The Fermi GBM instrument consists of twelve NaI detectors pointing in various directions, and two BGO detectors pointing in opposite directions. The NaI detectors measure the low-energy spectrum from 8 keV (nominally, see Note 1 below) to 1 MeV; the BGO detectors cover the higher range of ~200 keV to ~40 MeV. The GBM NaI and BGO data are available in two forms:
- CSPEC files - 128 energy channels, 4.096 s nominal time resolution, 1.024 s during bursts
- CTIME files - 8 energy channels, 0.256 s nominal time resolution, 0.064 s during burst
There are daily files and trigger files (burst and surrounding data) for each detector. NaI detectors are labeled n0 through nb; BGO detectors are labeled b0 and b1. n0 through n5 are usually the sunward NaI detectors (with constantly changing angles), and b0 is always the sunward BGO detector. The names of the daily files include the detector number and the date. For example,
glg_cspec_n2_120508_v00.pha is the daily CSPEC file for NaI detector n2 for May 8, 2012
glg_ctime_n4_120508_v00.pha is the daily CTIME file for NaI detector n4 for May 8, 2012
glg_cspec_n0_bn120508545_v00.pha is the trigger file for the burst that occurred an May 8, 2012, at fraction of day=.545
Note 1: In order to reduce count rates during periods of high solar activity, the low energy threshold of the sunward NaI detectors is raised periodically. Please see the LLT Settings Table.
The Fermi LAT instrument is sensitive to gamma-rays between ~20 MeV and 300 GeV. In normal sky-survey mode, the detector axis rocks ~50º from the zenith each orbit, so usually the Sun is observed for ~20-40 minutes every two orbits (~3 hours).
The full Fermi data set and the general suite of analysis tools provided by the Fermi project are accessible through the Fermi Science Support Center (FSSC). To create these solar products, we used the FSSC data and elements of the FSSC software.
Last updated 25 November, 2013 by Kim Tolbert