SVOM (Space-based multiband astronomical Variable Objects Monitor) is a Sino-French mission committed to Gamma-Ray Burst (GRB) studies, in general, to the discovery and multi-wavelength follow-up of cosmic transients. The mission includes a satellite and a dedicated ground segment. The satellite carries two widefield monitors for GRB detection, called ECLAIRs and GRM (Gamma-Ray Monitor), and two narrow-field telescopes for GRB follow-up, called MXT (Microchannel X-ray Telescope) and VT (Visible Telescope). Mechanical structures of SVOM is as Fig 1:

Fig 1: Mechanical structures of SVOM

    The Ground segment encompasses two 1-m class robotic telescopes (C-GFT and F-GFT), a network of wide-field visible cameras (GWACs) and an ensemble of ∼45 VHF receivers distributed in tropical zones at the footprint of SVOM orbit to receive the alerts and forward them to the French Science Center. While the two wide-field monitors will survey large fractions of the sky (∼15% for ECLAIRs and ∼20% for GRM) to look for new high-energy transients, the narrow-field instruments will simultaneously perform multiwavelength observations of selected sources. The detection and localization of a new transient will result in the sending of an alert and the automatic repointing of the satellite, allowing its observation with the on-board X-ray and visible telescopes in minutes. SVOM will adopt a pointing strategy optimized for ground-based follow-up, by observing the sky above the Earth’s night hemisphere. This allows for a large fraction (up to 75 %) of the real-time GRB alerts broadcast by SVOM to be quickly observed by ground-based instruments, fostering space-ground collaborations. When in operation, SVOM will provide many of the capabilities expected from a modern high energy transient mission, such as on-board localizations in seconds and quick alert dissemination, automatic satellite slew, onboard multi-wavelength follow-up, refined localizations in minutes, and the possibility to quickly adjust the observing plan to point targets of opportunity.

    After the Swift project, SVOM will be one of the most promising missions for real-time GRB trigger and localization, GRB afterglow measurement over many energy bands, high-redshift GRB detections. SVOM is expected to be launched in 2024 for a nominal mission of three years, possibly extended by two additional years to initiate observation in a low-earth orbit (LEO) with an altitude of ∼625km and inclination of ∼29 degree.

    The principal scientific objectives is as follow:

 · Permit the detection of all known types of GRBs, with a special care on high-z GRBs.

 · Provide fast, reliable GRB positions.

· Measure the broadband spectral shape of the prompt emission (from the visible to low-energy gamma rays).

 · Measure the temporal properties of the prompt emission.

· Measure the temporal properties of the afterglow emission (from the X-ray to the near infrared domains).

· Quickly identify the afterglows of detected GRBs, including those which are highly redshifted (z > 6).

· Quickly provide sub-arcsecond position and redshift indicators of the afterglows of the detected GRB.

· Provide multi-wavelength observations of celestial sources observable during the General Program, or during GRB follow-up observations, or following ToO requests.