The fluxes and spectra of the flare electrons measured on board Venera-I3 and I4 space probes are compared with the parameters of the hard (E sub x approximately  55 keV) and thermal X-ray bursts. The electron flux amplitude has been found to correlate with flare importance in the thermal X-ray range (r approximately 0.8). The following two types of flare events have been found in the electron component of SCR. The electron flux increase is accompanied by a hard X-ray burst and the electron spectrum index in the approximately 25 to 200 keV energy range is gamma approximately 2 to 3. The electron flux increase is not accompanied by a hard X-ray burst and the electron spectrum is softer (Delta gamma approximately 0.7 to 1.0)

Daibog, E. I.

Kurt, V. G.

Logachev, Y. I.

Stolpovsky, V. G.

English

NASA Technical Reports Server

62 SB 1.2-11
TWO TYPES OF ELECTRON EVENTS IN SOLAR FLARES
E.I.Daibog, _.G.Kurt, Yu.l.Logachev, V.G.Stolpovsky
Instltute of Nuclear Physics, moscow State University,
Moscow I19899, USSR
Abstract. The fluxes and spectra of the flare electrons mea-
Sured on board _enera-13 and I4 space probes are compared
with the parameters of the hard (E_55 ke¥) and thermal X-
ray bursts. The electron flux amplitude has been found to
correlate with flare importance in the thermal X-ray range
( r _ 0.8). The following two types of flare events have been
found in the electron component of SCR. (I) The electron
flux increase is accompanied by a hard X-ray burst and the
electron spectrum index in the _ 25-200 keV energy ra_e is
~ 2-3. (2) The electron flux increase is not accompamAed by
_hardy 0.7-1.0).X-ray burst and the electron spectrum is softer
I. _ethod and statist&cs.
The fluxes and spectra of the 25-1500 key electrons and
55-100 key hard (Xh-) XW--rayswere systematically meastured
in I98I-I983 on board Venera-I3 and I@ /I-3/. 300 SCR events
were selected which could be considered as flare-induced.
Only the SCR events which could be identified, using H_ a_d
thermal X-rays, with the flares in the Sun's _estern hemis-
phere were selected in o_der to s_udy the relationships bet-
ween the flare electron fluxes injected to interplanetary
space and the X-rays. The events were only analysed where
the > 70 ke_ electrons were observed, for it is obvious that
the > 55 _eV X -rays are produced by the electrons with Ee>
Ex. Such events amount to I30; out of them only 67 were ac-
companied by the xh-bursts; in 65 cases such an accompaui-
ment was not detected. These sets of events will be hence-
forth designated eXtXh and eXtXh .
2. Distribution functions.
We constructed the size distributions of the number of
events with given parameter ¥: _(¥) =(I/_)(dN_¥), where N
is the number of events in a given set. The highest electron
fluxes ( Je ) and the amplitudes Jxt and JXhOf, respectively,
the Xt-andXh_ursts are used as ¥ . The functions f (Je),
f (Jxt), and f (Jxh) are shown in Fig.la,b,c where the cros-
ses and the dashed lines relate to the eXtXh set. From
Fig. I it is seen that, threughout the major part of the in-
terval of the amplitudes Je ,Jxt , and JXh the distribution
£unctions may be approximated by a power low with index a .
It is seen that (I) the distribution functions of various
parameters within the same set are alike and have similar
indices and (2) the distr_butio_l functions of the same pa_a-
meters within differemt sets are characterized by different
. We have _ i.2-I._ for eXtXh and _ _ 1.7-1.8 for eXtXh.
Thus, by using the additional indication (the accompar4ying
Xh-burst), we have obtained two sets of events in which the
62 SH I.2-I1 
TWO TYPES OF ELEOTRON EVENTS IN SOLAH FLARES 
E.I.Daibog, V.G.Kurt, Yu.I.Logachev, V.G.Stolpovsky 
Ins ~ ute of Nuclear Physics, Moscow S ate University, 
Moscow 11 899, USSR 
Abstract. The fluxes and spectra of the flare lectrons mea-
sured on board Venera-I3 and 14 space probes are compared 
with the p rameters of the hard (E+~55 keV) and thermal X-
ray bursts. Th  lectron flux ampl~tude has been found to 
correlate with flare importance in the thermal X-ray range 
(r ~ 0.8). The following two types o  flare vents have been 
found in the lectron component of SOR. (I) The lectron 
flux increase is accompanied by a hard X-ray burst and the 
lectron spect,rum index in the ....... 25-200 keV nergy range is 
'1 '" 2-3. (2) Th  lectron flux increase is not accompanied by 
