The sidereal time variation of cosmic rays (median primary energy : 3 10 to the 15th power eV) is investigated with air shower observations at Akeno, Japan (900 m a.s.l.) which started in September 1981. Air showers are detected by a coincidence requirement on several muon detectors. The result obtained for three years is suggestive of a big semi-diurnal variation (0.37 % in amplitude). On the other hand, the diurnal variation is rather small than the semi-diurnal one. The feature of the sidereal anisotropy supposed from the present result looks quite different from that below 10 to the 14th power eV

Hayashida, N.

Kifune, T.

Murakami, K.

English

NASA Technical Reports Server

250
0C5.3-6
The sidereal anisotropy of cosmic rays around 3.1015 eV observed
at a middle north latitude.
K. Murakami
Cosmic Ray Research Laboratory, Nagoya University
Chikusa, Nagoya 4649 JAPAN
T. Kifune and N. Hayashida
Institute for Cosmic Ray Research, University of Tokyo
Tanashi, Tokyo 188, JAPAN
ABSTRACT
The sidereal time variation of cosmic rays (median primary
energy : 3.10 zs eV) is investigated with air shower observations
at Akeno, Japan (900 m a.s.l.) which started in September 1981.
Air showers are detected by a coincidence requirement on several
muon detectors. The result obtained for three years is suggestive
of a big semi-diurnal variation (0.37 % in amplitude). On the
other hand, the diurnal variation is rather small than the semi-
diurnal one. The feature of the sidereal anisotropy supposed
from the present result looks quite different from that below
i0 I_ eV.
1. Introduction. In Bangalore Conference (1983), a review on sidereal
anisotropies in air shower observations was given by Linsley (1). The
anisotropy beyond 10 I_ eV is still ambiguous, because of poor statistics
and also because most of results except that by Daudin et al. (2) are
not from air shower observations proper to the study of the sidereal
anisotropy. Recently we have carried out air shower observations at
Akeno, Japan (35°47'N, 138°30'E, 900 m a.s.1.) with the aim of studying
the sidereal anisotropy around 3.10 z5 eV.
2. Observations. The observations are made by using four much detec-
tors (25 m2, 50 proportional counters, 2 m thick concrete) being located
100_200 m apart from each other. The detection of air showers is done
by the following triggering requirements. Fifty proportional counters .
in each muon detector are divided into four groups of ten counters with
spacing of three counters. For detection of shower, at first, a coin-
cidence of incident particles is selected in the mode of "any two groups
out of four counter groups" in each muon detector, and next, another
coincidence is done in the mode of "any three- or four-fold coincidence"
among the coincidence signals fed from those four much detectors.
The response function was obtained from the analysis of air showers
(1844 events) detected by the above-mentioned conditions. The result
(normalized integral response function) is shown in Fig. 1, where solid
points and open circles are values derived via the determinations of
muon size and electron size, respectively. In this analysis the follow-
ingpointsarenoted.(1)The median primary energy is about 3.10 z5 eV.
(2) The zenith angle distribution of detected air showers per solid
angle is proportional to cos 5"2 8 (8 : zenith angle). (3) Although the *
present triggering was doubted if it was favoured for detecting much-
rich showers, no significant distinction from cases of electron trigger-
ing was found.
The continuous observations have been carried out since September
0 
OG 5.3-6 
 i ereal a isotropy f c s ic r s r d ' 15 eV s rved 
  ddle rth l titude. 
. a i 
os ic Ray esearch Laboratory, agoya niversity 
hikusa, agoya 464, JAPAN 
. ifune  . ashida 
Institute for os ic ay esearch, niversity of Tokyo 
nashi,Tok  , AN 
TRACT 
The sidereal ti e variation of cos ic rays ( edian primary 
e ergy: 3.10 15 e ) is i vestigated ith ir sho er servations 
at keno, Japan (900  a.s.l.) hich started in Septe ber 1981. 
ir sho ers are detected by a coincidence requirement on several 
muon detectors. The result obtained for three years is suggestive 
of a big se i-diurnal variation (0.37  in a plitude). On the 
ther d, e urnal ariation s ther ll t n t e i-
diurnal one. The feature of the sidereal anisotropy supposed 
fro  the present result looks quite different fro  that belo  
10 14 e 
. Introduction. I  angalore nference ( 983), a re iew  sidereal 
'~lnTs-()troples in air sho er observations as given by Linsley (1). The 
anisotropy beyond 10 14 e  is still a biguous, because of poor statistics 
a  also ecause st f results e cept t at by audin t l. ( ) are 
not fro  air sho er observations proper to the study of the sidereal 
