1)when hawking first propounded this thermal radiation, he took into acount the the gravitational cllapse. so I am not sure, if we consider a stationary system, then there won't be any particle creation. Is this the case? because I think there will not be any mixing of posive and negative frequencies. 2)From Unruh effect, we can also get the temperature.the freely-falling observer and the static observer on the event horizon will have different definition of vacuum, then the temperature can be deduced from the Bogolubov coefficients. But I cann't see why the event horizon is so significant in this case? what happen on the event horizon exactly, when we consider Hawking radiation?