, with young stellar population accounting for redder emission ›UV disc luminosity and disc irradiation rule out beaming ›Derived stellar ages inconsistent with globular cluster, instead implying HLX-1 could be nucleus of stripped dwarf galaxy accreted by ESO 243-49 15 Summary & Conclusions:

16. The Case of ESO 243-49 HLX-1 ›Natalie Webb, Didier Barret, Olivier Godet, Dacheng Lin (IRAP, France) ›Jean-Pierre Lasota (IAP, France/Jagiellonian University, Poland) ›Guillaume Dubus (IPAG, France/IAP, France) ›Mathieu Servillat, Ramesh Narayan, Yucong Zhu (Harvard-Smithsonian CfA, USA) ›Neil Gehrels (NASA GSFC, USA) ›Shane Davis (CITA, Canada) ›Tom Maccarone, Christian Knigge (University of Southampton, UK) ›Klaas Wiersema (University of Leicester, UK) ›Claudia Maraston, Janine Pforr (Portsmouth University, UK) ›Andrew Gosling, Ian Heywood (Oxford University, UK) ›Samantha Oates (MSSL, UK) ›Tal Alexander (Weismann Institute of Science, Israel) ›Emil Lenc (CSIRO Astronomy & Space Science, Australia) 16 Thank you to all my collaborators:

17. L vs T disk of a sample of ULXs from Kajava & Poutanen (2009) The Case of ESO 243-49 HLX-1 17 The Soft Thermal Excess in ULX Spectra For Shakura-Sunyaev α-discs: L disk ~ T in 4 However, for most ULXs: L disk ~ T in -3.5 Soft component for bulk of ULXs most likely from outflow such as disc-wind HLX-1 soft excess varies as predicted for an α-disc Servillat et al. (2011)

18. The Case of ESO 243-49 HLX-1 ›Black hole binaries emit radio flares during transition from L/H  H/S (e.g. Fender et al. 2009) ›Flare radio emission can be ~10 times non-flare luminosity ›Applying same scaling to HLX-1 gives M ~10 4 M , ›Radio detection gives conservative upper limit of 10 5 M  18 The Black Hole Fundamental Plane HLX-1 10 6 M sun 10 1 M sun 10 2 M sun 10 3 M sun 10 4 M sun 10 5 M sun HLX-1 HLX-1? HLX-1 Adapted from Merloni et al. (2003)

19. 19 Composite 6-band HST image (Farrell et al. 2011, in prep) HLX-1 The Case of ESO 243-49 HLX-1