The February 16, 1984 (0900 UT) solar flare was very energetic and produced a variety of emissions. The X-ray and gamma ray continuum measurement, made aboard the International Cometary Explorer (ICE) and the Pioneer Venus Orbiter (PVO), are briefly described

Fenimore, E. E.

Kane, S. R.

Klebesadel, R. W.

Laros, J. G.

English

NASA Technical Reports Server

I a 
//v-72 c4-- 
7YJ5r X-RAY AND LOW ENERGY GAMMA-RAY OBSERVATIONS 
t'y OF THE 16 FEBRUARY 1984 SOLAR FLARE 
S. R. Kane 
Space Sciences Laboratory, University of California, Berkeley 
R.  W. Klebesadel, E. E. Fenimore, and J. G. Laros 
Los Alamos National Laboratory, Los Alamos, New Mezico 
The 16 February 1984 (0900 UT) flare was very energetic and produced a variety of emis- 
sions. A preliminary summary of the X-ray, gamma-ray, radio and energetic particle observations 
has been presented earlier (Kane, 1985; Kane and Urban,  1986). Here we present only a brief 
description of the X-ray and gamma-ray continuum measurements. Implications of these observa- 
tions with respect to the propagation and confinement of energetic electrons in the corona and the 
chromosphere have been discussed elsewhere (Kane et al., 1 9 8 7 ~ ) .  
The X-ray and low energy gamma-ray observations were made with instruments aboard the 
ICE (International Cometary Explorer, formerly ISEE3) and PVO (Pioneer Venus Orbiter) space- 
craft. The characteristics of the two instruments relevant to  solar flare measurements have been 
described elsewhere (Kane et al., 1982; 19876). The X-ray and low energy gamma-ray continuum 
spectrometer on ICE consists of two detectors: a xenon-filled proportional counter covering 4.8-14 
keV X-rays in 6 energy channels and a NaI(T1) scintillator covering 26 keV-3.2 MeV photons in 12 
energy channels. The time resolution is 0.5-4 seconds depending on photon energy. The PVO 
gamma-ray burst detector consists of CsI scintillators and covers 0.1-2 MeV photons in 4 energy 
channels. The time resolution is 0.5-8 seconds depending on the telemetry rate. 
The 16 February 1984 (0900 UT) flare was  probably located about 40' behind the west limb 
of the sun. A t  the time of the flare, ICE was located close to  the sun-earth line and about 0.01 AU 
away from the earth in the sunward direction. The optical flare was thus completely occulted from 
the view of the ICE instrument. On the other hand, the PVO spacecraft, which was orbiting the 
planet Venus, was located about 16" behind the west limb of the sun. The flare was therefore in 
https://ntrs.nasa.gov/search.jsp?R=19870014131 2020-03-20T10:29:50+00:00Z
2 
full view of the PVO instrument. 
Figure 1 shows the PVO and ICE observations. The soft X-ray measurements by GOES 
satellite are also presented for comparison. The PVO instrument detected a very intense burst of 
100 keV-2 MeV photons beginning at about 0857 UT. The burst profile has considerable structure 
and appears to be related primarily to the impulsive phase of the flare. The impulsive hard X-ray 
burst and the gradual soft X-ray burst associated with such an intense gamma-ray burst are also 
expected to  be very intense. However the ICE and GOES observations show that the impulsive 
hard X-ray burst was very weak and the gradual soft X-ray burst was undetectable, indicating 
that  the very bright parts of these sources were occulted from the view of the near-earth instru- 
ments. This is consistent with the location of the flare being f a r  behind the solar limb. It is 
interesting to  note that  the impulsive X-ray emission, as seen from the earth, could be detected 
down t o  about 8 in this flare. Also the ICE instrument detected the onset of high energy parti- 
cles as early as -0904:30 UT. This indicates that, at the sun, these particles were injected 
promptly at the foot of the spiral interplanetary magnetic field line passing through the earth. 
Acknowledgments: The research at Berkeley was supported by the National Aeronautics and Space 
Administration under contracts NAs5-376 and NAGS-393. The work at the Los Namos  National 
Laboratory was performed under the auspices of the U.S. Department of Energy. 
REFERENCES 
Kane, S .  R., Observations of the behind-the-limb solar flare on 16 February 1984 (4900  UT), 
STIP Symposium on Retrospective Analysis and Future Coordinated Intervals, Le Diablaret, 
June 10-12, Switzerland, 1985. 
Kane, S. R., Fenimore, E. E., Iilebesadel, R. IV., and Laros, J. G., Spatial structure of >loo keV 
X-ray sources in solar flares, Ap. J. Letters, 254, L53, 1982. 
Kane, S. R., and Urbarz, H. W., A preliminary summary of the observations of the 16 February 
1984 solar flare, STIP Syrnposium on Retrospective Analyses,  eds. M. A. Shea and D. F. 
Smart, 1986. 
3 
Kane, S. R., Klebesadel, R. w., Fenimore, E. E., and Laros, J. G., Impulsive hard X-ray source in 
the high corona, in preparation, 1987~ .  
Kane, S. R., Klebesadel, R. W., Fenimore, E. E., and Laros J. G., Directivity of 100 keV-1 MeV 
photon sources in solar flares, Ap. J., submitted, 19876. 
FIGURE CAPTIONS 
Figure 1. The hard X-ray and low energy gamma-ray continuum observations of the 16 February 
1984 solar flare made with the ICE and PVO spacecraft. The soft X-ray observations made with 
the GOES satellite are also shown. Note the intense photon flux observed by PVO. The flare was 
in full view of PVO which was located behind the west limb of the sun. However the chromos- 
pheric part of the X-ray source was occulted from the line of sight of ICE and GOES, resulting in 
a relatively small X-ray flux observed by these instruments. Also note the prompt onset of ener- 
getic particles in the vicinity of the earth detected by the ICE instrument. 
v) SOLAR X-RAYS 
162 16 FEB. 1984 
PARTICLES 
L 
GOES 
(FLUX 1)  
1-8 a 
0.5-4 a 
(FLUX x IO) 
I C E  
4.8-5.0 KeV 
(RATE x IO6) 
5.8-6.9 KeV 
( RATE x 105) 
6.9-9.7 KeV 
(RATE x lo4) 
9.7- I4 K e V  
(RATE x 103) 
26-43 K e V  
43-70 Ke V  
78-154 K e V  
154-398 Ke V  
(RATE x 0.01 ) 
(RATE x 7.0 ) 
(RATE x 0.7 1 
(RATE x 0.1 1 
PVO 
100- 250 K e V  
( RATE + 500 1 
250-500 KeV 
(RATE x 1 )  
500- 1000 K e V  
(RATE x 1 )  
1000 - 2000 K e V  
(RATE x 1 ) 
I 
1 1 1 1 1 1 1 1 1 1 1 1 1 1  
0855 0900 0905 0910 
UNIVERSAL TIME 


X-ray and low energy gamma-ray observations of the 16 February 1984 solar flare

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