The 3rd Fermi GBM Gamma-Ray Burst Catalog: The First Six Years

Abstract: Since its launch in 2008, the Fermi Gamma-ray Burst Monitor (GBM) has triggered and located on average approximately two gamma-ray bursts (GRB) every three days. Here we present the third of a series of catalogs of GRBs detected by GBM, extending the second catalog by two more years, through the middle of July 2014. The resulting list includes 1405 triggers identified as GRBs. The intention of the GBM GRB catalog is to provide information to the community on the most important observables of the GBM detected GRBs. For each GRB the location and main characteristics of the prompt emission, the duration, peak flux and fluence are derived. The latter two quantities are calculated for the 50-300~keV energy band, where the maximum energy release of GRBs in the instrument reference system is observed, and also for a broader energy band from 10-1000 keV, exploiting the full energy range of GBM's low-energy NaI(Tl) detectors. Using statistical methods to assess clustering, we find that the hardness and duration of GRBs are better fitted by a two-component model with short-hard and long-soft bursts, than by a model with three components. Furthermore, information is provided on the settings and modifications of the triggering criteria and exceptional operational conditions during years five and six in the mission. This third catalog is an official product of the Fermi GBM science team, and the data files containing the complete results are available from the High-Energy Astrophysics Science Archive Research Center (HEASARC).

The 3rd Fermi GBM Gamma-Ray Burst Catalog: A Comprehensive Analysis of the First Six Years

This paper presents the third installment of the Fermi Gamma-ray Burst Monitor (GBM) gamma-ray burst (GRB) catalog, covering six years from its inception since the launch of the Fermi satellite in 2008. The paper provides an extensive dataset consisting of 1405 triggers identified as GRBs and detailed analyses of their characteristics, making it a pivotal resource for the astrophysics community. The catalog's emphasis is on making available crucial observable features of GRBs detected by the GBM, including location, prompt emission properties, duration, peak flux, and fluence across multiple energy bands.

Main Contributions and Findings

1. Comprehensive Dataset: The six-year dataset records 3350 triggers with a breakdown of 1405 as GRBs, complementing these with terrestrial gamma-ray flashes, solar flares, and other celestial phenomena, thus enriching the field's understanding of transient astronomical events.
2. Energy Band Analysis: Key parameters like peak flux and fluence are evaluated over the 50-300 keV and 10-1000 keV energy ranges, accounting for the primary energy release bands observed in GRBs. This energy flexibility allows in-depth spectral studies across a broad bandwidth.
3. Two-Component Model Verification: Through rigorous statistical methods, the study corroborates findings from earlier analyses about GRB classification. It confirms that GRBs' hardness and duration are best represented by a two-component model—characterizing short-hard and long-soft bursts—rather than a three-component model.
4. Triggering Criteria Details: The catalog delineates the settings and modifications of the GBM hardware and software, especially during the fifth and sixth years of the mission, including the adaptation of triggering algorithms and operational conditions, enhancing burst detection and classification capabilities.
5. Improved Localization Techniques: The catalog benefits from advanced localization methods combining onboard and on-ground analyses, yielding an average accuracy of approximately 8 degrees onboard and an improved 4 degrees post-factum.

Implications and Speculations

This catalog serves as an indispensable archive for the GRB research community, facilitating the cross-referencing of events observed by different telescopes and triggering numerous ground-based follow-up studies. Such comprehensive data aid in constraining theoretical models of GRB progenitors and emission mechanisms.

The completeness and detail of the catalog provide opportunities for future studies on GRB localization, dynamic range investigations, and potential correlations with other astrophysical phenomena detected in multi-messenger astronomy. The statistical confirmation of a two-component model invites further inspection into the intrinsic characteristics of GRBs, potentially influencing models of stellar collapse and neutron star mergers.

Future Developments

Looking ahead, the continuation of this cataloging effort could align synergistically with advancements in multi-messenger astronomy, particularly with upcoming gravitational wave detectors. The continuous evolution of the GBM technology and methodology, touching upon aspects like real-time data synthesis and analysis, positions it to contribute decisively to high-energy astrophysics.

Overall, the third Fermi GBM GRB catalog stands as a remarkably thorough recount of the first six years of GRB observations, underscoring the intrinsic value of long-term, systematic data collection and analysis in understanding high-energy phenomena across the universe.