GRBs and Relativistic Transients in the 2040s

Relativistic transients such as gamma-ray bursts (GRBs), jetted tidal disruption events, luminous fast blue optical transients, and fast X-ray transients, represent the brightest explosions in the Universe and serve dual roles as laboratories for extreme physics and as cosmic lighthouses probing the earliest epochs of the Universe. The 2040s will bring transformative capabilities: wide-field optical surveys discovering tens of thousands of optical transients nightly, proposed high-energy missions like THESEUS providing 10-100x improved high-energy monitoring, and third-generation gravitational wave detectors identifying $\mathcal{O}(10^5)$ compact object mergers annually, many accompanied by relativistic jets. This industrial-scale discovery rate will enable population studies addressing fundamental questions such as jet launching mechanisms, nucleosynthesis, the first stars, and how progenitor environments shape these transients across cosmic time. However, realizing this science requires overcoming a critical bottleneck: these transients evolve on timescales of seconds to days, with their physics encoded in rapidly-changing multi-wavelength signatures demanding immediate spectroscopic characterization down to m ~ 25. Current facilities, optimized for classical/queue scheduling, do not provide the rapid, flexible, multi-target response necessary for industrial-scale follow-up. This white paper demonstrates that without a dedicated large-aperture (10-30 m effective collecting area) time-domain facility with robotic scheduling and optical-NIR spectroscopic capabilities, the transformative potential of relativistic transient science in the 2040s will be considerably limited.

💡 Research Summary

This white paper argues that the coming “industrial‑scale” era of relativistic transients in the 2040s—gamma‑ray bursts, jetted tidal‑disruption events, luminous fast blue optical transients, fast X‑ray transients, and ultra‑long GRBs—will demand a dedicated, large‑aperture (10–30 m effective collecting area) time‑domain facility with robotic scheduling and optical‑NIR spectroscopic capability. Upcoming facilities such as LSST, THESEUS, and third‑generation gravitational‑wave observatories (Einstein Telescope, Cosmic Explorer) will generate tens of thousands of alerts per night and detect up to 10⁵ compact‑object mergers per year, many accompanied by relativistic jets. The scientific payoff is enormous: probing jet launching mechanisms (internal shocks, magnetic reconnection, photospheric emission), mapping jet structure and magnetic field geometry, determining the success‑or‑failure fraction of jets, characterizing progenitor environments across cosmic time, measuring long‑lived energy injection (magnetar spin‑down vs fallback), uncovering the power sources of the most luminous explosions (LFBOTs), and using high‑z GRBs as backlights to study the first stars, reionization, and r‑process nucleosynthesis. However, the bottleneck is rapid, multi‑wavelength characterization. Relativistic transients evolve on seconds‑to‑days timescales, and their physics is encoded in swiftly changing spectra that must be obtained down to m ≈ 25 mag. Current large telescopes operate on classical or queue scheduling and cannot respond within minutes to dozens of simultaneous targets; smaller robotic telescopes lack the collecting area for faint, high‑redshift events. The authors therefore propose a new facility that combines (i) automatic alert ingestion and precise localization, (ii) fast‑slewing (< seconds) to any sky position, (iii) simultaneous optical‑NIR spectroscopy at R ≈ 2,000–10,000 for 5–10 events per night, (iv) an auxiliary imaging camera for rapid counterpart identification, and (v) coordinated sub‑mm/radio follow‑up. Such a system would enable real‑time redshift measurement, velocity structure analysis, and detection of high‑z absorption features, turning the flood of alerts into a statistically robust sample. With this capability, the community could conduct population studies of up to 10⁵ mergers and thousands of GRBs per year, finally answering the nine key science questions outlined in the paper and cementing ESO’s leadership in time‑domain astrophysics for the 2040s.