tokens: 43 , otherwise the matter is swallowed by the BHs before the merger. The bounding energy of this matter is only a fraction of the rest mass energy of the matter, This ratio is much smaller than the wind efficiency w 0.1 of a super-Eddington accretion disc, so that such matter is easily blown away by the disc wind. As long as a possible dead disc is ionized by the ISM accretion (that occurs unless we consider low n and high v ), we have encountered an unlikely set-up. Note that a fraction of the matter M m should accrete on to the BHs before the merger, otherwise a fine-tuning is needed because the time t b is much larger than the event duration t acc . The accretion is super-Eddington, even if only a fraction of the matter accretes, and should be accompanied by a strong disc wind as suggested by numerical simulations (Ohsuga etal. 2005 ; Jiang, Stone Davis 2014 ; Sadowski etal. 2014 ). Therefore, it is difficult to keep the matter near the BH before the merger and the BH mergers unlikely accompany observable prompt electromagnetic counterparts. 7 SUMMARY AND DISCUSSIONS We suggest possible connections between the BH mergers observed by GWs and the high-energy sources of TeVPeV particles in our Galaxy. The GW observations give a lower limit on the number of merged and hence highly spinning BHs as , and the spinning BHs produce relativistic jets by accreting matter and magnetic fields from the ISM. We calculate the luminosity function, the total power and the maximum acceleration energy of the BH jets, and find that the BH jets are eligible for PeVatrons, sources of CR positrons and TeV unIDs. The BH jets form extended nebulae-like PWNe. If they are observed as TeV unIDs, additional 300 nebulae will be discovered by CTA. We quantify the uncertainties of the estimate for the total power of the BH jets within a factor of 10 3 , which is much better than before the GW detections, by considering the initial BH spin, the velocity distribution depending on the formation scenario, the accretion profile changed by the wind and the feedback by the outflow (Table 2 ). The uncertainties will be reduced by the GW observations, in particular, of the BH spins. It is also important to clarify the feedback by the wind from the sub-Eddington accretion disc on the BondiHoyle accretion. Our considerations on the BH accretion and jet imply that the electromagnetic counterparts to BH mergers including the Fermi GBM event after GW150914 are difficult to detect with the current sensitivity. The accretion from the ISM can evaporate the cold neutral dead disc around the BH. A slight accretion before the merger can also blow away the surrounding matter if any. These should be considered as constraints on dead disc models for prompt electromagnetic counterparts of the BHBH merger. Although we do not go into detail in this paper, there are several sites of particle acceleration for a BH jet. First, the BH magnetosphere acts as a particle accelerator like pulsars if a gap
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