[Paper Review] The THESEUS space mission: science goals, requirements and mission concept

L. Amati, P. T. O’Brien+32 more|arXiv (Cornell University)|Jan 1, 2021

Gamma-ray bursts and supernovaePhysics and Astronomy65 references80 citations

TL;DR

THESEUS is a proposed ESA M5 mission concept designed to study high-redshift gamma-ray bursts (GRBs) and multi-messenger transients using a multi-wavelength payload with wide-field X-ray and near-infrared (NIR) capabilities. By detecting and localizing GRBs with high sensitivity and rapid on-board processing, it aims to probe cosmic reionization, early star formation, and the first galaxies, while enabling real-time alerts for gravitational wave and neutrino counterparts.

ABSTRACT

THESEUS, one of the two space mission concepts being studied by ESA as candidates for next M5 mission within its Comsic Vision programme, aims at fully exploiting Gamma-Ray Bursts (GRB) to solve key questions about the early Universe, as well as becoming a cornerstone of multi-messenger and time-domain astrophysics. By investigating the first billion years of the Universe through high-redshift GRBs, THESEUS will shed light on the main open issues in modern cosmology, such as the population of primordial low mass and luminosity galaxies, sources and evolution of cosmic re-ionization, SFR and metallicity evolution up to the “cosmic dawn” and across Pop-III stars. At the same time, the mission will provide a substantial advancement of multi-messenger and time-domain astrophysics by enabling the identification, accurate localisation and study of electromagnetic counterparts to sources of gravitational waves and neutrinos, which will be routinely detected in the late ‘20s and early ‘30s by the second and third generation Gravitational Wave (GW) interferometers and future neutrino detectors, as well as of all kinds of GRBs and most classes of other X/gamma-ray transient sources. Under all these respects, THESEUS will provide great synergies with future large observing facilities in the multi-messenger domain. A Guest Observer programme, comprising Target of Opportunity (ToO) observations, will expand the science return of the mission, to include, e.g., solar system minor bodies, exoplanets, and AGN.

Motivation & Objective

• Investigate the early Universe by observing high-redshift GRBs to probe cosmic reionization, star formation, and metallicity evolution.
• Enable real-time detection and localization of high-energy transients to support multi-messenger astronomy with gravitational wave and neutrino counterparts.
• Advance time-domain astrophysics by monitoring transient sources across the X-ray and near-infrared bands with high sensitivity and rapid response.
• Provide a cornerstone role in the 2030s multi-messenger era by integrating with next-generation facilities like ATHENA, ELT, and third-generation GW detectors.
• Maximize scientific return through a Guest Observer programme, including Target of Opportunity (ToO) observations and public data policies.

Proposed method

• Utilize a wide-field X-ray imager (XGIS) and a soft X-ray imager (SXI) covering 0.3 keV to 10 MeV for deep, all-sky monitoring.
• Integrate on-board near-infrared (NIR) instruments for rapid transient identification, arcsecond localization, and redshift determination within minutes of trigger.
• Implement autonomous spacecraft systems with agile pointing and rapid downlink of trigger alerts to ground stations within seconds.
• Employ a multi-instrument payload with high grasp and angular resolution to detect and characterize GRB afterglows and other transients.
• Establish a Science Data Centre (SDC) with real-time monitoring, alert dissemination, and a ToO screening team to prioritize transient triggers.
• Operate under a science management plan ensuring public data release within hours, with limited proprietary periods for high-redshift GRB data (e.g., 6 months for z > 6).

Experimental results

Research questions

• RQ1 How can high-redshift GRBs be used to probe the cosmic reionization history and the properties of the first galaxies?
• RQ2 What is the role of GRBs in tracing star formation and metallicity evolution during the 'cosmic dawn' (z > 6)?
• RQ3 How can THESEUS enable early detection and localization of electromagnetic counterparts to gravitational wave and neutrino events in the 2030s?
• RQ4 What is the optimal data policy and science management framework to maximize community engagement and scientific return?
• RQ5 How can the mission’s multi-wavelength capabilities improve the selection and follow-up of transient sources for future large facilities?

Key findings

• THESEUS is projected to detect and localize high-redshift GRBs (z > 6) at a rate of ~1 per year, significantly exceeding the cumulative detection rate of the last 20 years.
• The mission’s wide-field X-ray and NIR instruments will enable arcsecond-level localization and redshift determination within minutes of a GRB trigger.
• The on-board autonomous system will transmit trigger alerts to ground within seconds, enabling rapid follow-up by ground-based and space-based telescopes.
• The mission will achieve a 1000× improvement in sensitivity for detecting high-redshift GRB afterglows compared to previous missions.
• The science management plan ensures public data release within hours, with only a 6-month proprietary period for the highest-redshift GRBs (z > 6).
• The Guest Observer programme will allow community-led observations, including ToO triggers and survey-mode pointing adjustments, with a 3-month proprietary period for GO data.