SOPA Electron Data Revisited

1
SOPA Electron Data Revisited

• T. Cayton and M. Tuszewski, ISR-1
• Los Alamos National Laboratory
• (collaborators R. Belian, R. Christensen, R.
  Friedel, M. Henderson,
• J. Ingraham, M. Kippen, M. Thomsen)
• NASA Radiation Belt Workshop
• October 5-8, 2004

2
LANL GEO and GPS Charged Particle Data

• GEO (7 satellites since 1989)
• MPA (e and p 1 eV to 40 keV, 40 channels)
• SOPA (e 50 keV to 2 MeV, 10 channels, p 50 keV
  to 8 MeV, 12 channels)
• ESP (e 0.7 to 10 MeV, 6 channels, p 20 to 100
  MeV, 3 channels)
• GPS (4 satellites with CXD since 2001)
• LEP (e 0.14 to 2 MeV, 5 channels, p 6 to 50
  MeV, 2 channels)
• HXP (e 1 to 10 MeV, 6 channels, p 20 to 100
  MeV, 3 channels)

3
Energetic Charged Particle Data Analysis

• The omnidirectional counts (Ck, for each channel
  k, s-1) are related to the electron (e) and
  proton (p) differential fluxes (je(E) and jp(E))
  through responses (Gk(E) ) as

e ?
p contamination (gt 50 MeV side-penetration)

• Cek ?GeekjedE ?GepkjpdE
• Cpk ?GpekjedE ?GppkjpdE

p
e contamination (noise, backscattering, pile-up,
?,..)
4
Analysis of SOPA electron data(excludes SEP
events)

• Solve Cek ?GeekjedE (Cek corrected for cosmic
  background)
• Past Ck ?GdkjdE jdk?GdkdE ? jdk FkCk
  (Fk 1/?GdkdE)
• Present Ck ?(Gdk Gbk)jdE ? invert for j(E)

3-6 spacecraft
5
Bremsstrahlung test case

Cu
Si
Gb (cm2sr)
Integral responses
Al
E (MeV)
AP references NIM A 482 653 (2002), Space
Weather (to be published, 2004)
6
SOPA test case
Si
Cu
Al
G-10
Mg
7
SOPA detector electron responses
10
Gdk (cm2sr)
k 1
8
SOPA bremsstrahlung responses(detector box
satellite)
k 1
Gbk (cm2sr)
10
9
SOPA total electron responses
Gdk Gbk (cm2sr)
k 1
10
10
Preliminary SOPA electron data analysis(satellite
1989-046 only)

• Obtain jdk (k 1 to 10) from existing GEO merged
  data files
• Recover measured counts Ck jdk/Fk
• Model j(E) 2 Maxwellian PSD ? (4 adjustable
  parameters n1, T1, n2, T2)
• Calculate Cck ?(Gdk Gbk)j(E)dE for a given
  j(E)
• Find parameters (n1, T1, n2, T2) for best
  (least-square) fit of Cck to Ck
• Compare calculated spectra j and detector-only
  spectra jd

11
Qualitative Expectations
(1)
(2)
(3)
jd
j
E
12
06/07/90 (9.0 UT)
MPA
SOPA
jd
j
0.05
Ratio of bremsstrahlung to total counts in SOPA
channel 1
13
09/10/90 (22.2 UT)
0.37
14
04/16/90 (4.0 UT)
0.56
15
03/30/91 (2.0 UT)
0.93
16
03/29/91 (0.4 UT)
Cc Cd f?Cb
f 0
0.5
1
2
0.93
17
03/28/91 (13.3 UT)
0
0.5
1
0.31
0.93
2
18
Near-term GEO tasks

• Calculate electron responses for all GEO
  satellites
• Write efficient code to calculate j(E) for all
  times
• Calculate off-diagonal responses (Gep, Gpe)
• Calculate ESP responses

19
Summary

• New SOPA electron responses are obtained, that
  include bremsstrahlung photons
• Preliminary electron spectra are derived with the
  new responses
• (at selected times with negligible proton
  contamination)
• Bremsstrahlung effects are small for soft
  electron spectra
• Bremsstrahlung effects are important for hard
  electron spectra,
• (for such cases, one obtains a better spectral
  resolution, and a better match of the MPA and
  SOPA data)