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 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 ★ Stellar remnant black hole (<~100 M sun )? ★ Beamed emission (relativistic jets)? ( e.g. Körding et al. 2002) ★ Anisotropic system? (King et al. 2001) ★ True super- Eddington accretion? ★ Stellar remnant black hole (<~100 M sun )? ★ 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 ★ 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

Indirect measurements gave us... ★ Lead to sub-classification of ULXs, relating to potential explanations of mass/accretion processes ★ standard ULXs (sULXs) ★ ~10 39 erg s -1 < L X < ~ 2 * erg s -1 ★ Lead to sub-classification of ULXs, relating to potential explanations of mass/accretion processes ★ standard ULXs (sULXs) ★ ~10 39 erg s -1 < L X < ~ 2 * erg s -1

Indirect measurements gave us... ★ Lead to sub-classification of ULXs, relating to potential explanations of mass/accretion processes ★ standard ULXs (sULXs) ★ ~10 39 erg s -1 < L X < ~ 2 * erg s -1 ★ includes the borderline & transients ★ L X < ~ 3 * erg s -1 ★ Lead to sub-classification of ULXs, relating to potential explanations of mass/accretion processes ★ standard ULXs (sULXs) ★ ~10 39 erg s -1 < L X < ~ 2 * erg s -1 ★ includes the borderline & transients ★ L X < ~ 3 * erg s -1

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) ★ 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

Indirect measurements gave us... ★ Lead to sub-classification of ULXs, relating to potential explanations of mass/accretion processes ★ standard ULXs (sULXs) ★ ~10 39 erg s -1 < L X < ~ 2 * erg s -1 ★ includes the borderline & transients ★ L X < ~ 3 * erg s -1 ★ extreme ULXs (eULXs) ★ ~2 * erg s -1 < L X < ~ erg s -1 ★ Lead to sub-classification of ULXs, relating to potential explanations of mass/accretion processes ★ standard ULXs (sULXs) ★ ~10 39 erg s -1 < L X < ~ 2 * erg s -1 ★ includes the borderline & transients ★ L X < ~ 3 * erg s -1 ★ extreme ULXs (eULXs) ★ ~2 * erg s -1 < L X < ~ erg s -1

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 ★ 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)

Indirect measurements gave us... ★ Lead to sub-classification of ULXs, relating to potential explanations of mass/accretion processes ★ standard ULXs (sULXs) ★ ~10 39 erg s -1 < L X < ~ 2 * erg s -1 ★ includes the borderline & transients ★ L X < ~ 3 * erg s -1 ★ extreme ULXs (eULXs) ★ ~2 * erg s -1 < L X < ~ erg s -1 ★ HLXs ★ L X > erg s -1 ★ Lead to sub-classification of ULXs, relating to potential explanations of mass/accretion processes ★ standard ULXs (sULXs) ★ ~10 39 erg s -1 < L X < ~ 2 * erg s -1 ★ includes the borderline & transients ★ L X < ~ 3 * erg s -1 ★ extreme ULXs (eULXs) ★ ~2 * erg s -1 < L X < ~ erg s -1 ★ HLXs ★ L X > erg s -1

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

So what is there still to do? Evidence is indirect, need to confirm this to convince wider community 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

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

Optical counterpart catalogue ★ combines Hubble & Chandra to identify potential counterparts to ULXs in ~ 5 Mpc ★ m V ≈ ★ 22 ULX have possible optical counterparts (40 identified; 13 +/- 5 are true) ★ SED & M V 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 ★ combines Hubble & Chandra to identify potential counterparts to ULXs in ~ 5 Mpc ★ m V ≈ ★ 22 ULX have possible optical counterparts (40 identified; 13 +/- 5 are true) ★ SED & M V 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

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

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

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

Periodicity (Ho IX X-1)? No... but

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 … ★ 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

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

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

Optical observations of M101 ULX1 ★ Observed with Gemini Feb - May 2010, when in low state ★ Combined spectra confirms secondary is Wolf-Rayet star ★ Observed with Gemini Feb - May 2010, when in low state ★ Combined spectra confirms secondary is Wolf-Rayet star Text Mass ~ 18 M sun Radius ~ 10.7 R sun

Period? ★ orbital period of ~8.2 days ★ K ~ 61 km/s ★ M ≳ 5 M sun ★ orbital period of ~8.2 days ★ K ~ 61 km/s ★ M ≳ 5 M sun

M101 ULX1 ★ Average L X ~ 3 * erg s -1 ★ Average rate ~ (1/ ƞ ) 6 * M sun /yr ★ By folding in estimates for the average mass accretion rate obtain a likely mass of M sun ★ Similar mass range to IC 10 X-1 & NGC 300 X-1 ★ Average L X ~ 3 * erg s -1 ★ Average rate ~ (1/ ƞ ) 6 * M sun /yr ★ By folding in estimates for the average mass accretion rate obtain a likely mass of M sun ★ Similar mass range to IC 10 X-1 & NGC 300 X-1

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 ★ 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