a hard X-ray burst and the electron spectrum is softer 
(A '1'" 0.7-I.0). 
I. Method and statist~cs. 
The fluxes and spectra of the 25-1500 keY lectrons and 
55-IOO keV hard ( Xh-) X-r s were systematically measured 
in 1981-I983 on board Venera-I3 and 14 /I-3/. 300 SOR vents 
were selected which could be considered as flare-induced. 
Only the SCR vents which could be identified, using H cJ. and 
thermal X-rays, with the flares in the Sun's W stern hemis-
pb re w re s lected in order to study the relationships bet-
ween the flare lectron fluxes injected to interplanetary 
space and the X-rays. The vents were only nalysed where 
the> 70 keV lectrons were observed, for it is obvious that 
the> 55 keV X -rays are produced by the lectrons with Ee> 
Ex' Such vents amoun  to 130; out of them only 67 w re ac-
companied by the Xh -bursts f in 63 ca es such an accompani-
ment Was not detected. These sets of events will be hence-
forth deSignated e tXh and e tXh • 
2. Distribution funct;ons. 
We constructed the size distributions of the number of 
vents with given p rameter Y: f (Y) =(I/N) (dN/dY), where N 
is the number of vents in a given set. The highest lectron 
fluxes ( Je ) and the amplitudes JXt and JXhof, respectively, 
the Xt- andxh-bursts are used as Y • The functions f ( Je ), 
f (Jxt) , and f (JXh) are shown in Fig.la, b, c where the cros-
ses and the dashed lines relate to the e tXh set. From 
Fig. I it is seen that, throughou  the major part of the in-
terval of the amplitudes.Je ,JXt , and .JXh the distribution functions may be approximated by a power low with index d • 
It is seen that (I) the distribution functions of various 
p rameters within the same set are alike and have similar 
indices and (2) the distr~butioll fUllctions of tbe same p ra-
meters within differemt sets are ch racterized by diff rent 
~ • We have eX' "-' I. 2-1.4 for e tXh and ex ...... I. 7-I.8 for e tXh. 
Thus, by using the additional indication (the accompanying 
xh-burst), we have obtained two sets of vents in which the 
https://ntrs.nasa.gov/search.jsp?R=19850026433 2020-03-20T16:53:05+00:00Z
63 SH 1.2-1I
intensity distributions differ in slopes. This means that
two types of electron events are realized in SCR which cor-
respona to different conditions for particles acceleration
and leakage in solar flares. We think that the conventional
approach (see, for example, /4/) makes it difficult to dis-
criminate the types of flare events in SCR because in this
case the distribution function of the events of given para-
meter Is usually constructed, irrespectively of the rela-
tionships of these events to other parameters of flare ac-
tivity.
,_...,(_._.._)_ From Fig. I it is
xo_ _o-3_o-2xo-_o° seen th_at the eXtXh
-_ a) B) o) to-- eXtXh events hum-
*c0 I__,,F..' __) _+_, _' bet ratio increases
with amplitudes Je
. io-X: _: and Jxt and that,
":_ starting from cer-
_*°'2 _'_ _ amplitudes, only the
rain values of the
_ I°'s _T_ eXtXh events occur."'_ . This is understand-
x0-4 \ . {.x_h} able in terms of the
\ . {.x,,_,,} big flare syndrome
x°'5 _oO'xo' x'_-x°__x°4'= x°'V'x°'_'x°'S'J"+ /5/ according to
_..(c2...., o)-I '_h'_(_'2"°)-'which, as Uhe power
Fig. I of a flare rises,
the probability for the flare to be accompanied by the en-
tire spectrum of flare events rises also. However, two ty-
pes of the SCR events can hardly be accounted for only by
the difference in the power of parent flares. From Fig. I
it is seen that there exists the interval of the Je and Jxt
amplitudes where the SCR events of both types are realized.
The electron spectra
Fig. 2 shows the results of comparing between the dif_-
ferential electron energy spectra in the eXtXh and eXtXh
events. In the energy range Eo_ 25-210 key the electron
_spectra were approximated by
' . {o×_} a power law with exponent YA.
_, i __{o_×_} The values of Ye presented inFig.2 have been obtained by
5 I averaging over the number ofthe events of given type in
4 Je + _ Je ] . The dots relate
to the eXtXh events, andT
I+ _ the crosses to the eXtXhs events. According to Fig.2,
_ the eXtXh events differ from
the eXlXh events in the elec-
lO-I i0 101 102 108 tron spectrum slope (a _e
0.7-I 0) and in the dependen-
Je' cm'2sec-lster-1 @
ce of _e on Je. Nevertheless,
Fig. 2 the differences in the spec-
63 SH I. -II 
