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arXiv · 1506.02988

The evolution of a jet ejection of the ultraluminous X-ray source Holmberg II X-1

D. Cseh·J. C. A. Miller-Jones·P. G. Jonker·F. Grise·Z. Paragi·S. Corbel·H. Falcke·S. Frey·P. Kaaret·E. Koerding
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Abstract

We present quasi-simultaneous, multi-epoch radio and X-ray measurements of Holmberg II X-1 using the European VLBI Network (EVN), the Karl G. Jansky Very Large Array (VLA), and the Chandra and Swift X-ray telescopes. The X-ray data show apparently hard spectra with steady X-ray luminosities 4 months apart from each other. In the high-resolution EVN radio observations, we have detected an extended milli-arcsecond scale source with unboosted radio emission. The source emits non-thermal, likely optically thin synchrotron emission and its morphology is consistent with a jet ejection. The 9-GHz VLA data show an arcsecond-scale triple structure of Holmberg II X-1 similar to that seen at lower frequencies. However, we find that the central ejection has faded by at least a factor of 7.3 over 1.5 years. We estimate the dynamical age of the ejection to be higher than 2.1 years. We show that such a rapid cooling can be explained with simple adiabatic expansion losses. These properties of Holmberg II X-1 imply that ULX radio bubbles may be inflated by ejecta instead of self-absorbed compact jets.

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D. Cseh, J. C. A. Miller-Jones, P. G. Jonker, F. Grise, Z. Paragi, S. Corbel, H. Falcke, S. Frey, P. Kaaret, E. Koerding. 2015-06-09. The evolution of a jet ejection of the ultraluminous X-ray source Holmberg II X-1. https://arxiv.org/abs/1506.02988

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