  We measure the correlation spectrum of the Hawking radiation emitted by an
analogue black hole and find it to be thermal at the Hawking temperature
implied by the analogue surface gravity. The Hawking radiation is in the regime
of linear dispersion, in analogy with a real black hole. Furthermore, the
radiation inside of the black hole is seen to be composed of negative-energy
partners only. This work confirms the prediction of Hawking's theory regarding
the value of the Hawking temperature, as well as the thermality of the
spectrum. The thermality of Hawking radiation is the root of the information
paradox. The correlations between the Hawking and partner particles imply that
the analogue black hole has no analogue firewall.
