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Astron. Astrophys. 356, 788-794 (2000)

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5. Conclusions

The X-ray surface brightness around NGC 1275 (dominant galaxy of the Perseus cluster) is perturbed at various spatial scales. We suggest that on arcminute scales, the disturbance is caused by bubbles of relativistic plasma, inflated by jets during the past [FORMULA] years. Overall evolution of the buoyant bubble will resemble the evolution of a hot bubble during a powerful atmospheric explosion. Colder gas from the central region of the cooling flow may be uplifted by the rising bubbles and (in the case of continuous jet activity) may make several cycles (from the center to the outer regions and back) on time scales comparable to the cooling time of the gas in the cooling flow.

A very important result that can be inferred from this model is the total power output of the nuclear energy source in NGC 1275 in the form of relativistic plasma. This energy release averaged over a time scale of about [FORMULA] to [FORMULA] years is estimated as a function of the inflation time of the central radio lobes, the rise time of the inflated bubbles due to buoyancy forces, and the actual size of the central bubbles. A geometrically simplified model yields a power output on the order of [FORMULA] erg s-1. This is comparable with the energy lost at the same time by thermal X-ray radiation from the entire central cooling flow region. This raises the question, where does all this energy go, especially if the energy release is persistent over a longer epoch during which the relativistic electrons can lose their energy by radiation, but the energy in protons and in the magnetic field is mostly conserved. The complicated X-ray morphology discussed in this paper may indicate long lasting nuclear activity, if we interpret the peculiar structure in the X-ray surface brightness as remnants of decaying radio lobe bubbles.

Detailed measurements of the morphology of the X-ray structure and the temperature and abundance distribution with Chandra and XMM may test this hypothesis. The gas uplifted from the central region is expected to be cooler than the ambient gas and to have an abundance of heavy elements typical of the innermost region. If cosmic rays are mixed with the thermal gas, then the pressure, as derived from X-ray observations, may be lower than the pressure of the ambient gas.

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© European Southern Observatory (ESO) 2000

Online publication: April 17, 2000