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

http://mena.lanl.gov/plots/stats/en_az/1day/2000/2000-287.whitebg.png

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

http://mena.lanl.gov/plots/stats/en_az/1day/2000/2000-279.whitebg.png

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