SVOM/VT: Overview of data processing and GRB identifications with X-band data

TL;DR

This paper reviews the data processing pipeline for VT X-band data on the SVOM mission, highlighting its high success rate in detecting optical counterparts of GRBs within short timeframes.

Contribution

It provides an overview of the ground-based processing pipeline for VT X-band data and reports on the high detection rates of GRB optical afterglows.

Findings

VT has followed up 111 GRBs as of December 2025.

The overall optical counterpart detection rate is approximately 75%.

Detection rates are 77% within 30 minutes for SVOM/ECLAIRs and 81% for external triggers within 3 hours.

Abstract

VT (the Visible Telescope) is an optical telescope onboard the SVOM (Space-based Multi-band Astronomical Variable Objects Monitor) mission, specifically designed to detect optical counterparts of gamma-ray bursts (GRBs), study their afterglows, and select high-redshift candidates. It performs rapid follow-up observations simultaneously in two channels either via autonomous platform slewing or Target of Opportunity (ToO) observations. The science images acquired by VT and transmitted via the X-band downlink system are designated as VT X-band data. This paper provides an overview of GRB optical afterglow identifications with VT and describes the ground-based processing pipeline for VT X-band data, including preprocessing, astrometric calibration, and photometry. Up to 2025 December 3, VT has followed up 111 GRBs triggered by SVOM or external missions. The overall detection rate of optical counterparts is approximately 75%. Specifically, for bursts detected by SVOM/ECLAIRs, the detection rate is 77% when observed by VT within 30 minutes after the burst. A slightly higher detection rate of 81% is achieved for GRBs triggered by external missions through rapid ToO observations with a mid-time of less than 3 hours.