intensity d~stributions d~ffer in slopes. This means that 
two types of electron events are realized in SOR which cor-
respond to different cond~tions for particles acceleration 
and leakage in solar flares. We think that the conventional 
approach (see, for example, /4/) makes it difficult to dis-
cri inate the types of flare events in SOR because in this 
case t e d~stribution f nction f t e vents f gi en para-
eter ~s usually constructed, irrespectively of the rela-
tionships of these events to other parameters of flare ac-
tivity. 
8) 
Jxt ' erg(cm
2
.ecr1 
10-4 10-3 10-2 10-1 laD 
B) 0) 
From Fig. I it is 
seen that the e t h 
to- eXtXh events num-
ber ratio increases 
itb mpl~tudes  
 t  at, 
t rt  o  er-
t i  al es f t  
ampl~tudes, only the 
eXtXh events occur. 
his  nderstand-
• - {eXtllh} l   s f  
• - (eXtXh} 
10-5L---'-,.--.........,,_ ..... ---':+-~~'---:'::· -r--!:' :r--="-= i   e 
10 10-7 10 10- 10-4 / / according to 
Je , (em· .. e.t.rr' JXh' ..... (cm· .. er' which, as bhe power 
i . I of a flare rises, 
the probability for the flare to be acco panied by the en-
tire spectru  of flare events rises also. owever, t o ty-
pes of the S  events can hardly be accounted f r only by 
t  i e i  t  er  r nt l . r  ~  I 
it i  s  t t t r  ist  t  i t r al f t  J  a  J  
a plitudes here the SCR events of both types are realized. 
The electron spectra 
Fig. 2 sho s the results of co paring bet een the d1t-
ferential electron energy spectra in the eXtXh and eXtXh 
events. In the energy range Ee~25-2IO keV the electron 
ctr  er  r i ated  
a power law with exponent 1~ . 
The values of 1e presented ~n 
i .    t i   
averaging over the number of 
th  t    ty  i  
tile intensity interval [Je , J   t::.. ] •  t  r l t  
to th  e X  t , an  
the crosses to the eXtXh 
• - {eXtXh) 
- - {eXtXh} 
4 
S 
Fig. 2 
I 
e t . r i  to . , 
the X  e t   from 
the extx  e t  in til  e
IDS tro  spectrum slope (A 1 e ,....., 
0.7 1.0) an  in the d -
ce of '/ e. o  Je . evertheless, 
the difrere s in the spec-
64 ,SI-IT. P-TT
tral characteristics of electron fluxes cannot account in
all cases for the Xh-burst accompaniment of the SCR events.
It is easy to verify that the identical electron fluxes at
a_e _ 2 produce the quantum fluxes differing by a factor
of less than 3. In some cases, therefore, we must have seen
both an Xh-burst and a SCR electron event.
The most probable condition for the eXt_h events to be
realized consists in that the plasma density n in the ac-
celeration region is low and all the accelerated electrons
_r the majority of them, are ejected to interplanetary me-
.ium within a period smaller than the Coulomb loss time.
_he values of Je and _e from Figs. I and 2 were used to es-
timate the uRRer l_mit of the density for the eXtXh events:
< 5xI09-I0 i_ cm-_.
Correlations
The coincidence of the slopes of the distribution func-
tions of events fox the amplitudes of various parameters
(see Fig. I) ensues from the correlation between the elec-
tron events and X-ray bursts:This is confirmed by direct
calculations o2 the correlation coellicients between the in-
tensities of X-ray bursts and electron fluxes fro_ the cen-
tral and western flares, r ( IgJe , IgJxt ) _ 0.8 _-0.02 for
I47 events with the > 25 ke_ electrons and I30 events with
the > 70 ke_ electrons. Such value of rext means that (I)
the energy lost 2or SCR electron acceleration is approxima-
tely proportional to the flare energy because the energy re-
lease in the xt-range is proportional to the energy reali-
zed in the flare /_/ and (2) the xt-flux may be also a mea-
sure of the power of a SCR event. We have also obtained that
r ( IgJe , ISJXh)_ 0.69. Partly, this may be relevant to
the fact that the electron flux must be compared with the
total number of quanta or with energ_ release in a burst _ =
=JJxhdt rather than with the Jxh-burst amplitude, because
it is 6 that is proportional to the particle number in the
generation region of the Xh-rays in terms of the nonthermal
model. Fig. 3 shows the correlation between 6 and Je" It
is seen that the relationship bet-
' ., ween J_ and _ is nearly linear
• • and th[t the calculated rexhN 0,79 +-
_o_ 0.03. From this it follows that the
_ "" " effectiveness of electron leakage to
•. interplanetary medium is approxima-
mu 10 2 _ *
• "-' • rely constant irreespectively of
_ ".. -"" " flare intensity.
