Earth occultation imaging of the low energy gamma-ray sky with GBM

Abstract

Aims. The Earth Occultation Technique (EOT) has been applied to Fermi's Gamma-ray Burst Monitor (GBM) to perform all-sky monitoring for a predetermined catalog of hard X-ray/soft γ-ray sources. In order to search for sources not in the catalog, thus completing the catalog and reducing a source of systematic error in EOT, an imaging method has been developed -Imaging with a Differential filter using the Earth Occultation Method (IDEOM). Methods. IDEOM is a tomographic imaging method that takes advantage of the orbital precession of the Fermi satellite. Using IDEOM, all-sky reconstructions have been generated for ∼4 years of GBM data in the 12-50 keV, 50-100 keV and 100-300 keV energy bands in search of sources otherwise unmodeled by the GBM occultation analysis. Results. IDEOM analysis resulted in the detection of 57 sources in the 12-50 keV energy band, 23 sources in the 50-100 keV energy band, and 7 sources in the 100-300 keV energy band. Seventeen sources were not present in the original GBM-EOT catalog and have now been added. We also present the first joined averaged spectra for four persistent sources detected by GBM using EOT and by the Large Area Telescope (LAT) on Fermi: NGC 1275, 3C 273, Cen A, and the Crab.

Using Gamma Ray Monitoring to Avoid Missing the Next Milky Way Type Ia Supernova

“…Strategies for localization and multimessenger followup appear in the Appendix C. Some early results of our analysis were summarized in (Wang et al 2015). In using burst monitors to search for Milky Way signals, we draw on pioneering blind searches for Galactic point sources (Rodi et al 2014) and diffuse emission (Ng et al 2015).…”

“…Speed and reliability of the alarm will be crucial. There are two possibilities of getting alert of a Galactic SNIa: 1) BAT discovers the SNIa first, or 2) Fermi finds the SNIa first and use the Earth occultation technique (Wilson-Hodge et al 2012;Rodi et al 2014) to localize it within degrees. After the alert by BAT or Fermi, Swift will slew to the SNIa, localize it within arcminutes, and take XRT and UVOT spectra.…”

“…Therefore, the flux for shell model is unknown point sources for GBM (Wilson-Hodge et al 2012;Rodi et al 2014). The occultation duration will depend on the elevation angle β between the source and the orbital plane.…”

Axion constraints from quiescent soft gamma-ray emission from magnetars

“…The 53 day orbital precession period of Fermi can also be used to apply EOT without the use of a predefined source catalogue. Using the Imaging with a Differential Filter using the Earth Occultation Method (IDEOM), the Earth limb is projected onto the sky and used to determine count rates from 600, 000 virtual sources with a 0.25°spacing [46], identifying 17 new sources.…”

Ex Luna, Scientia: The Lunar Occultation eXplorer (LOX)

“…This uniqueness condition is guaranteed by instantaneous occultation onset times (for point sources), which are themselves ensured by the Moon's high density and lack of atmosphere. This instantaneous occultation cannot be achieved from Earth orbit because of its atmosphere [21,48]. Precisely resolving occultation times translates directly into source-localization performance and source-confusion mitigation.…”