  Models of pair-instability supernovae (PISNe) predict a gap in black hole
(BH) masses between $\sim 45M_\odot-120M_\odot$, which is referred to as the
upper BH mass-gap. With the advent of gravitational-wave astrophysics it has
become possible to test this prediction, and there is an important associated
effort to understand what theoretical uncertainties modify the boundaries of
this gap. In this work we study the impact of rotation on the hydrodynamics of
PISNe, which leave no compact remnant, as well as the evolution of
pulsational-PISNe (PPISNe), which undergo thermonuclear eruptions before
forming a compact object. We perform simulations of non-rotating and
rapidly-rotating stripped helium stars in a metal poor environment
$(Z_\odot/50)$ in order to resolve the lower edge of the upper mass-gap. We
find that the outcome of our simulations is dependent on the efficiency of
angular momentum transport, with models that include efficient coupling through
the Spruit-Tayler dynamo shifting the lower edge of the mass-gap upwards by
$\sim 4\%$, while simulations that do not include this effect shift it upwards
by $\sim 15\%$. From this, we expect the lower edge of the upper mass-gap to be
dependent on BH spin, which can be tested as the number of observed BH mergers
increases. Moreover, we show that stars undergoing PPISNe have extended
envelopes ($R\sim 10-1000~R_\odot$) at iron-core collapse, making them
promising progenitors for ultra-long gamma-ray bursts.

High Energy Astrophysical Phenomena;Solar and Stellar Astrophysics