Unveiling recurrent jets of the ULX Holmberg II X-1: evidence for a massive stellar-mass black hole?
Abstract
We report on the discovery of an apparent triple radio structure hidden inside the radio bubble of the ultraluminous X-ray source Holmberg II X-1. The morphology is consistent with a collimated jet structure, which is observed to emit optically thin synchrotron radiation. The central component has a steep radio spectrum and is brighter than the outer components indicating a renewed radio activity. We estimate a minimum time-averaged jet power of ∼2 × 10^{39} erg s^{-1} that is associated with a time-averaged isotropic X-ray luminosity of at least 4×10^{39} erg s^{-1}. Our results suggest that Holmberg II X-1 is powered by a black hole of M_{BH}≥25 M_{⊙}, that is inferred to be accreting at a high Eddington rate with intermittent radio activity. Our results strengthen the view that physical properties of accretion and ejection are scale invariant over a possibly homogeneously populated BH mass range. Future studies may confirm a distinct formation channel of massive stellar-mass BHs, that are possibly caught for a short active time and evolve fast in environments akin to early cosmological conditions.
- Publication:
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The X-ray Universe 2014
- Pub Date:
- July 2014
- Bibcode:
- 2014xru..confE.240C