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Optical counterparts to Ultraluminous X-ray sources

Optical counterparts to Ultraluminous X-ray sources. Jeanette Gladstone - University of Alberta T. P. Roberts (U of Durham), A. D. Goulding (CfA) T. Cartwright & C. O. Heinke, (U of A), C. Copperwheat & A. J. Levan (U of Warwick), M. R. Goad (U of Leceister).

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Optical counterparts to Ultraluminous X-ray sources

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  1. Optical counterparts to Ultraluminous X-ray sources Jeanette Gladstone - University of Alberta T. P. Roberts (U of Durham), A. D. Goulding (CfA) T. Cartwright & C. O. Heinke, (U of A), C. Copperwheat & A. J. Levan (U of Warwick), M. R. Goad (U of Leceister)

  2. What are Ultraluminous X-ray sources? • X-ray point source residing outside the nucleus of the galaxy • Thought to be X-ray binaries, containing black hole • LX > 1039 erg s-1 (above Eddington limit for 10 solar mass black hole) We know they contain black holes but, what are their masses? What option do we have to explain their nature? Why do we care? composite X-ray (red)/optical (blue & white) image of the spiral galaxy M74 (NASA/CXC/U. Michigan/J. Liu et al.) Jeanette Gladstone

  3. What are ULXs? Why do we care? Intermediate mass black holes Stellar mass black holes Contain objects we can easily form Some of the most extreme accretors in our universe Provides a need for new accretion physics • Missing link in the mass scale • Provide route to form super-massive black holes • Provide insight into the formation of galaxies After more than 30 years of study, we are currently unable to settle this in the X-ray band … how about optical? Either way, we have something different and new to study Jeanette Gladstone

  4. Can use unprecedented spatial resolution of the Chandra telescope Allows for more accurate positioning of sources Also need help of HST From Zampier et al 2004 showing 90% confidence radii for various X-ray instruments against and ESO 3.6m R-band image of NGC 1313 X-2 Identification of optical counterparts Jeanette Gladstone

  5. New search for stellar counterparts • Search restricted <5 Mpc • Total of 45 ULXs • 31 have both archival Chandra & HST data • 23 have potential optical counterparts Gladstone et al in prep M81 X-6 NGC 3034 ULX6 Jeanette Gladstone

  6. Optical counterparts - one stage further • 38 potential counterparts, some are multiple • As data is archival, we have 1-5 bands for each • Magnitudes from available bands can be used to get first order estimate on stellar types NGC 1313 X-1 IC342 X-1 Jeanette Gladstone

  7. Stellar types? • Reveals many are consistent with OB type stars (although some appear later- M, K & G type) • Absolute magnitudes more indicative of giant stars Need to account for X-ray irradiation effects, due to high levels of X-ray emitted from these sources. Jeanette Gladstone

  8. Accounting for an accretion disc • Apply irradiation models to binary systems containing a black hole and a companion star • Black holes cover stellar and intermediate mass range 1000 M • Covers a range of stellar masses and radii • Multiple bands required so only able to apply to ~20 possible counterparts Jeanette Gladstone

  9. cos (i) = 0 Current data cannot provide us with enough information to differentiate We need multiple bands in the same epoch & deeper images to improve statistics NGC 253 ULX2 cos (i) = 0.5 Case 1: 8 < M* < 20 M , very large radius, MBH > 40M Case 2: M* < 20 M , 8 < R* < 80 R, MBH – no constraint Jeanette Gladstone

  10. Another reason for constructing a catalogue … • Secondary aim of this catalogue was to search for optical counterparts that are bright enough to allow for optical spectroscopic follow-up • Highlighted several good sources for follow-up Jeanette Gladstone

  11. Pilot spectra of the ULX counterparts • Gemini G-MOS spectra obtained • Gemini-S • NGC 1313 X-2, 3 hr • Gemini-N • NGC 5204 X-1, 0.8 hr • Ho IX X-1, 1.5 hr Jeanette Gladstone

  12. Varying He II emission? Jeanette Gladstone

  13. Slight complication … 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 We can work with limits however … Ho IX X-1 Moon et al 2011 Jeanette Gladstone

  14. Constraining the mass? Ho IX X-1 2σ upper limits: K < 97 km s-1 Jeanette Gladstone

  15. What are ULXs? • Cannot answer this as yet, do have lower limits • need photometry at multiple wavebands (and spectra) to help classify counterpart • Need greater signal-to-noise and/or resolution to start to statistically separate the He II components • Confirmed 12 possible, identified 26 new potential candidates • Many consistent with OB classification (although some later giants also identified) • By accounting for X-ray irradiation, we are beginning to constrain their mass and radius What about their companions? Jeanette Gladstone

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