_._o: • • Considering the index of the Xh-
ray quantum spectrum 6 is _ _ and
. "" varies little with flare intensity,
_o° • • we obtain for the energy release
• and the particle number at the Xh-
.... ray source ns: ns = k(8 )S ,
,o_ _o' _o-_ _o_ where k(8 )_--I.3x IO@I at the thres-
"(_.....>"°'_'_ hold values E_ = 70 _eV and Ee 55
Fig. 3 keV in case o_ thic_ target or trap
84 bH T.?-TT 
tral characteristics of electron fluxes cannot account 1n 
all ca es for the Xh -burst accompaniment of the SOR vents. 
It is easy to verify that the identical lectron fluxes at 
Are ~ 2 produce the quantwn fluxes differing by a factor 
of less than 3. In some ca es, th refore, we must have seen 
both an xh-burst and a SCR electron event. 
The most pro able condition for the eXtXh vents to be 
realized consists in tha  the plasma density n in the ac-
c leration region is low and all the acc lerated lectrons 
~r the majority of them, are jected to interplanetary me-
~ium within a period smaller than the Ooulomb loss time. 
rhe values of .Ie and '( e from Figs. I and 2 w re u§..ed to es-
timate the Ulmer 'l mit of the density for the eXtXh vents: 
< 5xI09-I010 cm-~. 
Correlations 
The coincidence of the slopes of the distribution func-
tions of vents for the amplitudes of various p rameters (see Fig. I) ensues from the correlation between the lec-
tron vents and X-ray bur ts:This is confirmed by direct 
calculations of the correlation coefficients between the in-
tensities of X-ray bur ts and lectron fluxes frof the cen-
tral and western flares. r ( 19 Je , 19JXt) '" 0.8 - .02 for 
147 vents with the ~ 25 keV lectrons and 130 vents with 
the> 70 keV lectrons. Such value of r eXt means that (I) 
the nergy lost for SCR lectron acc leration is approxima-
tely pr portional to the flare nergy because the nergy re-
lease in the Xt-range is pr portional to the nergy reali-
zed in the flare 4/ and (2) the Xt - flux may be also a mea-
sure of the power of a SCR vent. We have also obtained that 
r ( 19 Je , 19 JXh) ~ 0.69. Partly, this may be r levan  to 
the fact tha  the lectron flux must be compared with the 
otal number of quanta or with nergJ r lease in a burst e = 
= f JXh dt rather than with the JXh -burst amplitude, because 
it is € that is pr portional to the particle number in the 
g neration region of the Xh-rays in terms of the onthermal 
model. Fig. 3 shows the correlation between 6 and J~. It 
is seen tha  the relationship oet-
ween Je and 6 is nearly linear 
.. 
. . 
.' 
. 
'... .~" 
'. . . 
... 
.. 
Fig. 3 
and tha  the calculated reXh ....... 0.79 :t. 
.03. From this it follows that the 
effectiv ness of lectron leakage to 
interplanetary medium is approxima-
tely constant irreespectively of 
flare intensity. 
Oonsidering the index of the Xh-
ray quantum spectrum 6 is "'" 4 and 
varies little with flare intensity, 
we obtain for the nergy r lease e 
and the particle number a  the Xh_ 
ray source ns: ns;; k( 8 ) € , 
where k(8 )~  x 1041 at the thres-
hold values E = 70 keV and Ee = 55 
keV in case or thick target or trap 
66 SH I.2-II
model /6/. Considering that s = bJe (see Fig. 3) and turn-
ing to the number of particles injected from the source,
ninj , we obtain the following relation between ns and
nin _ in terms of the diffusion model: n s = Anmj and
Am IO_.
Re£ezences
I. Daibog E.I. etal. Kosm issl., I983, v.21, P.574.
2. Daibog E.I. etal. Izv. Akad. Nauk SSSR,ser.fiz., I984,
v.gS, No.IX, p.2158.
3. Belyakov S.A. et sl. Kosm issl., 1984, v.22, p. 906
4. Hudson H.S. Sola_ P_47s. I978, v.57, p.237.
5. Kahler S.W., J. Geophys.Res., I982, v.87, p.3439.
6. Merlose D,B., Bzown J.C. Mon. Not. R.astr.Soc., I976J_
v.176, p.IS.
6& S  I. -l1 
tnodel / /. onsidering t at 8  Je (s  ig. ) a  t r -
ing to the number of particles injected from the source, 
ninj ,we obtain the following relation between ns and 
ninj in terms of the diffusion model: ns = A nmJ and 
A'::!. 03. 
eferences 
I. aibog .l. et ale Kos  issl., 1983, v.2I, p.574. 
2. aibog .I. et ale Izv. kad. auk SSSR,ser.fiz., 1984, 
v.48, o.II, p.2I58. 
3. alyakov S. . at ale Kos  issl., 1984, v.22, p.906 
. udson .S. olar bys. 1 78, . , . 7. 
,. ahler S. ., J. eopbys.Res., 1982, v.87, p.3439. 
6. erlose .B., ro n J.e. on. ot. .astr. oc., I9761tl 
.I? , .I,5. 


Two types of electron events in solar flares

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