THESEUS Scientific Requirements

THESEUS is designed to achieve two primary scientific goals:

  1. Explore the early Universe by providing a complete census of GRBs in the first billion years.

  2. Perform an unprecedentedly deep monitoring of the X-ray transient Universe thus playing a fundamental role in the coming era of multi-messenger and time-domain astrophysics

These goals are very demanding in terms of technology and require a combination of on-board capability to perform wide-field X-ray imaging, the ability to obtain broad bandpass X-ray spectra and to localise and characterise the high-energy transients in the optical-IR. The conversion from THESEUS science goals to instrument and spacecraft requirements are shown in the flow chart below:

To meet the science requirements requires the provision of three instruments on board: a wide-field soft X-ray monitor with imaging capability (the SXI); a harder X-ray, non-imaging spectroscopic instrument with the same field of view as the SXI (the XGIS); and an optical/near-IR telescope with both imaging and spectroscopic capability (the IRT).

The spacecraft needs to be agile (fast response to enable the IRT to detect the source) and be able to rapidly communicate triggers to the ground so as to enable other observatories to also follow-up the new transients. The ability to point the spacecraft into the night sky (anti-solar) direction for part of the orbit enhances rapid ground follow-up capability to provide additional (multi-wavelength) data. Capability for stable 3-axis pointing for >1ksec is required to detect the longest duration transients.

 

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Table 1. Flow-chart showing the logical path from main science goals to instruments and mission requirements.