What are the essential ingredients of ultraluminous X-ray sources?

1. What are the essential ingredients of ultraluminous X-ray sources? Roberto Soria (CfA & MSSL) Some ULX collaborators: M Cropper, C Copperwheat (MSSL), R Fender (Southampton), Z Kuncic, C Hung (Sydney), D Swartz (MSFC), A Goncalves (Paris-M), M Pakull, F Grise’ (Strasbourg), R. Mushotzky (GSFC)

2. What we’d like to know about ULXs • Mass • No direct (kinematic) mass determination yet. • Two or three candidates perhaps feasible now. 2) How to gain a factor of ~ 50 in apparent Lx with respect to stellar-mass BHs Beamed (microblazars?) Higher BH mass (IMBHs?) Not beamed Super-Eddington luminosity

3. Searching for common features in the ULX population “Soft-excess” in their X-ray spectra? Signature of a cool disk? higher BH mass?

4. Holmberg II X-1 (Lx ~ 2E40 erg/s) “soft excess” Power law (G ~ 2) kT ~ 0.15 keV

5. Holmberg II X-1 (Lx ~ 2E40 erg/s)

6. Searching for common features in the ULX population “Soft-excess” in their X-ray spectra? Signature of a cool disk? higher BH mass? Most bright ULXs (Lx ~ 1E40 erg/s) have it (Stobbart et al 06) A few do not, pure power-law spectrum (Winter et al 06) Evidence of IMBHs, M ~ 1000 Msun ?

7. “Soft-excess” interpretation is still unclear See also poster by Soria, Goncalves & Kuncic Cool disk emission Smeared absorption lines in fast, ionized outflow

8. Holmberg II X-1 (Lx ~ 2E40 erg/s) Power law (G ~ 2.5)

9. Holmberg II X-1 (Lx ~ 2E40 erg/s)

10. Injected spectrum (power-law) Emerging spectra with absorption from ionized, fast-moving outflow (v ~ 0.1 c, nH ~ 3E22) Models by Goncalves et al. References: Gierlinski & Done (2004) Crummy et al (2006) Goncalves & Soria (2006)

11. “Soft-excess” interpretation is still unclear See also poster by Soria, Goncalves & Kuncic Standard disk around IMBH Cool disk emission Non-standard disk Smeared absorption lines in fast, ionized outflow More generally: absorption + re-emission + reflection

12. Essential feature of X-ray spectra: Dominated by non-thermal emission Disk radiates only ~ 10-20% of output accretion power Most power is efficiently transferred from disk to upscattering medium (jet/corona) Disk should be cooler than a standard SS disk for a given BH mass

13. Chilled disk Cooler than standard disk because power is drained from disk into jet+wind+corona see also Z. Kuncic’s talk

14. Chilled disk Cooler than standard disk because power is drained from disk into jet+wind+corona see also Z. Kuncic’s talk (Soria & Kuncic, in prep.)

15. Searching for common features in the ULX population Jets, outflows? Radio cores: not detectable yet (< 0.1 mJy) Resolved jets: not detectable yet Radio lobes: likely detection in a few sources Energy in lobes >~ 1E52 erg Size ~ 50-70 pc Typical fluxes ~ 0.1-0.2 mJy at 5 GHz

16. Radio lobes of a ULX in NGC 5408 (Soria, Fender et al 2006) Subaru B + ATCA 5 GHz CFHT Ha + ATCA 5 GHz

17. Searching for common features in the ULX population Jets, outflows? Radio cores: not detectable yet (< 0.1 mJy) Resolved jets: not detectable yet Radio lobes: likely detection in a few sources Optical nebulae: observed in many bright ULXs sizes ~ 50-400 pc X-ray photoionized or collisionally ionized?

18. HST/ACS Optical nebulae Jet lobes? NGC 1313 X-2 (Pakull, Grise & Motch 2006) ULX Hot spot? (hot ring?) Star 30 pc MF16 “SNR” + ULX, in NGC 6946 (Swartz et al 2006, in prep) = 80 pc

19. Searching for common features in the ULX population Jets, outflows? Likely to be essential ingredient but more evidence needed

20. Searching for common features in the ULX population Young host environment? Not essential for fainter ULXs (Lx <~ 3E39 erg/s) Essential for brighter ULXs (Lx >~ 1E40 erg/s) Only found in spiral & irregular galaxies “Young” = less than 50 Myr Donor = OB star transferring gas on its nuclear timescale

21. Searching for common features in the ULX population Starburst environment? Some ULXs are in starburst galaxies (eg, Cartwheel, Antennae, Mice) Some are in very quiet corners of nuclear starburst or starforming galaxies (eg, NGC 7714, M83, M99) Some are in tidal dwarfs with little star formation (eg, Ho II, Ho IX) NOT AN ESSENTIAL INGREDIENT but some association

22. Searching for common features in the ULX population Super star-clusters? Suggested as site of IMBH formation via O-star coalescence (Portegies Zwart et al; Rasio et al) But inconsistent with ULX observations (except for M82 X-1) Most ULXs found in OB associations or open clusters, with masses <~ a few 1000 Msun NOT AN ESSENTIAL INGREDIENT

23. Searching for common features in the ULX population Colliding or tidally interacting systems? Galaxy-galaxy collisions (eg, ULXs in Antennae, Mice, Cartwheel, NGC 4485/90, NGC 7714/15) Satellite dwarf – galaxy collisions (eg ULX in NGC 4559) HI cloud – disk collisions (eg ULX in M99) Tidal dwarfs and tails (eg ULXs in Ho II, Ho IX)

24. Searching for common features in the ULX population Colliding or tidally interacting systems? Essential or very important ingredient

