The problem of high energy neutrons and gamma rays generation in the solar conditions is considered. It is shown that due to a peculiarity of generation and propagation of neutrons corresponding solar flares should be localized at high helio-longitudes

Kocharov, G. E.

Mandzhavidze, N. Z.

English

NASA Technical Reports Server

150
SH-I •4-8
HIGH ENERGY NEUTRON AND GAmMA-RADIATION GENERATED
DURING THE SOLAR FLARES
G.E.Kocharov, N.Z.Mandzhavidze
Ioffe Physico-Tecnical Institute Academy of Sciences of
the USSR, Leningrad, 194021,USSR
Problem of high energy neutrons and gamma rays
generation in the solar conditions is considered.
It is shown that due to a peculiarity of genera-
tion and propagation of neutrons corresponding
solar flares should be localized at high hello-
longitude s.
Solar neutrons have been detected only for two flares:
for June 21 1980 on board of the S_ satellite by Chupp et
al. [11and for June 3 1982 simultaneously in several experi-
ments by S_EI,2_, neutron monitorsC3,4,5 _ and registration
of protons of solar neutron decay origin 161 .
Experimental data allow to establish that energy spec-
tra of neutrons generated in a flare may be described as
power law in wide energy interval 50 to 1000 MeV with the
spectral indexes 3 and 3.5 for the flares 21.06.80 and
3.06.82 accordingly.
In contrast to J-lines which are formed by low energy
particles (10-30MeV)neutrons contain an information cn energy
spectra and angular distributions of accelerated particles
in wider energy interval. Calculations of charged-particle
energy spectra based on the observed neutron spectra have
been made by Ramaty et al. and by us _7-13_.Ramaty et al.
considered thick-target model and assumed that in the inter-
action region the distribution of accelerated particles is
isotropic.They have also assumed that after their production
the neutrons escape freely from the Sun.But because the neu-
trons have mean free paths comparable to the stopping range
of the protons which produce them,the protons should be
trapped magnetically in the region at column depths signifi-
cantly less than their ranges.It was shown that both f-line
and neutron experimental data might be explained if charged
particle spectrum is described by the Bessel function.
150 
SH-1.4-8 
HIGH ENERGY NEUTRON AND GAMMA-RADIATION GENERATED 
DURING THE SOLAR FLARES 
G.E.Kocharov, N.Z.Mandzhavidze 
Ioffe Physico-Tecnical Institute Academy of Sciences of 
the USSR, Leningrad, 194021,USSR 
Problem of high energy neutrons and ga ma rays 
generation in the solar conditions is considered. 
It is shown that due to a peculiarity of genera-
tion and propagation of neutrons corresponding 
solar flares should be localized at high helio-
longitudes. 
Solar neutrons have been detected only for two flares: 
for June 21 1980 on board of the SMM satellite by Chupp et 
ale [1J and for June 3 1982 simultaneously in several experi-
ments by SMM~,2J, neutron monitors[3,4,~ and registration 
of pr tons of solar neutron decay origin [6J • 
Experimental data allow to establish that energy spec-
tra of neutrons generated in a flare may be described as 
power law in wide energy interval 50 to 1000 MeV with the 
spectral indexes 3 and 3.5 for the flares 21.06.80 and 
3.06.82 accordingly. 
In contrast to Y-lines which are formed by low energy 
particles(10-JQ eV)neutrons contain an information an energy 
spectra and angular distributions of accelerated particles 
in wider energy interval. Calculations of charged-particle 
energy spectra based on the observed neutron spectra have 
been made by R maty et ale and by us [7-13].Ramaty et ale 
