Spectroscopic Alerts for the Time-Domain Era

TL;DR

Spectroscopic alerts can revolutionize time-domain astronomy by enabling real-time spectral discovery, bridging the gap between the vast number of photometric alerts and limited spectroscopic follow-up capabilities.

Contribution

This paper introduces the concept of spectroscopic alerts and discusses the requirements for a facility capable of real-time spectral discovery in the 2040s.

Findings

Spectroscopic alerts enable real-time spectral analysis of transients.

A proposed facility can handle millions of alerts annually.

Spectroscopic alerts expand discovery potential beyond current follow-up methods.

Abstract

Time-domain astronomy is entering an era of unprecedented discovery driven by wide-field, high-cadence surveys such as LSST, Roman, Euclid, SKA, and PLATO. While some of these facilities will generate enormous photometric alert streams, the physical interpretation of variability and transients often requires spectroscopy, which encodes changes in ionisation state, kinematics, and accretion that are inaccessible to photometry alone. A critical gap is therefore emerging: next-generation surveys may produce up to $\sim10^9$ alerts per year, whereas global spectroscopic follow-up is limited to only $\sim10^4$--$10^5$ transient spectra annually. We present the concept of spectroscopic alerts: real-time notifications triggered by significant spectral evolution, enabling spectroscopy to act as a discovery channel rather than solely as follow-up. We outline the key science cases enabled by this capability and describe the instrumental and operational requirements of a wide-field, highly multiplexed spectroscopic facility capable of delivering real-time spectral discovery for 2040s time-domain and multi-messenger astronomy.