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

2 The IBEX-HI SensorVoyagers in the Heliosheath Conference, January 12, 2009 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 The IBEX-HI SensorVoyagers in the Heliosheath Conference, January 12, 2009 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 ENA IBEX-Hi Design: Large Single Pixel ENA Camera

4 The IBEX-HI SensorVoyagers in the Heliosheath Conference, January 12, 2009 Collimator Angular Response Simulation of single pixel response (measured response matches this)

5 The IBEX-HI SensorVoyagers in the Heliosheath Conference, January 12, 2009 Calibration Results Match End-to-End Simulation ESA + foil throughput: Good agreement between IBEX-Hi electro-optic model and calibration results

6 The IBEX-HI SensorVoyagers in the Heliosheath Conference, January 12, 2009 IBEX-HI Detector Section / Background Monitor Background Monitor Energetic Ion

7 The IBEX-HI SensorVoyagers in the Heliosheath Conference, January 12, 2009 Instrument Response Functions

8 The IBEX-HI SensorVoyagers in the Heliosheath Conference, January 12, 2009 Calibrated Geometric Factor Assuming an energy independent flux over the ESA passband: Values of G from the response function, in cm 2 sr eV/eV. ESA SettingG (summed doubles)G (qualified triples)

9 The IBEX-HI SensorVoyagers in the Heliosheath Conference, January 12, 2009 Data Products: Double & Triple Coincidences Short TOF Window = 7 ns Long TOF window = 100 ns Start (A,B,C) time 13 coincidence types: ShortLongQuality 1aABCGold 2bABCGold 3abABCGold 4cABCPoor* 5acABCPoor* 6aABSilver 7bABSilver 8abABSilver 9aACSilver 10cACPoor* 11bBCSilver 12cBCSilver 13bcBCSilver * Highly unlikely that a trigger in CEM C in the short window is a valid ENA event

10 The IBEX-HI SensorVoyagers in the Heliosheath Conference, January 12, 2009 Event type probabilities: Triples Triple Coincidence Event Set CombinationEvent Probability Qualified aABC0.63 bABC0.14 abABC0.21 Unqualified c in short window 0.02 Event-type ratios can be used to distinguish signal from backgrounds

11 The IBEX-HI SensorVoyagers in the Heliosheath Conference, January 12, 2009 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 The IBEX-HI SensorVoyagers in the Heliosheath Conference, January 12, 2009 Penetrating Background Rates (Calibration) Measurement Background rate Singles CEM A89 mHz CEM B115 mHz CEM C69 mHz Background Monitor12 mHz Double Coincidences All AB2.8 mHz All BC4.2 mHz Qual(Not_C) AC0.13 mHz Triple Coincidences All ABC1.04 mHz Qual(Not_C) ABC0.58 mHz

13 The IBEX-HI SensorVoyagers in the Heliosheath Conference, January 12, 2009 Continuous Sampling of ENA Measurements vs. ecliptic latitude 7 days 14 days 1 month 6 months Best statistics at high latitudes Possibility of observing time variability in heliosheath/TS on time scales < 6 months?

14 The IBEX-HI SensorVoyagers in the Heliosheath Conference, January 12, 2009 Time Resolution of ENA Measurements Time uncertainty within energy passbands ( days) Time [days] Travel time to 100 AU Energy width of ESA passbands introduces uncertainty in ENA arrival time

15 The IBEX-HI SensorVoyagers in the Heliosheath Conference, January 12, 2009 Aspera/MEX Flux and Other Models of ENA Flux at 1 AU ENA flux predictions at a given energy range over ~5 decades!

16 The IBEX-HI SensorVoyagers in the Heliosheath Conference, January 12, 2009 Predicted IBEX Triple Coincidence Count Rates Detection Limit Increasing sensitivity with energy flattens steep flux distributions

17 The IBEX-HI SensorVoyagers in the Heliosheath Conference, January 12, 2009 IBEX HI Status Commissioning completing this week All systems operating nominally Detector gains as before launch Positive ENA detection: ━ Heliospheric ━ Magnetospheric

18 The IBEX-HI SensorVoyagers in the Heliosheath Conference, January 12, 2009 IBEX-HI is performing fantastically… Wait for it! Doubles (aAB) Triples (aABC, bABC, abABC)