GBM Occultation Project

GBM Earth Occultation Monitored Sources Source Name RA (deg) Dec (deg) 1 V0332+53 53.8 53.2 2 Crab 83.6 22.0 3 A0535+262 84.7 26.3 4 MXB 0656-072 104.6 -7.3 5 Vela X-1 135.5 -40.6 6 GX301-2 186.7 -62.8 7 Cen A 201.4 -43.0 8 Sco X-1 245.0 -15.6 9 Her X-1 254.5 35.3 10 4U1700-377 256.0 -37.8 10 XTE J1752-223 268.1 -22.3 11 GRS 1915+105 288.8 11.0 12 Cyg X-1 299.6 35.2 13 Cyg X-3 308.1 41.0

GBM Occultation Flux Histories The Fermi Gamma-Ray Burst Monitor (GBM) is not a pointed or imaging instrument. To determine fluxes for known sources, we measure the change in the count rate observed in the NaI detectors when the source enters or exits Earth occultation. The measured counts in each energy channel are are converted to fluxes using an assumed spectrum for each source. For these measurements we currently use CTIME data, with 0.256s time bins and 8 energy channels covering 8 keV to 1 MeV. Our technique uses all 8 energy channels, but for most sources the majority of the signal is in channels 1-2, 10-25 keV and 25-50 keV, respectively. These results are preliminary. Please contact Colleen Wilson-Hodge for further information.

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