  In relation to the fluctuation-dissipation theorem, we discuss a
time-dependent notion of spectral function and effective temperature. Extending
recent results from arXiv:1212.6066, we work out these quantities in a
two-dimensional thermalising CFT dual to AdS3-Vaidya spacetime which
interpolates between a black brane geometry at early times and a higher
temperature black brane at late times. The computation is carried out in the
gravitational holographic dual in the geodesic approximation and using a
non-standard analytic continuation.
