Download - Dim ENA Emissions from 1-30 keV
Dim ENA Emissions from 1-30 keV
D.J. McComas, P. Valek, J.L. Burch, and C.J. PollockSouthwest Research Institute
San Antonio, TX
H.O. Funsten, R.M. Skoug, M.F. ThomsenLos 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
Typical Extended PS
Borovsky et al., JGR, 103, 1998
0 5 10 15 20 25r [R ]E
The Near-EarthPlasma 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-8 --- 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
Cou
nts p
er S
pin
Black = 2000 Red = 2001
Annual Variation of ENAs away from Earth
Coverage
Uncorrected
Corrected
Spatial Variationof ENAs away
from Earth
- GCI latitude vs longitude- 366 apogee spins (of 530)- GOES < 5 / cm2 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
