Burst particle creation in gravitational collapse to a horizonless compact object

Abstract: In the previous paper [Harada, Cardoso, and Miyata, Phys.\ Rev.\ D {\bf 99} (2019), 044039], it is shown that a hollow transmissive shell collapsing to an ultracompact object of radius very close to its horizon radius generally emits transient Hawking radiation followed by a couple of bursts separated each other by a long time interval. In the current paper, we expand the previous work in two independent directions: changing boundary conditions and specifying the equations of state of the matter. First, we introduce a perfectly reflective surface collapsing to an ultracompact object and find that this model also emits transient Hawking radiation that is followed only by a single burst. Second, we introduce two different collapse dynamics to an ultracompact object and specify the corresponding matter equations of state. We find that transient Hawking radiation is quite commonly seen in early times, while the subsequent bursts strongly depend on the boundary condition and the equation of state or the braking behavior of the surface.