dust echo

A dust echo is the thermal emission of dust heated by a transient event that produces substantial EMR. Typical is some infrared from a region some distance from the transient event after the transient heated the dust with more energetic photons, e.g., X-rays. If the heated dust is a some distance beyond the initial event, then our reception of the dust glow begins later than does the EMR directly from the event, potentially months or years. Even if the dust is close, with the echo occurring nearer in time, the echo can extend the length of time that the transient can be observed: it shows as some infrared during the time that the dust subsequently cools. For transients that produce most of their EMR beamed in a particular direction, the dust echo may be all that we can detect. An example of a transient with an observable dust echo is that of a tidal disruption event (TDE) occurring within a dusty star-forming galaxy.

The term light echo is also used for this phenomenon but is potentially more general, applicable if the echo is due to scattering and/or if no dust is involved.