Schedule Feb 07, 2006
ULX Bubbles: Energetic Hypernova Remnants or Jet Inflated Nebulae ? [Oral Contribution]
Manfred Pakull (France)

An interesting result from the optical study of ultraluminous (i.e. L_x 10^39.5 erg/s) variable X-ray sources in nearby galaxies has been the discovery of huge (several hundred pc diameter (!)) bubble-like emission nebulae surrounding these objects. From the measured line widths (corresponding to ~ 100 km/s) and diagnostic emission-line ratios (e.g. [OI]6300/H_alpha > 0.3) we find that these ULX bubbles are young (<10**6 yrs), largely shock-excited structures, although there is also evidence for contribution from (X-ray) photoionisation close to the sources. Using SUBARU, ESO-VLT and HST photometry of the recently identified underlying poor star clusters to which the ULXs belong, stellar isochrones yield cluster ages of some 20--60 Myrs proving that the stellar population is much older than the ULX bubbles.Straightforward application of adiabatic SNR or wind-bubble dynamics, plus an estimate of the interstellar density from the observed recombination line luminosity of radiative shocks, yields ULX bubble energies of some 10^53 erg. This is much larger than the kinetic energy of a single SNR, and more than the superbubble history from the cluster could have possibly provided during its entire lifetime, let alone during the past 10^6 yrs.Taking into account the effects of a clumpy, rather than uniform ISM and of expansion of the shocks into previously excavated stellar wind bubbles, the energy requirements could be lessened by a factor of ten. This is still much higher than the 10^51 erg kinetic energy of a SN explosion, but is comparable to what has been claimed for \"hypernova\" remnants. However, inspired by the properties of the famous SS433/W50 system and the largely \"dark jets\" from galactic black hole binaries, I will present evidence for ongoing inflation of ULX bubbles by relativistic jets emanating from the presumed accreting black holes in ULXs.Finally, our optical search for nebula around ULXs that are currently X-ray inactive, or that are possibly beamed away from our line-of-sight, has revealed at least one very large (> 200 pc diameter) [OI]6300 bright, i.e. shock-excited, nebula in the nearby spiral NGC~1313. We will discuss these results in the light of current knowledge of past and ongoing energetic input of black-hole binaries into the ISM.

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