considered thick-target model and assumed that in the inter-
action region the distribution of accelerated particles is 
isotropic. They have also assumed that after their production 
the neutrons escape freely from the Sun. But because the neu-
trons have mean free paths comparable to the stopping range 
of the protons which produce them, the protons should be 
trapped magnetically in the region at column depths signifi-
cantly less than their ranges.It was shown that both Y-line 
and neutron experimental data might be explained if charged 
, 
particle spectrum is described by the Bessel function. 
https://ntrs.nasa.gov/search.jsp?R=19850026455 2020-03-20T17:03:03+00:00Z
15 1 SH-I. 4-8
In our calculations we tried to refuse the assumption
on magnetic trap and considered a beam configuration of ac-
celerated particles.In this case for any direction of beam
the flux of solar neutrons increases with an increase of a
flare heliolongitude.It can be easy shown for the beam di-
rected to the observer.Really,the thickness of matter tra-
versed by accelerated particles in the solar atmosphere into
Earth's direction for limb flare is higher than for disc
flare about (J_Re/2ho )I12 __ 30-100 times (ho -is the
scale height, Ro - is the solar radius). If the accelerated
particles move to the Sun the neutrons which are scattered
on 90° for the limb flare and on 180° for the disc flare are
detected.The probability of backscattering is less relative
to the scattering on 90°.However, as in this case nuclear re-
actions occur in deep regions of the solar atmosphere an ab-
sorption of neutrons may be essential.This effect was consi-
dered by us and it is shown that the limb retains an advan-
tage.
All calculations of neutron generation and their escape
from the Sun were made using Monte-Carlo method taking into
account the angular and energy characteristics of (PP) and
(pile)reactions which are the main source of high energy
(>50 MeV) neutrons.The beams with different angles relative
to solar radius were considered.Particle spectra were pre-
sented as power law with different spectral indexes. For
different heliolongitudes total yield of neutrons and their
energy spectrum have been calculated.Fig. I shows the depen-
dence of the fluxes of the neutrons (> 50 MeV) on flare he-
liolougitude for 3 cases. It is seen that for all cases the
neutron fluxes are decreased strongly from the limb to the
disk.If we consider the beam directed to the Sun the experi-
mental spectra for the flares 21.06.80 and 3.06.82 may be
explained if _p= 3-3.5 for Ep>100 MeV.In this c_se using
experimental figures for total flux of neutrons: 2.8-1028and
2.5.1029 we obtain for the total number of accelerated par-
ticles the following values: Np(>30)=7-1032 and 7,5"1033 ,
 SH-1.4-S 
I  ur calculations e t  t  r f se t  ass ption 
on agnetic trap and considered a bea  configuration of ac-
celerated particles.In this case for a~ direction of bea  
t   f lar eutrons i reases ith  i r se f  
flare heliolongitude.It can be easy sho n for the bea  di-
r ct d t  t  bserver.Really,the t i e s f atter t -
ersed y celerated articles i  t  lar at osphere i t  
arth's ir cti n r li  l  i  i her t  r i  
flare about (.:J[Re /.2 ho ) 1/2 ~ 30-100 times (h  - is the 
scale height, Ro - is the solar radius). If the accelerated 
articles ove to the Sun the neutrons hich are scattered 
 0 f r t e lim  fl r  a   0 f r t e is  fl r  r  
etecte . he robability f ackscattering i  l ss r l ti  
to the scattering on 900 . owever,as in this case nuclear re-
ti s cur i   r i s f t  l r t osphere  -
s r ti n f eutr ns ay be ssential. This ff ct as c nsi-
