Dynamical constraints on the mass of the black hole in a ULX No ^ Tim Roberts Jeanette Gladstone (Alberta) Andy Goulding, Mark Swinbank, Martin Ward (Durham) Mike Goad (Leicester) Andrew Levan (Warwick)

Tim Roberts - ULX dynamical masses ULX mass estimates Wide variety of methods used to make indirect measurements of BH mass (e.g. Zampieri & Roberts 2009) X-ray luminosity & spectra Cool discs as IMBHs (e.g. Miller et al. 2003) Disc-dominated spectral models giving MBH ~ 10 – 80 M (e.g. Vierdayanti et al. 2006) Super-Eddington accretion models implying MBH < 100 M (e.g. Gladstone et al. 2009) Weds 26th May 2010 Tim Roberts - ULX dynamical masses

Tim Roberts - ULX dynamical masses ULX mass estimates (2) X-ray timing measurements Scaling QPO, break frequencies gives IMBHs (e.g. Strohmayer & Mushotzky 2009) But lack of variability in some ULXs argues for small BHs (e.g Heil et al. 2009) Optical constraints Counterpart magnitudes & colours (e.g. Patruno & Zampieri 2010) All degenerate, reliant on assumptions Weds 26th May 2010 Tim Roberts - ULX dynamical masses

Dynamical masses: a heritage 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) Weds 26th May 2010 Tim Roberts - ULX dynamical masses

Extragalactic dynamical masses Recently: two X-ray binaries outside our Galaxy with BH dynamical masses M33 X-7 (Orosz et al. 2007) – eclipsing system IC 10 X-1 (Prestwich et al. 2007) – WR-BH binary with MBH ~ 24 – 33 M IC 10 X-1 radial velocity curve (Silverman & Filippenko 2009) Weds 26th May 2010 Tim Roberts - ULX dynamical masses

Problems with doing this for ULXs… Going from ~1 Mpc to several Mpc… Faint counterparts (mv ~ 20.5 at best; typically > 24, Roberts et al. 2008) Confused fields (stars & nebulae) Observational challenge! HST data for Ho II X-1 (Kaaret et al. 2004) Weds 26th May 2010 Tim Roberts - ULX dynamical masses

Tim Roberts - ULX dynamical masses Previous attempts Kaaret & Corbel (2009) – NGC 5408 X-1 6 VLT/FORS observations in 3 days No absorption lines from stellar companion; broad He II (face-on system?) Pakull, Grise et al. – NGC 1313 X-2 Early observations show Δv ~ 380 km s-1 in He II line between epochs (Pakull et al. 2006) Follow-up in 2008/9 – no radial velocity variations(?) Weds 26th May 2010 Tim Roberts - ULX dynamical masses

Towards a ULX dynamical mass We have been developing a programme to attempt to obtain ULX dynamical masses 3-step process: Identify counterparts from Chandra astrometry and HST imaging (Jeanette Gladstone thesis; Gladstone et al. in prep.) Obtain pilot optical spectroscopy observations to identify useful spectral features Undertake the RV measurements campaign Weds 26th May 2010 Tim Roberts - ULX dynamical masses

Best targets Luminous ULXs (> 5 ×1039 erg s-1) NGC 1313 X-2 Ho IX X-1 m555 = 22.5 Weds 26th May 2010 Tim Roberts - ULX dynamical masses

Pilot spectroscopy results Gemini G-MOS spectra obtained B600 grating Gemini-S NGC 1313 X-2, 3 hr Gemini-N NGC 5204 X-1, 0.8 hr Ho IX X-1, 1.5 hr Weds 26th May 2010 Tim Roberts - ULX dynamical masses

New programme on Gemini GN-2009B-Q-21: Ho IX X-1 (18.6 hours) 1.5 hours per observation GS-2009B-Q-20: NGC 1313 X-2 (29.2 hours) 2.5 hours per observation Strategy: request 10 observations performed on nightly intervals (when possible) Liu et al. (2009): ~ 6 day period in NGC 1313 X-2 Madhusudhan et al. (2008): 1 – 10 day periods expected for small BHs in ULXs Weds 26th May 2010 Tim Roberts - ULX dynamical masses

Data obtained NGC 1313 X-2: 1 obs. Oct, 9 in 13 nights Dec 2009 Ho IX X-1: 5 obs. late Dec 2009, 5 obs. Feb 2010. Portion of 2-D spectrum from 26th Dec 2009 observation of Ho IX X-1 Weds 26th May 2010 Tim Roberts - ULX dynamical masses

He II 4686Å shifts relative to nebula Data from Ho IX X-1 Weds 26th May 2010 Tim Roberts - ULX dynamical masses

Periodicity? NOT PERIODIC Best fit: P = 1.73 days, K = 77 km s-1 Reduced χ2 ~ 5 NOT PERIODIC Weds 26th May 2010 Tim Roberts - ULX dynamical masses

Any better luck with NGC 1313 X-2? Weds 26th May 2010 Tim Roberts - ULX dynamical masses

Tim Roberts - ULX dynamical masses No. Best fit P = 3.01 days, K = 61 km s-1 Reduced χ2 ~ 4 Weds 26th May 2010 Tim Roberts - ULX dynamical masses

Is all lost? Ho IX X-1 data No – He II line profile is broad and variable on timescales of days Weds 26th May 2010 Tim Roberts - ULX dynamical masses

Similarly for NGC 1313 X-2 He II line profile broad and highly variable on timescales of days! Weds 26th May 2010 Tim Roberts - ULX dynamical masses

Tim Roberts - ULX dynamical masses Implications He II emission from very close to ULX Solution: accretion disc reprocessing? Broadening implies not completely face-on Line widths consistent with location very far out in disc… …or a small velocity component in line-of-sight If this is from disc, can use limit from scatter in velocity shift to put lower limit on BH mass But other possibility: emission in wind? Weds 26th May 2010 Tim Roberts - ULX dynamical masses

Mass limits NGC 1313 X-2 Ho IX X-1 2σ upper limits: K < 97 km s-1 (Ho IX X-1); K < 182 km s-1 (NGC 1313 X-2) NGC 1313 X-2 6-day photometric period Ho IX X-1 Weds 26th May 2010 Tim Roberts - ULX dynamical masses

Tim Roberts - ULX dynamical masses One more thing… Stack all 15 hrs observations to get high quality optical spectrum Ho IX X-1 looks featureless, very blue - dominated by accretion disc light? Weds 26th May 2010 Tim Roberts - ULX dynamical masses

NGC 1313 X-2: more interesting Continuum less strong in 25 hrs on NGC 1313 X-2 Possible stellar features appearing at short wavelengths? Weds 26th May 2010 Tim Roberts - ULX dynamical masses

Tim Roberts - ULX dynamical masses Conclusions Ambitious programme to constrain the dynamical mass of two ULXs attempted He II line centroid varies; but not periodically Places no strong limit on BH mass He II line is however broad and highly variable on timescales of days Could be from the accretion disc: implying source close to face-on? Or from a wind? Stacked spectra: very different counterparts Weds 26th May 2010 Tim Roberts - ULX dynamical masses