The extended Unruh effect in the Kruskal spacetime

Originally, the Unruh effect is considered in the Minkowski spacetime. That is, for a uniformly accelerated observer in the Minkowski spacetime, there will be an event horizon, and the observer will detect radiation from it. In this paper, we extend the Unruh effect to the Kruskal spacetime. After defining some special null hypersurface in the Kruskal spacetime, we find that it can be considered as the event horizon for some accelerated observers, too. Moreover, there is radiation from it. In addition, our result shows that these observers by definition are 3-accelerated observers in the Schwarschild space. Thus, the conculsion may be available in the astronomical exploration.