# Presentation: 564943

## 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

## 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)

## 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

- Cek = GeekjedE + GepkjpdE
- Cpk = GpekjedE + GppkjpdE

- e + 

- p contamination (> 50 MeV side-penetration)

- e contamination (noise, backscattering, pile-up, ,..)

- p

## 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

## Bremsstrahlung test case

- E (MeV)

- Gb (cm2sr)

- Al

- Cu

- Si

- AP references: NIM A **482 **653 (2002), Space Weather (to be published, 2004)

- Integral responses

## SOPA test case

- Al

- Mg

- Cu

- Si

- G-10

## SOPA detector electron responses

- Gdk (cm2sr)

- k =1

- 10

## SOPA bremsstrahlung responses(detector + box + satellite)

- Gbk (cm2sr)

- k =1

- 10

##  SOPA total electron responses

- Gdk + Gbk (cm2sr)

- k =1

- 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

## Qualitative Expectations

- j

- jd

- E

- (1)

- (2)

- (3)

## 06/07/90 (9.0 UT)

- 0.05*

- MPA

- SOPA

- jd

- j

- * Ratio of bremsstrahlung to total counts in SOPA channel 1

## 09/10/90 (22.2 UT)

- 0.37

## 04/16/90 (4.0 UT)

- 0.56

## 03/30/91 (2.0 UT)

- 0.93

## 03/29/91 (0.4 UT)

- 0.93

- Cc = Cd +fCb

- f = 0

- 0.5

- 1

- 2

## 03/28/91 (13.3 UT)

- 0.93

- 0.31

- 0

- 0.5

- 1

- 2

## 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

## 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)