UV and X-ray Observations of Shock Breakout

Time-domain astrophysical objects such as supernovae and gamma-ray bursts are central to compact object formation, heavy element creation, and multi-messenger astronomy. They are strongly associated with many areas of astrophysics. Because of this association, observational data of these objects have mushroomed over the last decade, including UV supernova data from the NASA Neil Gehrels Swift Observatory and the first gravitational and electromagnetic wave detection of a neutron star merger. Unfortunately, most of these observations occur after the initial explosion when interactions with the surrounding environment shrouds our interpretations of the observations. The most penetrating and critical observations of these transients and their progenitors require a prompt observation in the X-ray and UV when the first photons appear. The Shock Interaction and Breakout EXplorer (SIBEX) is a proposed MIDEX mission designed to obtain the earliest supernovae and neutron star merger observations. SIBEX accomplishes this by monitoring large areas of the sky to detect the earliest supernova and neutron star merger photons by using its very wide field-of-view soft X-ray telescopes (XRF) to localize outbursts. Immediately after a localization is provided by XRF, a rapidly slewing spacecraft autonomously positions a co-located narrow-field UV telescope (SUSI) on the provided position. A refined position is provided by SUSI from which the spacecraft repositions SUSI in order to place its spectroscopic slit on the source in order to probe the outburst environment. No other past, present, or planned observatories have the combined SIBEX X-ray and UV capabilities for exploring ~50 shock breakouts of supernovae and ~25 neutron star mergers in a three year mission. In this talk, we examine the science gains obtained by combining the earliest UV and X-ray observations of these time-domain objects, as well as a review of the mission and corresponding instruments.