Unveiling recurrent jets of the ULX Holmberg II X-1: evidence for a massive stellar-mass black hole?

Cseh, D. and Kaaret, P. and Corbel, S. and Grisé, F. and Lang, C. and Körding, E. and Falcke, H. and Jonker, P. G. and Miller-Jones, J. C. A. and Farrell, S. and Yang, Y. J. and Paragi, Z. and Frey, Sándor (2014) Unveiling recurrent jets of the ULX Holmberg II X-1: evidence for a massive stellar-mass black hole? MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY: LETTERS, 439 (1). L1-L5. ISSN 1745-3925

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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 syn- chrotron radiation. The central component has a steep radio spectrum and is brighter than the outer components indicating a renewed radio activity. We estimate a min- imum time-averaged jet power of ∼2 × 1039 erg s−1 that is associated with a time- averaged isotropic X-ray luminosity of at least 4 × 1039 erg s−1. Our results suggest that Holmberg II X-1 is powered by a black hole of MBH > 25 M⊙, that is inferred to be accreting at a high Eddington rate with intermittent radio activity.

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