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The GRB joint scientific analysis pipeline of the ECLAIRs and GRM instruments on board SVOM

This paper introduces the `eclgrm` pipelines developed at the French Science Center of SVOM, which perform joint real-time and offline analysis of ECLAIRs and GRM instrument data to provide comprehensive broadband temporal and spectral characterization of Gamma-Ray Bursts.

Original authors: F. Piron, F. Daigne, T. Maiolino, P. Maeght, U. Jacob, M. G. Bernardini, D. Corre, J. Wang, F. Lacreu, G. Tcherniatinsky, L. Domisse, T. Barlyaeva, A. Maïolo, J. -L. Atteia, L. Bouchet, M. Brunet, J.

Published 2026-04-28

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CC BY 4.0

Original authors: F. Piron, F. Daigne, T. Maiolino, P. Maeght, U. Jacob, M. G. Bernardini, D. Corre, J. Wang, F. Lacreu, G. Tcherniatinsky, L. Domisse, T. Barlyaeva, A. Maïolo, J. -L. Atteia, L. Bouchet, M. Brunet, J. -P. Dezalay, O. Godet, S. Guillot, H. Yang, B. Arcier, S. Mate, N. Dagoneau, L. Jouvin, K. Tazhenova, T. Sadibekova, P. Bacon, N. Bellemont, F. Cangemi, A. Coleiro, J. He, Y. Huang, L. Li, H. Shi, J. Wang, P. Wang, L. Zhang, X. -Y. Zhao, S. Zheng

Original paper licensed under CC BY 4.0 (http://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

The Cosmic Detective Agency: How SVOM Catches Space Explosions

Imagine you are a detective in a massive, dark city. Suddenly, a firework goes off in a distant alleyway. To solve the mystery of what happened, you need more than just a quick glance; you need high-speed cameras, specialized sensors to detect heat, and a way to instantly organize all that evidence before the trail goes cold.

This paper describes the "Digital Detective Agency" built for a new space satellite called SVOM. This satellite is designed to catch Gamma-Ray Bursts (GRBs)—the most violent, energetic explosions in the universe.

Here is how the "agency" works, broken down into simple terms.

1. The Two Specialized Detectives (The Instruments)

The satellite has two main "eyes" that see different things:

ECLAIRs (The High-Definition Camera): This instrument sees "soft" X-rays. Think of it like a camera that captures the subtle colors and details of the explosion.
GRM (The Heat Sensor): This instrument sees "hard" gamma rays. It’s like a thermal sensor that detects the raw, intense heat of the blast.

By combining these two, scientists don't just see that something exploded; they see the full "color palette" of the energy, from the gentle glow to the blinding flash.

2. The Two Speed-Dial Systems (The Pipelines)

When an explosion happens, the data starts flooding in. The scientists use two different "processing pipelines" to handle the information, depending on how much time they have.

The "Quick Response" Team (The VHF Pipeline)

The Analogy: Imagine a 911 dispatcher.
What it does: As soon as the satellite detects a flash, this system kicks into gear. It works in less than a minute. It doesn't give you a full biography of the explosion, but it tells you: "Hey! Something just happened! It was big, it lasted 5 seconds, and it's located in this direction!"
The Goal: To alert astronomers on Earth immediately so they can point their big telescopes at the spot before the light fades.

The "Forensic Lab" (The X-band Pipeline)

The Analogy: This is the CSI lab that arrives hours later.
What it does: Once the satellite sends back the full, high-resolution files, this pipeline performs a deep dive. It reconstructs the entire "crime scene." It calculates exactly how much energy was released, how the light changed over time, and the precise "fingerprint" (the spectrum) of the explosion.
The Goal: To understand the physics of the explosion—was it a star collapsing? Two black holes colliding? This is where the real science happens.

3. The Control Room (The User Interface)

Even with all this automation, you still need a human "Chief of Police." The paper describes a software interface called eclgrm-ui.

Think of this as a Mission Control dashboard. It allows a scientist on duty to watch the automated "detectives" working in real-time. If the computer makes a mistake or if a scientist wants to look closer at a specific detail, they can step in, tweak the settings, and "re-run" the analysis manually to get a clearer picture.

Summary: Why does this matter?

Space is huge, and GRBs are incredibly brief and unpredictable. If we don't have a system that can detect (the eyes), alert (the quick pipeline), and analyze (the forensic pipeline) almost instantly, we miss the most important moments of cosmic history.