25. The Antennae Examples of ULXs formed in colliding events NGC 4559

26. M99 (Soria & Wong 2006) XMM EPIC image (0.2-12 keV) HI contours over R image LX ~ 2 1040 erg/s (see poster by Soria & Wong)

27. High-velocity cloud collision with M99 gas disk Only a coincidence?

28. Searching for common features in the ULX population Low-metallicity environment? Mounting evidence but no systematic study yet (eg, ULXs in Cartwheel, Ho II, NGC 4559, NGC 5408, 1 Zw 18) More massive BH remnants expected from metal-poor O stars (Mwind ~ Z0.5-0.8) . Probably a very important ingredient

29. My (biased) conclusions: I: NATURE OF (MOST) ULXs Simplest model still consistent with the data: BH masses ~ 30 – 100 Msun (upper limit of stellar processes) Age of the accreting systems < 50 Myr (OB donor)

30. II: (SPECULATIVE) FORMATION PROCESS Triggered star formation(eg, ram p from cloud/galaxy collisions) Dynamical collapse of molecular clumps (as opposed to turbulent fragmentation) Fast gas accretion and protostellar mergers in a dense protocluster core (clump mass ~ a few 1000 Msun, much smaller than a super cluster) Massive stellar progenitor, Mstar ~ 200 Msun if metal abundance is low BH with a mass ~ 50-100 Msun

31. Externally-triggered dynamical collapse of a molecular clump in the Milky Way Total mass ~ 1700 Msun Infall rate ~ 10-3 Msun/yr Infall timescale ~ 1.7 105 yr CMM3 has 40 Msun, still accreting & merging 35 Msun 40 Msun 15 Msun Peretto et al. (2006)

32. Very massive stars from clustered star formation exist in the Milky Way & LMC: Pistol star: initial mass ~ 200 Msun (but too metal rich to collapse into a BH) R145 in 30 Dor: M sin3i= (140 +/- 37) Msun

33. III. POWER BUDGET Accretion rate up to ~ 10 times Eddington Luminosity near or a few times Eddington Disk radiates only < 20% of the output power Disks are cooler than standard SS Kin. power available for outflows and jets Can BHs have steady jets when accreting at or above Eddington? ULXs could be test cases for QSO super-Edd accretion and feedback models at high redshift

34. A finis si’. Mersi’ che i l’eve scota’.

35. Black hole masses in ULXs Optical counterparts too faint for direct mass-function determinations X-ray Luminosity function cuts off at ~ 3 x 1040 erg/s Eddington limit suggests M ~ 30 - 200 Msun Higher masses (~ 103Msun) speculated from X-ray timing and spectral studies

36. BH mass from X-ray spectral models Galactic X-ray binaries generally show: power-law component + thermal disk component Flatter (G ~ 1.5) when LX <~ 0.01 LEdd Steeper (G ~ 2.5) when LX ~ LEdd 4 4 LX ~ Tin R2 ~ Tin M2 - 4 Lmax ~ LEdd ~ M ~ Tin

37. X-ray spectrum of NGC4559 X7 (XMM) Power-law (G~ 2.3) Tbb ~ 0.12 keV

38. X-ray spectrum of NGC4559 X7 (XMM)

39. G ~ 2.0 Disk kTin ~ 0.13 keV

40. Disk kTin ~ 1.9 keV kTphot ~ 0.27 keV

41. LX (erg/s) 1042 1041 Lx = LEdd Hot-disk model 1000 Msun 1040 1039 15 Msun IMBH model GBHs 1038 5 Msun Tin 0.1 1 0.2 2 (keV)

42. IMBH model Miller, Fabian & Miller (2004) Feng & Kaaret (2005) kTin ~ 0.12 – 0.15 keV M >~ 1000 Msun LX ~ 0.05 – 0.2 LEdd Hot-disk model Stobbart, Roberts & Wilms (2006) kTin ~ 1.5 – 2.5 keV M <~ 10 Msun LX ~ 10 LEdd

43. PROBLEMS: IMBH model similar to NLSy1 kTin ~ 0.12 – 0.15 keV M >~ 1000 Msun LX ~ 0.05 – 0.2 LEdd requires exotic formation processes why do they never reach LEdd? Hot-disk model kTin ~ 1.5 – 2.5 keV M <~ 10 Msun LX ~ 10 LEdd

44. PROBLEMS: IMBH model similar to NLSy1 kTin ~ 0.12 – 0.15 keV M >~ 1000 Msun LX ~ 0.05 – 0.2 LEdd requires exotic formation processes why do they never reach LEdd? Hot-disk model kTin ~ 1.5 – 2.5 keV M <~ 10 Msun LX ~ 10 LEdd ad hoc (esp. ~ 10 keV) standard SS disk should not survive at 10 LEdd !

45. Alternative model: broad absorption G ~ 2.8

47. Summary I Unwise to estimate BH masses from X-ray spectra “Soft excess” may be due to absorption New spectral state? (for ULXs and NLSy1?) . Steep pl + absorption in fast, dense outflow M Very high (steep pl) High/soft (disk) Low/hard (flat pl)

48. ULX radio counterparts: proof of IMBHs? “fundamental plane” of BH activity (Merloni, Heinz & DiMatteo 2004; Fender et al 2004)

49. Few ULXs have a radio counterpart M82 (Kording et al 2005) Holmberg II (Miller, Mushotzky & Neff 2005) NGC 5408 (Kaaret et al 2003; Soria, Fender et al 2006) NGC 7424 (Soria, Kuncic et al 2006) NGC 6946 (Swartz et al 2006, in prep)

50. NGC 5408 (zoomed in) Coincidence between: X-ray (~1E40 erg/s) Radio (~ 0.3 mJy at 5 GHz) Ha(~1E36 erg/s)