The study of transient and variable events, including novae, active galactic nuclei, and black hole binaries, has historically been a fruitful path for elucidating the evolutionary mechanisms of our universe. The study of such events in the millimeter and submillimeter is, however, still in its infancy. Submillimeter observations probe a variety of materials, such as optically thick dust, which are hard to study in other wavelengths. Submillimeter observations are sensitive to a number of emission mechanisms, from the aforementioned cold dust, to hot free-free emission, and synchrotron emission from energetic particles. Study of these phenomena has been hampered by a lack of prompt, high sensitivity submillimeter follow-up, as well as by a lack of high-sky-coverage submillimeter surveys. In this paper, we describe how the proposed Atacama Large Aperture Submillimeter Telescope (AtLAST) could fill in these gaps in our understanding of the transient universe. We discuss a number of science cases that would benefit from AtLAST observations, and detail how AtLAST is uniquely suited to contributing to them. In particular, AtLAST's large field of view will enable serendipitous detections of transient events, while its anticipated ability to get on source quickly and observe simultaneously in multiple bands make it also ideally suited for transient follow-up. We make theoretical predictions for the instrumental and observatory properties required to significantly contribute to these science cases, and compare them to the projected AtLAST capabilities. Finally, we consider the unique ways in which transient science cases constrain the observational strategies of AtLAST, and make prescriptions for how AtLAST should observe in order to maximize its transient science output without impinging on other science cases.
Keywords: Time domain; submillimeter; transient phenomena; variability.
A wide range of objects and processes observable in the universe vary temporally on scales ranging from minutes to years. On timescales of a few hours, cosmic magnetic fields can change their configurations, releasing energy as radiation and particle streams. On time scales of weeks to years, young stars are known to vary in luminosity as they accrete mass. The submillimeter radio wavelength regime provides a unique opportunity to observe these phenomena, being sensitive to processes that only emit in that range or are otherwise hidden by dust. So far, however, this field has been limited by a combination of insufficient sky area coverage, poor sensitivity, or poor spatial resolution. Contemporary facilities providing wide field views have small collecting areas, limited sensitivity, and poor spatial resolution. On the other hand, interferometric telescopes such as the Atacama Large Millimeter Array (ALMA) are sensitive and have very fine spatial resolution, but are limited by small fields of view. The Atacama Large Aperture Submillimeter Telescope (AtLAST) will enable major breakthroughs in the exploration of time-variable phenomena in the submillimeter wavelength regime. Thanks to its 50 m diameter, it will resolve details ~ 3 × smaller than current single-dish telescopes. At the same time, AtLAST will outdo both singledish telescopes and interferometers in terms of field of view (FoV) by a factor of several thanks to its instantaneous > 1 deg 2 reach. If AtLAST is fully funded, it would be construction ready by the end of the decade, with first light in the mid 2030s. The AtLAST project is moving forward with a new development phase funded by the EU for 4M EUR. The new project “Consolidating plans for the Atacama Large Aperture Submillimeter Telescope” will start in January 2025 and end in 2028, and it will be carried out by a significantly expanded consortium of 20 Partners from Europe, Asia and Africa. In this paper we present scientific cases where AtLAST will be transformational in our investigation of the time variable submillimeter sky. We summarize how these observations will help us to better understand fundamental processes in astrophysics, such as the formation of stars, their death, and the relics of their passing. We will also lay out the demands that these observations impose on the design of the telescope and its operations.
Copyright: © 2025 Orlowski-Scherer J et al.