This paper is essentially the "Instruction Manual" for the digital brain that ensures SVOM never misses a beat when the universe decides to put on a light show.

Technical Summary: The GRB Joint Scientific Analysis Pipeline of the ECLAIRs and GRM Instruments on Board SVOM

1. Problem Statement

The SVOM (Space-based multi-band astronomical Variable Objects Monitor) mission is designed to study Gamma-Ray Bursts (GRBs) across a broad energy spectrum. To fully characterize the prompt high-energy emission of these transients, it is essential to combine data from two distinct wide field-of-view instruments: ECLAIRs (4–150 keV, coded-mask camera) and the Gamma-Ray Monitor (GRM) (0.015–5 MeV).

The scientific challenge lies in the need for two distinct types of analysis:

Rapid Analysis: Immediate characterization of triggers to facilitate ground-based follow-up.
Comprehensive Analysis: Detailed temporal and spectral reconstruction using high-fidelity event data.
The paper addresses the need for an integrated, automated, and interactive software architecture capable of merging these two data streams to provide a seamless broad-band view of GRB physics.

2. Methodology

The authors developed the eclgrm pipelines, deployed in Docker containers at the SVOM French Science Center (FSC). The system is divided into two primary operational modes:

eclgrm-vhf (Quick Analysis Pipeline):
- Trigger: Activated immediately following onboard alerts transmitted via VHF antennas.
- Process: Analyzes onboard count rate light curves (OBLCs). It employs the Bayesian Blocks method to identify background intervals and uses two background models: Model-T (polynomial of time) and Model-E (polynomial of the cosine of the angle to the Earth's center) to account for orbital modulation.
- Outputs: Rapidly generates light curves, duration estimates ( $T_{90}$ , $T_{80}$ , $T_{50}$ ), peak fluxes, hardness ratios, and crude event classifications.
eclgrm-xband (Complete Analysis Pipeline):
- Trigger: Activated when full event data is transmitted via X-band antennas.
- Process: Performs a deep dive into calibrated event data. It utilizes both counting techniques (for GRM) and imaging techniques (for ECLAIRs) to build count spectra. Spectral modeling is performed via a Python interface to Xspec, testing models like the Band function and power laws.
- Outputs: High-resolution light curves, time-resolved spectra, spectral energy distributions (SEDs), spectral lags, and rest-frame energetics.
eclgrm-ui (User Interface):
- A monitoring and interactive tool that allows the Instrument Scientist (IS) to oversee automated processes, inspect quality control plots, and manually re-run tasks with optimized parameters to refine scientific results.

3. Key Contributions

Integrated Broad-band Framework: The creation of a unified pipeline that bridges the gap between soft X-rays (ECLAIRs) and high-energy gamma rays (GRM), covering an energy range from 4 keV to 5 MeV.
Dual-Speed Processing: Implementation of a tiered architecture that satisfies both the urgency of time-domain astronomy (VHF) and the precision required for publication-quality physics (X-band).
Automated Background Modeling: Development of sophisticated models (specifically Model-E) to handle the complex, time-varying background caused by the satellite's quasi-antisolar pointing and Earth occultation.
Interactive Validation Workflow: The eclgrm-ui provides a human-in-the-loop mechanism to ensure the high reliability of the automated Scientific Data Products (SDPs).

4. Results

The pipelines have been operational since the SVOM launch in June 2024. Key performance indicators include:

Speed: Quick analysis (vhf) typically completes in less than one minute; complete analysis (xband) completes within approximately 15 minutes.
Data Volume: For every GRB candidate detected by both instruments, the pipeline generates over 40 unique scientific data products in FITS format.
Spectral Accuracy: Demonstrated through joint fits (e.g., GRB 241018A) where the pipeline successfully combined ECLAIRs and GRM data to produce high-quality spectra with low reduced statistics, meeting or exceeding the mission's strict flux calibration requirements ( $\pm 20\%$ ).

5. Significance

This work is foundational for the SVOM mission's scientific success. By providing a rapid, automated, and highly accurate analysis pipeline, the eclgrm system enables:

Rapid Multi-messenger Follow-up: Providing immediate localization and characterization to ground-based telescopes.
Advanced GRB Physics: Allowing researchers to investigate thermal components, spectral breaks, and the evolution of short vs. long GRB sub-classes through broad-band spectral coverage.
Standardized Data Dissemination: Ensuring that high-quality, validated data is promptly available to the global community via GCN circulars and public tables.