GLAST-Swift Overlap

1
GLAST-Swift Overlap

• David Band, GSSC
• CRESST/GSFC/UMBC

2
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 Swifts BAT relevant.
• Operational questions
• What overlap can we expect?
• Can this overlap be improved?

3
Complementary Spectra
GBMs BGO
Count Rate per Log. Energy Band
LAT
GBMs NaI
Swifts BAT
Energy (keV)
4
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
5
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

6
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.