Signatures of massive collisions in debris discs A self-consistent numerical model

Context. Violent stochastic collisional events have been invoked as a possible explanation for some debris discs displaying pronounced azimuthal asymmetries or having a luminosity excess exceeding that expected for systems at collisional steady-state. So far, no thorough modelling of the consequences of such stochastic events has been carried out, mainly because of the extreme numerical challenge of coupling the dynamical and collisional evolution of the released dust. Aims. We perform the first fully self-consistent modelling of the aftermath of massive breakups in debris discs. We follow the collisional and dynamical evolution of dust released after the breakup of a Ceres-sized body at 6 AU from its central star. We investigate the duration, magnitude, and spatial structure of the signature left by such a violent event, as well as its observational detectability. Methods. We use the recently developed LIDT-DD code, which handles the coupled collisional and dynamical evolution of debris discs. The main focus is placed on the complex interplay between destructive collisions, Keplerian dynamics, and radiation pressure forces. We use the GRaTer package to estimate the system's luminosity at different wavelengths. Results. The breakup of a Ceres-sized body at 6AU creates an asymmetric dust disc that is homogenized by the coupled action of collisions and dynamics on a timescale of a few 10(5) years. After a transient period where it is very steep, the particle size distribution in the system relaxes to a collisional steady-state law after similar to 10(4) years. The luminosity excess in the breakup's aftermath should be detectable by mid-IR photometry, from a 30 pc distance, over a period of similar to 10(6) years that exceeds the duration of the asymmetric phase of the disc (a few 10(5) years). As for the asymmetric structures, we derive synthetic images for the VLT/SPHERE and JWST/MIRI instruments, showing that they should be clearly visible and resolved from a 10 pc distance. Images at 1.6 mu m (marginally), 11.4, and 15.5 mu m show the inner disc structures, while 23 mu m images display the outer disc asymmetries.