Dim ENA Emissions from 1-30 keV D.J. McComas, P. Valek, J.L. Burch, and C.J. Pollock Southwest Research Institute San Antonio, TX H.O. Funsten, R.M. Skoug, M.F. Thomsen Los Alamos National Laboratory Los Alamos, NM Yosemite Meeting – 8 February 2002

Introduction/Outline Looking for dim ENA emissions requires careful attention to all MENA backgrounds Search for extended plasma sheet emissions Find extended emissions associated w/ SDPSs Find a remarkable background association w/ EPs Examine low background emissions for annual and directional asymmetries Discuss possible implications for heliospheric ENAs

MENA Sensor Head Design

Sources of Background Counts Coincident events –Energetic ions passing/scattering through collimator –Some penetrating radiation Non-coincident events –Solar and geocoronal UV (Ly-  & shorter) –MCP dark counts (typically ~1 cm -2 ) –Most penetrating radiation Electronic noise Electronic crosstalk

Culling MENA Backgrounds Only possible with complete information (“statistics data” or direct events) Remove unphysical events –Too short and negative times-of-flight –Too small pulse heights –Illegal locations (stops in starts, gutters, etc.) Correct high fluxes for under sampling –Not required for dim events examined here

Raw Culled Head 1 MENA/Imm Stats: June 10, 2000; 11:01:37-11:21:38 (10 spins)

Heads 1-3 MENA/Imm Stats: June 10, 2000; 11:01:37-11:21:38 (10 spins) Raw Culled

Studying Dim ENA emissions Achievable under locally quiet conditions –Not generally possible during storms –IMAGE at high altitude in Lobe Culling required to remove spurious points Must view away from bright emissions –Solar UV –Terrestrial scattered UV –Near-Earth ENA emissions

40-min Averaged MENA Images TypicalExtended PS

Borovsky et al., JGR, 103, r [ R ] E The Near-Earth Plasma Sheet

Borovsky et al., JGR, 103, 1998 “Superdense” Plasma Sheet

Superdense Plasma Sheet Intervals Identified in MPA data in Geosync 31 days over 8 months (Oct-May 2001) 13 intervals suitable for comparison –Low enough backgrounds –Descent viewing (seasonal and orbital) 11 of 13 show extended ENA emissions Several strong examples –Very low background and excellent viewing Extended PS ENA emissions clearly associated with superdense intervals SDPSs extend well beyond Geosync

GOES-8 Background Data GOES NOAA Geosync satellite Energetic Particle Sensor (EPS) data* Differential proton flux channel 700 keV – 4 MeV (penetrates collimator) May be tail of lower energy distribution May scatter in collimators and/or gratings Enter MENA through aperture Create correlated start/stop (“real”) events * Thanks to Terry Onsager and NOAA/SEC

April 2001

May 2001

MENA vs GOES

Day of year Counts per Spin Black = 2000 Red = 2001 Annual Variation of ENAs away from Earth

Coverage Uncorrected Corrected Spatial Variation of ENAs away from Earth - GCI latitude vs longitude apogee spins (of 530) - GOES < 5 / cm 2 s sr MeV - Holes at IMAGE Z-axis - Bright near solar apex (~271 ra, 30 dec)

Taken from Gruntman et al., JGR, 106, 2001 The Heliospheric interaction with the LISM

Penetration of ENAs into Inner HSp Gruntman et al., JGR, 106, 2001 McComas et al., GRL, 26, 1999

Models of HSp Interaction ENAs near 1 AU Gruntman et al., JGR, 106, 2001

Czechowski et al., ICRC 2001, 2001 ACR generated ENAs

Model Energy Distributions of ACR-ENAs Czechowski et al., ICRC 2001, 2001

Summary Able to examine dim ENA emissions by careful attention to various MENA backgrounds Found a remarkable background associated w/ GOES energetic protons Discovered quite distant plasma sheet emissions associated w/ “superdense plasma sheet” intervals –SDPSs extend well beyond Geosync Discovered annual and directional asymmetries in dim ENA emissions from ~1-30 kev that may be from heliospheric ENAs