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January 12, 2009

Voyagers in the Heliosheath Kauai, Hawaii. The IBEX Hi Sensor: Detecting ENAs from the Outer Heliosphere Dan Reisenfeld & the IBEX Team. January 12, 2009. Outline. How instrument subsystems work to provide energy-resolved all-sky ENA distribution Background Rejection

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January 12, 2009

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  1. Voyagers in the Heliosheath Kauai, Hawaii. The IBEX Hi Sensor: Detecting ENAs from the Outer Heliosphere Dan Reisenfeld & the IBEX Team January 12, 2009

  2. Outline • How instrument subsystems work to provide energy-resolved all-sky ENA distribution • Background Rejection • Coincidence measurement technique • Temporal resolution • Predicted count rates • Current status

  3. IBEX-Hi Design: Large Single Pixel ENA Camera • Four major subsystems • Entrance • ENA-to-ion conversion • Energy analysis • Coincidence detector • Entrance • Rejects ions & electrons, collimates neutrals • ENA to ion conversion • Converts neutrals to positive ions • Energy analysis • Selects energy passband • 0.3 – 6 keV • Coincidence Detector • Identifies ENA, rejects noise

  4. Collimator Angular Response • Simulation of single pixel response (measured response matches this)

  5. Calibration Results Match End-to-End Simulation • ESA + foil throughput: Good agreement between IBEX-Hi electro-optic model and calibration results

  6. IBEX-HI Detector Section / Background Monitor Energetic Ion Background Monitor

  7. Instrument Response Functions

  8. Calibrated Geometric Factor • Assuming an energy independent flux over the ESA passband: Values of G from the response function, in cm2 sr eV/eV.

  9. Data Products: Double & Triple Coincidences Long TOF window = 100 ns • 13 coincidence types: Short TOF Window = 7 ns time Start (A,B,C) * Highly unlikely that a trigger in CEM C in the short window is a valid ENA event

  10. Event type probabilities: Triples Event-type ratios can be used to distinguish signal from backgrounds

  11. Noise & Background Rejection • Ions: • energies within passband of ESA transmission rejected by positive potential on collimator • Correlation with background monitor • Electrons: • rejected by negative potential on collimator entrance ring • Photons (Vis, UV & X-ray): • Flux mitigated by 3 foils (conversion & detector section), ESA serration and blackening, coincidence detection • correlation with background monitor • Penetrating radiation: • Triple coincidence, detectors not aligned • correlation with background monitor

  12. Penetrating Background Rates (Calibration)

  13. Continuous Sampling of ENA Measurements vs. ecliptic latitude 6 months • Best statistics at high latitudes • Possibility of observing time variability in heliosheath/TS on time scales < 6 months? 1 month 14 days 7 days

  14. Time Resolution of ENA Measurements Energy width of ESA passbands introduces uncertainty in ENA arrival time Travel time to 100 AU Time uncertainty within energy passbands (60- 120 days) Time [days]

  15. Aspera/MEX Flux and Other Models of ENA Flux at 1 AU ENA flux predictions at a given energy range over ~5 decades!

  16. Predicted IBEX Triple Coincidence Count Rates Increasing sensitivity with energy flattens steep flux distributions Detection Limit

  17. IBEX HI Status • Commissioning completing this week • All systems operating nominally • Detector gains as before launch • Positive ENA detection: • Heliospheric • Magnetospheric

  18. IBEX-HI is performing fantastically… Wait for it! Doubles (aAB) Triples (aABC, bABC, abABC)

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