GW170817: $\textit{Swift}$ UV detection of a blue kilonova, and improving the search in O3

$\textit{Swift}$'s rapid slewing, flexible planning, and multi-wavelength instruments make it the most capable space-based follow-up engine for finding poorly localized sources. During O1 and O2 $\textit{Swift}$ successfully tiled hundreds of square-degrees of sky in the LVC localization regions, searching for, and identifying, possible X-ray and UV/O transients in the field. $\textit{Swift}$ made important contributions to the discovery and characterization of the kilonova AT 2017gfo, discovering the UV emission and providing the deepest X-ray upper limits in the first 24 hours after the trigger, strongly constraining the dynamics and geometry of the counterpart. $\textit{Swift}$ tiled 92% of the galaxy convolved error region down to average X-ray flux sensitivities of $10^{-12}$ erg $\mbox{cm}^{-2}$ $\mbox{s}^{-1}$, significantly increasing our confidence that AT 2017gfo is indeed the counterpart to GW 170817 and sGRB 170817. However, there remains significant room for improvement of $\textit{Swift}$'s follow-up in preparation for O3. This will take the form of both revised observation strategy based on detailed analysis of the results from O2, and significant changes to $\textit{Swift}$'s operational capabilities. These improvements are necessary both for maximizing the likelihood that $\textit{Swift}$ finds a counterpart, and minimizing the impact that follow-up activities have on other $\textit{Swift}$ science priorities. We outline areas of improvement to the observing strategy itself for optimal tiling of the LVC localization regions. We also discuss ongoing work on operational upgrades that will decrease latency in our response time, and minimize impact on pre-planned observations, while maintaining spacecraft health and safety.
Comment: 8 pages, 6 figures. Submitted for the proceedings of IAU 338 (Gravitational Wave Astrophysics: Early Results from GW Searches and EM Counterparts)