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GLAST-Swift Overlap. David Band, GSSC CRESST/GSFC/UMBC. Issue. GLAST will provide broadband gamma-ray spectra, GeV followups Swift provides burst localizations, X-ray/Opt. followups, narrow-band gamma-ray spectra
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GLAST-Swift Overlap David Band, GSSC CRESST/GSFC/UMBC
Issue • GLAST will provide broadband gamma-ray spectra, GeV followups • Swift provides burst localizations, X-ray/Opt. followups, narrow-band gamma-ray spectra • Complementary mission capabilities for bursts observed by both. Overlap of both LAT and GBM with Swift’s BAT relevant. • Operational questions: • What overlap can we expect? • Can this overlap be improved?
Complementary Spectra GBM’s BGO Count Rate per Log. Energy Band LAT GBM’s NaI Swift’s BAT Energy (keV)
Methodology • Calculate dependence of overlap on angle between FOVs. • Histogram angle between FOVs for simulated GLAST and actual Swift pointing histories. • Compute average overlap. Swift BAT by GLAST LAT Histogram of angles for set of GLAST and Swift pointing histories GLAST LAT by Swift BAT
Results • For one set of GLAST and Swift pointing histories: • GLAST LAT covers 0.28 of Swift BAT FOV • Swift BAT covers 0.13 of GLAST LAT FOV • Beat periods (depends on orbit height, inclination angle, will evolve during mission) • Different orbital periods: side of Earth varies every ~13 day • Different orbit precession periods: difference of ascending nodes varies every ~6.5 years
Optimizing Overlap • GLAST in survey mode: rocks 35 degrees above/below orbital plane once per orbit • Swift performs ~6 pointed observations per orbit • Burst followups • ‘Fill-in’ targets • Optimization strategy (TBS): choose ‘fill-in’ targets that increase the Swift-GLAST overlap. May be as simple as choosing Swift targets on same side of orbital plane as GLAST survey pointing.