dered by us and it is sho n that the limb retains an advan-
tage. 
ll l lati ns f tr  erati n  t ir  
fro  the Sun ere ade using onte-Carlo ethod taking into 
account the angular and energy c aracteristics of (PP) and 
(pRe) reactions which are the ain source of high energy 
(>50 e ) neutrons. he bea s ith iffere t angles relati e 
t  l r i  er  nsidered.Particle ctr  er  r -
sented as po er law ith different spectral indexes. For 
different heliolongitudes total yield of neutrons and their 
energy spectrum have been calculated.Fig.1 shows the depen-
  h  u   h  t s   e )   -
liolongitude for 3 cases. It is seen that for all cases the 
tr  flu  r  r  tro l  fro  th  lim  t  th  
.   si er th  a  i t  to th   th  eri-
ental spectra for the flares 21.06.~0 and 3.06.~2 ay be 
explained if Yp = 3-3.5 for Ep>100 MeV.In this C:lse using 
experi ental figures for total flux of neutrons: 2.S·1028and 
. . 29 e t i  f r the t t l ber f l r t  r-
ticles the following values: N (>30)=1.1032 and 1,5.1033 , p 
15 2 SH-I. 4-8
4 'O
"?00
gO°
46 , ,,,,,,,.: ,.,,, , _ i cosO
0 Fig,I i'cos-8 Fig.2 J
Dependence of neutron fluxes on Dependence of g_a-ray
flare heliolongitude for the flux on flare heliolon-
beams with different angles re- gitude for beams with
lative to solar radius. 6 different angles rela-
te=0, _=3,5, N_(>3OMeV)=I0 tive to solar radius.
2._=90°. 3.Iso_ropic yield to
upper hemispher_ _p= 2.5,_
tlNp(>30 MeV)/I, 7 &r"1.5-10"", n -is number density in an interac
tion region.
accordingly.These figures are in good agreement with the to-
tal number of accelerated particles obtained by using_-line -
data (see [13]and references thereiu).So,supposing a beam
configuration it is possible to explain particle spectrum as
power law from 10 MeV to 1000 MeV _ith single spectral index.
Definitive conclusion can be made after obtaining of experi-
mental distribution on heliolongitude for flares with measu-
rable neutron fluxes.
Now we concern with the problem of high energy _-rays.
At the present time 14 solar flares with high-energy
( > 10 MeV) _-rays are registered [14].These events have a
strong solar limb preference with 13 of 14 occurring in fla-
res with a heliocentric angle >72 ° [14].
If high energy gamma-rays are generated by ultrarelatl-
-/ 6,S'l 
fOO 
152 
10 '--I-+--+---+--+--~--+-+--:l-__ o Fig. 1 1 eos8 
Dep d nce of neutron fluxes on flare heli longitude for the beams with diff rent angles re-lative to solar radius. 6 
1.0(=0, i;,=3,5, Np(>30MeV)=10 2.~=900. 3.Isotropic yield to uh~:(>~gmtr:~~h? ~~.§:~023, n is number density in an interac-tion region. 
zo 
5 
4 
" 
SH-1.4-8 
900 
COS (j 10~-+~~+-~~~j+---
Fig.2 
Dependence of gamma-ray flux on flare heliolon-
gitude for beams with different angles rela-
tive to solar radius. 
accordingly.These figures are in good agreement with the to-
tal number of accelerated particles obtained by usingt-line 
d ta (see [13) and r f rences therein).So / supposing a beam 
configuration it is possible to explain particle spectrum as 
power law from 10 MeV to 1000 MeV with single spectral index. 
Definitive conclusion can be made after obtaining of experi-
mental distribution on heliolongitude for flares with measu-
rable neutron fluxes. 
Now we concern with the problem of high en6rgy (-rays. 
At the pr sent time 14 solar flares with high-energy 
( > 10 MeV) (-rays are regist red [14] .Th se events have a 
strong solar limb preference with 13 of 14 occurring in fla-
res with a heliocentric angle >720 [14]. 
If high energy gamma-rays are generated by ultrarelat~-
15 $ SH-1.4-8
vistic electrons then the radiation is directed along of
