**3. Science Cases**

In the following, we give a description of the SVOM main observing programs, the GRB "core" program, the general program, and the Target of Opportunities (ToOs) program. For a complete discussion of all the science cases related to these programs, we refer to Wei, Cordier et al. (2016) [1].

The core program: Thanks to the unique properties of the mission outlined in Section 2, SVOM will provide a unique sample of ∼30–40 GRBs/yr with: (i) Complete coverage of the prompt emission over three decades in energy, thanks to the synergy between ECLAIRs and GRM (see e.g., Figure 3 and [2]), and possibly the detection of the prompt optical counterpart with the GWAC (∼16% of cases); (ii) the X-ray counterpart observed from a few minutes after the trigger up to a few days in X-rays, optical, and NIR; and (iii) a redshift measurement for ∼2/3 of them, allowing for a complete study of their physical properties in the rest frame. The low-energy threshold of ECLAIRs and the extension to the NIR of the GFTs will allow SVOM to tackle many open issues in GRBs science, as high-redshift GRBs (z > 5) that allows to probe the primordial universe, or soft GRBs (X-ray rich and X-ray flashes) and ultra-long GRBs ([3,4], see also Figure 3) that will shed light to the nature of

the progenitors in the local universe and the physics of explosion. The joint observations of ECLAIRs and GRM will increase the efficiency in detecting short GRBs that, besides their interest per se, are one of the possible counterparts of Gravitational Wave (GW) emitters. Finally, the possible detection (or limits from the non-detection) of the optical counterpart of the GRB prompt emission will open a new window for unexpected discoveries.

**Figure 3. Left panel:** The multi-component (band plus blackbody) prompt emission spectrum of the Fermi/GBM detected GRB 100724B, simulated as it would have been seen by ECLAIRs and GRM. The two instruments together will be capable to well characterize the peak energy and all the features of the prompt emission of GRBs. Adapted with permission from ref. [2], Copyright Year: 2017, Copyright Owner: Springer. **Right panel:** ECLAIRs on-axis count Signal-to-Noise ratio (SNR) for short high-energy transients in the local Universe: Long and Short GRBs (LGRB, SGRB), X-ray Flashes (XRF), ultra-long GRBs (ulGRBs), and Soft Gamma-ray Repeater (SGR) giant flares. The orange horizontal band represents the detection threshold of ECLAIRs at SNR = 6.5. The green and yellow bands represent the O4 LIGO distance sensitivity limits for double neutron stars and neutron star-black hole mergers, respectively. The light grey trails represent the evolution of the on-axis count SNR with the redshift. Adapted with permission from ref. [4], Copyright Year: 2020 Copyright Owner: Springer.

The general program: Although SVOM is a mission specifically designed for GRB science, its characteristics will find many applications in the study of many extra-galactic sources as Active Galactic Nucleai (AGN), Ultra-Luminous X-ray sources (ULX), and Tidal Disruption Events (TDE), and galactic sources as accreting systems, pulsars, magnetars, and flaring stars.

Rapid follow-up observations: Thanks to its flexibility, SVOM will be a powerful tool for the multi-wavelength follow-up of transients discovered by external facilities and not triggered by SVOM. This will be possible thanks to a Target of Opportunities (ToOs) program. SVOM will take advantage from wide-field instruments such as ECLAIRs, GRM, and GWAC to search for the counterparts at different wavelengths of events discovered by external facilities, and also of an X-ray telescope (MXT) with a field of view of 1 deg<sup>2</sup> that will allow SVOM to cover larger regions than Swift/XRT. This will be particularly important to identify the Electromagnetic (EM) counterparts of GW or neutrino emitters. Indeed, SVOM will have a specific ToO program dedicated to EM counterpart search in response to a multi-messenger alert. Concerning GW alerts, SVOM already joined the first three observing runs of the Advanced LIGO and Virgo interferometers with part of the ground segment (see e.g., [5]), and will be ready to join the first part of O4 (starting in late 2022) with its ground-based instruments before the launch of the spacecraft.
