Fermi Solar Flare Observations

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 Fermi LAT instrument observes gamma-rays above ~20 MeV. The LAT spectrum and response files must be requested from the LAT team.

On a daily basis, we scan the GBM data for solar flares, compile a solar flare list, and generate daily and orbital quicklook plots (most easily viewable through the RHESSI Browser link below). For each flare identified, we also generate a GBM response matrix file.

OSPEX, our IDL spectral analysis package, is used to view the count-rate data as a function of time or energy, as well as to convert the count-rate data into the spectrum of the incident photons using various selectable spectral forms. Input to OSPEX are the daily or trigger count-rate data file (GBM CSPEC or CTIME, or LAT) and the corresponding detector response matrix file.

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.

Reports and Presentations for this Proposal Effort:

• 2009 Fermi Symposium Poster, November 2009
• Progress Report, January 2010
• SPD Poster, May 2010
• Progress Report, January 2011

Fermi Links:

• Fermi Solar Data Analysis Workshop, GSFC, August 22,23, 2012
• Fermi Science Support Center
• Fermi Data Archive
• Max Planck Institute GBM Web Page
• THE FERMI GAMMA-RAY BURST MONITOR, C. Meegan et al 2009 ApJ 702 791
• GBM Detector Orientations
• GBM NaI and BGO Energy Resolution
• GBM NaI and BGO Energy Dependence of Effective Area
• Table of GBM Characteristics
• GBM Team Publications
• Caveats About Analyzing GBM Spectra
• GBM Low-Level Threshold (LLT) Settings Table

Other Links:

• RHESSI Data and Software Center
• Solar Monitor
• HEASARC Archive Browser

Last updated 22 October, 2012 by Kim Tolbert