electron velocity and above considered arguments are correct.
Let us consider the case when the source of high energy gam-
ma-rays are _°-mesons,which are generated in the same reac-
tions as energetic solar neutrons.
It is seen (Fig.2)that the dependence for _<90 ° is
weaker than for the neutrons.For tangent beams _n advantage
of limb is obvious.But in this case the flare should occur
in dense region n >_1013cm-3.Accordingto _14_all high energy
_-ray flares are characterized by fast impulses (_ 2s)whlch
is in favour of high density of interaction region. Tans we
cannot exclude a n_clearorigin of high energy _-rays.To made
a definitive conclusion on the source of high-energy _-rays
it is very important to measure an energy spectrum of gamma-
radiation.
References.
I. Chcpp E.L. et al.Astrophys.J.Letts.,1982,v.263,p.135.
2. Chupp 3.L. et al.Proc. 18-th ICRC,Bangalore,1983,v.4,p.97.
3. Efimov Yu.E. et el.,ibid. ,v. 13,p.240.
4. Debrunner H.et al. ,ibid.,v.4,p.75.
5. lucclN. et al.,1984,Preprlnt,IFSl,ltallo,N84-I.
6. Evenson P. et al.Astrophys.J.,1983,v.274,p.875.
7. Ramaty R. etal. Astrophys.J.,1983,v.273,p.L41.
8. Ramaty R. et al.,Solar Phys.,1983,v.86.
9. Limgenfelter R.E. et al.Proc.18-th IORO,Bangalore,1983,
V.4,p.I01.
10.Ramaty R.,Murthy R.J.,Proc.of the Plasma Astrophys.School
and Workshop,Varenna,1984,p.83.
11.Kocharov G.E.,Mandzhavldze N.Z.Izv.AN SSSR,ser.flz.,1984,
v.48,N.11,p.2212.
12.Kochm_ov G.3.,Mandzhavidze N.Z.,Pis'ma v Astron.Journ.,
1984,v.10,p.771.
13.KocharovG.E.,Proc.ofthe PlasmaAstrophys.Schooland
_orkshop, Varenna, 1984,p.65.
14.RiegerE. et al. Proc.18-thICRC,Ba_Ealore,1983,v.4,p.83,
paperpresentedat 164-thAAS Meeting,Baltimore,Nm_yland,
1984.
153 
vistic electrons then the radiation is directed along of 
electron velocity and above considered arguments are correct. 
Let us consider the case when the source of high energy gam-
ma-rays are Jr°-mesons,which are generated in the same reac-
tions as energetic solar neutrons. 
It is seen (Fig.2)that the dependence for ct<900 is 
weaker than for the neutrons.For tangent beams Ln advantage 
of li b is obvious. But in this case the flare should occur 
in dense region n ~1013cm-J.According to ~~ all high energy 
(-ray flares are characterized by fast impulses (~2s)which 
is in favour of high density of interaction region. Thus we 
cannot exclude a nuclear origin of high energy (-rays.To made 
a definitive conclusion on the source of high-energy (-rays 
it is very important to measure an energy spectrum of gamma-
radiation. 
References. 
1. Ch~pp E.L. et al.Astropbys.J.Letts.,1982,v.263,p.135. 
2. Ch~pp E.L. et al.Proc.18-th ICRC,Bangalore,1983,v.4,p.97. 
3. Bfimov Y~.E. et al.,lbld.,V.13,p.240. 
4. Debrunner H.et al.,lbld.,v.4,p.75. 
5. I~eel 5. et al.,1984,Preprlnt,IPSI,Itall0,N 84-1. 
6. Evenson P. et al.Astrophys.J.,1983,v.274,p.875. 
7. Ramaty R. et ale Astropbys.J.,1983,v.273,p.L41. 
8. Ramaty R. et al.,Solar Pbys.,1983,v.86. 
9. Lingenfelter R.E. et al.Proe.18-th ICRC,Bangalore,1983, 
v.4,p.101. 
10.Ramaty R.,Murthy R.J.,Proe.of the Plasma Astrophys.School 
and Workshop,Varenna,1984,p.83. 
11.Koeharov G.B.,Kandzhavldze N.Z.lzv.AN SSSR,ser.f1z.,1984, 
v.48,N.11,p.2212. 
12.Koeharov G.E.,Kandzhavldze N.Z.,Pls t ma v Astron.Jo~rn., 
1984,v.10,p.771. 
13.Koeharov G.B.,Proe.of the Plasma Astrophys.Sehool and 
Workshop,Varenna,1984,p.65. 
14.R1eger E. et ale Proc.18-th ICRC,Bangalore,1983,v.4,p.83, 
paper presented at 164-th AAS Yeetlng,Baltimore,Maryland, 
1984. 


High energy neutron and gamma-radiation generated during the solar flares

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