Three years of Fermi GBM Earth Occultation Monitoring: Observations of Hard X-ray/Soft Gamma-Ray Sources

TL;DR

This paper reports on three years of Fermi GBM Earth occultation data analysis, detecting nearly 100 high-energy sources and discussing the technique's challenges, results, and future prospects in gamma-ray astronomy.

Contribution

It presents the first three-year catalog of sources detected via Earth occultation with Fermi GBM, including methodological insights and detection of new transient sources.

Findings

Detected 99 sources, including X-ray binaries, active galaxies, and the Crab Nebula.

Identified sources in the 100-300 keV and 300-500 keV energy bands.

Enhanced detection of transient and persistent sources over three years.

Abstract

The Gamma ray Burst Monitor (GBM) on board Fermi Gamma-ray Space Telescope has been providing continuous data to the astronomical community since 2008 August 12. We will present the results of the analysis of the first three years of these continuous data using the Earth occultation technique to monitor a catalog of 209 sources. Although the occultation technique is in principle quite simple, in practice there are many complications including the dynamic instrument response, source confusion, and scattering in the Earth's atmosphere, which will be described. We detect 99 sources, including 40 low-mass X-ray binary/neutron star systems, 31 high-mass X-ray binary/neutron star systems, 12 black hole binaries, 12 active galaxies, 2 other sources, plus the Crab Nebula and the Sun. Nine of these sources are detected in the 100-300 keV band, including seven black-hole binaries, the active galaxy Cen A, and the Crab. The Crab and Cyg X-1 are also detected in the 300-500 keV band. GBM provides complementary data to other sky monitors below 100 keV and is the only all-sky monitor above 100 keV. In our fourth year of monitoring, we have already increased the number of transient sources detected and expect several of the weaker persistent sources to cross the detection threshold. I will briefly discuss these new sources and what to expect from our five year occultation catalog.