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Deriving direct mass measurements of black holes in ULXs

Deriving direct mass measurements of black holes in ULXs. Jeanette Gladstone, T. Roberts, C. Copperwheat, A. Goulding, C. Heinke, A Swinbank, T. Cartwright, A. Levan, M. Goad, M. Ward. And work by others. Importance of mass measurements. All aware of historical aspect.

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Deriving direct mass measurements of black holes in ULXs

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  1. Deriving direct mass measurements of black holes in ULXs Jeanette Gladstone, T. Roberts, C. Copperwheat, A. Goulding, C. Heinke, A Swinbank, T. Cartwright, A. Levan, M. Goad, M. Ward. And work by others

  2. Importance of mass measurements • All aware of historical aspect • Stellar remnant black hole (<~100 Msun)? • Beamed emission (relativistic jets)? (e.g. Körding et al. 2002) • Anisotropic system? (King et al. 2001) • True super-Eddington accretion? • Intermediate mass black holes (IMBHs) • Intermediate in Luminosity between stellar mass & super-massive black holes • The missing link in the mass scale? • Isotropically, sub-Eddington accretion in a standard accretion state

  3. Indirect measurements gave us ... • Lead to sub-classification of ULXs, relating to potential explanations of mass/accretion processes • standard ULXs (sULXs) • ~1039 erg s-1 < LX < ~ 2 * 1040 erg s-1

  4. Indirect measurements gave us ... • Lead to sub-classification of ULXs, relating to potential explanations of mass/accretion processes • standard ULXs (sULXs) • ~1039 erg s-1 < LX < ~ 2 * 1040 erg s-1 • includes the borderline & transients • LX < ~ 3 * 1039 erg s-1

  5. sULXs • majority thought to be stellar remnant black hole approaching or exceeding Eddington • number in interacting galaxies (King 2004) • star-formation association (Swartz et al. 2009) • X-ray spectra (Gladstone et al. 2009; Bachetti et al. 2013) • transient sources showing evolution to ULX like spectra (Middleton et al. 2012; 2013) Composite image - Chandra (purple); Galaxy Evolution Explorer satellite (ultraviolet/blue); HST (visible/green); Spitzer (infrared/red). (NASA/JPL/Caltech/P.Appleton et al. X-ray: NASA/CXC/A.Wolter \& G.Trinchieri et al. Unfolded spectrum of NGC 1313 X-2 containing XMM-Newton & NuSTAR from Bachetti et al. 2013

  6. Indirect measurements gave us ... • Lead to sub-classification of ULXs, relating to potential explanations of mass/accretion processes • standard ULXs (sULXs) • ~1039 erg s-1 < LX < ~ 2 * 1040 erg s-1 • includes the borderline & transients • LX < ~ 3 * 1039 erg s-1 • extreme ULXs (eULXs) • ~2 * 1040 erg s-1 < LX < ~ 1041 erg s-1

  7. eULXs • mix of stellar remnant & IMBHs? • harder spectra • more variability • may be IMBHs, and yet • NGC 5907 ULX show signs of high energy break - similar to sULXs Sutton et al. (2012) Sutton et al. (2013)

  8. Indirect measurements gave us ... • Lead to sub-classification of ULXs, relating to potential explanations of mass/accretion processes • standard ULXs (sULXs) • ~1039 erg s-1 < LX < ~ 2 * 1040 erg s-1 • includes the borderline & transients • LX < ~ 3 * 1039 erg s-1 • extreme ULXs (eULXs) • ~2 * 1040 erg s-1 < LX < ~ 1041 erg s-1 • HLXs • LX > 1041 erg s-1

  9. HLXs • strongest candidates for IMBHs. • few known • Brightest reported ESO 243-49 HLX-1, reaching ~ 1042 erg s-1 Composite HST image of ESO 243-49 constructed from all UV, optical and near-IR WFC3 data, with position of HLX-1 marked

  10. So what is there still to do? • Evidence is indirect, need to confirm this to convince wider community Dynamical mass measurements using the optical companion Start where we have the more information, and most sources ... sULXs

  11. Optical Counterparts • First stage - identify optical counterparts • number of individual sources identified • need bright nearby objects • Gladstone et al. (2013) presented catalogue of of nearby counterparts M81 X-6 NGC 3034 ULX6

  12. Optical counterpart catalogue • combines Hubble & Chandra to identify potential counterparts to ULXs in ~ 5 Mpc • mV ≈ 20-26 • 22 ULX have possible optical counterparts (40 identified; 13 +/- 5 are true) • SED & MV suggest most are OB-type star - one rule this out • X-ray irradiation modelling suggests 10 (of 18) candidate companions are not O stars, while all (18) could be B-type Gladstone et al. (2013) Only a handful bright enough for spectroscopic followup

  13. Pilot spectroscopy • Most spectra appear almost featureless & non-stellar • Nebula lines are present • He II feature visible in some Roberts et al. 2011

  14. Dynamical masses To ‘weigh’ a BH – measure binary period and radial velocity shifts P From companion star: K* From compact object: Early Cyg X-1 data (Bolton 1975) from stellar absorption lines Radial velocity curve of GRO J1655 from He II line (Soria et al. 1998)

  15. Varying He II emission (Ho IX X-1)?

  16. The problem • A deeper look reveals extended He II emission • Single He II line contains 2 components • Currently don’t have the resolution to separate the two • Need next generation if telescope/instruments • We can work with limits however … Ho IX X-1 Moon et al 2011

  17. Current constraints Ho IX X-1 2σ upper limits: K < 97 km s-1

  18. What about more transient souces? • M101 ULX • Distance ~7 Mpc • Peak LX ~ 3 * 1039 erg s-1 • Low state LX ~ 2 * 1037 erg s-1 • X-ray outburst occurs every ~6 months, lasting ~10 - 30 days • Luminosity in high state far exceeds that of other transients • Affords opportunity to study in low state

  19. Optical observations of M101 ULX1 • Observed with Gemini Feb - May 2010, when in low state • Combined spectra confirms secondary is Wolf-Rayet star Text Mass ~ 18Msun Radius ~ 10.7 Rsun

  20. Period? • orbital period of ~8.2 days • K ~ 61 km/s • M ≳ 5 Msun

  21. M101 ULX1 • Average LX ~ 3 * 1038 erg s-1 • Average rate ~ (1/ƞ) 6 * 10-9Msun/yr • By folding in estimates for the average mass accretion rate obtain a likely mass of 20 - 30 Msun • Similar mass range to IC 10 X-1 & NGC 300 X-1

  22. The difficulties in obtaining mass estimates • ULXs are bright in X-rays • Create fascinating systems to observe and investigate • tend to cause problems with He II emission • need the next generation instruments / equipment for study of most systems • can get round this by studying transient systems • seems to show slightly larger stellar remnant black holes • as for other sub-classes, there is still much to do

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