isotropy. cently  e a ried t ir er servations t 
keno, Japan (35 047'N, 138 030'E, 900  .s.l.) ith the ai  of studying 
e idereal isotropy ound .10 15 a 
2. bservations. The observations are ade by using four uon detec-
tors (25 2 , 50 proportional counters, 2  thick concrete) being located 
0", 200  art  h ther.  etection' f ir ers s e 
by the following triggering requirements. Fifty proportional counters 
in each uon detector are divided into four groups of ten counters ith 
spacing f three counters. or etection f sho er, t first, a coin-
cidence of incident particles is selected in the mode of "any two groups 
out of four counter groups" in each muon detector, and next, another 
oincidence is e in the e f "any thr e- r four-fold oincidence" 
 the oincidence. ignals fed fro  those four on etectors. 
The response function was obtained from the analysis of air showers 
( 8 4 ents) etected  the bove-mentioned onditions. he esult 
(normalized integral response function) is shown in Fig. 1, where solid 
oints d pen ircles re alues erived ia the eterminations f 
uon size and electron size, respectively. In this analysis the follow-
ing-points are noted. (l) The edian primary energy is about 3.10 15 e e 
(2) The zenith angle distribution of detected air showers per solid 
angle is proportional to COS 5 •2 8 (8 : zenith angle). (3) Although the 
present triggering as doubted if it as favoured for detecting uon-
rich showers, no significant distinction from cases of electron trigger-
ing as found. 
The continuous observations have been carried out since September 
.. 
https://ntrs.nasa.gov/search.jsp?R=19850025759 2020-03-20T18:01:07+00:00Z
281
OG 5.3-6
1.0 i l _._.__'-'--T--
(electronsize) .f
_ 2.6 x 1015 eV,_,_ ;_
==°0.5 ..... o2 ......kl.
"0 •
_ ,o-_/ 2.7 x 1015 eV
o .._/ ( much size )
0 _
z"_ 0 -- I I
1015 1016 1017
Primary particle energy, eV
Fig. 1 Response function.
1981, In the following,
a result obtained for
three years until August o ht o hr
1984 is reported. The o.z z solarurn, o.z _.
number of events is, in f _AS _3
total, 2,2379059 showers
observed in 962 days, -18 _ t l
after the rejection of s_ , 6 9 : : s ' "'p
days in which complete
observations (with
stable operation under
12 6
constant condition
throughout the day)
were not fulfilled. 0 hr o hr
3. Results. Fig. 2 _0"2 _ Sidereal time 0.2 ,_f
shows harmonic vectors /AS _ p
'. in solar, sidereal and zs_"--_-_._ , t 6 9 , _ s , , 3s pa ti-sidereal time,
averaged over three-year i
data without correction
" for barometric pressure \-_
effect or so on. The ].z /
barometric pressure
effect is of - 0.19 -+ hr \
0.03 % per mb. Open o.2 _ Antl-sldereal time 0.2 _ _ ._r
circles, P, shown in the
figure are vectors _ s_expected from the baro- _8 : :/s _ r 6 9 ' / , J 3
metric pressure effect. L ; )
. The othe vectors, S, /
are variations of rate
of single-particle
incidences into four 12
muon detectors includ-
ing background radia-
Fig. 2 Harmonic vectors.
51 
OG -6 
1.Or----------,r---------------~----~~~~~--,_--_, 
... 
ra 
'"' c: 0\0 
G)..-i 
+"+" 
.=igo.s -7
f ~ ,0' ~ ~ ~ 3l 0/ 2.7 x 1015 eV 
';ti § .0-" ( muon size ) 
~ ~ ,<Y' 
o G) ,.0'- 0' z a: 0 '--__ ~~_ _'_ _________ _1_ ________ _'__ _ _.I 
ig. 1 
.  e lowing, 
 sult tained r 
three r  til st 
  ed.  
number of events is, in 
, , 37, 59 s 
ved  2  
t  th  r jection  
  ich pl te 
ions i h 
e ion  
 i ion 
t roug t t  a ) 
 t lled. 
. esult . i .  
shows harmonic vectors 
in solar, sidereal and 
ti idere l tim , 
  y r 
t  it  r ion 
for barometric pressure 
f t r  .  
barometric pressure 
effect is of - 0.19 ± 
.   er b. pe  
i  , s  i  t  
figure are vectors 
expected from the baro-
metric pressure effect. 
he t r ect r , , 
rc ariations f rate 
f ingle-particle 
i  i t  f  
uo  et t  i l
i  ba  r i
rimary article energy, eV 
es se f ction. 
o p 
o hr 
0.2 " 
2 
o hr 
0.2 " 
Solar time 
SIdereal time 
o hr 
 r 
0.2 " 
-+--';;7F'-f,~-+--+- & 9 -+_-+-...;.5...,... __ -+- 3 
12 
o hr 
0.2 " 
12 
i .  
p 
nti-sid real ti e 
& 
ar oni  ect r . 
t i c n  from s u r r o u n d i n g  c o n c r e t e .  The r e g r e s s i o n  c o e f f i c i e n t  t o  a i r  shower  
r a t e  i s a t  most  o f  a  f a c t o r  2,  and s o  t h e  v a r i a t i o n  r e l a t e d  w i t h  s i n g l e -  
p a r t i c l e  r a t e  is n e g l i g i b l e .  The e r r o r  circle a r o u n d  a i r  shower  r a t e  AS 
means t h e  s t a n d a r d  d e v i a t i o n  o f  mean a m p l i t u d e  d e r i v e d  from t h e  s c a t t e r  
o f  h o u r l y  v a l u e s .  T h i s  d e v i a t i o n  is  o f  0.1 % and a l m o s t  e q u a l  t o  t h a t  
e s t i m a t e d  from t o t a l  number of r e c o r d e d  a i r  showers .  The d o t t e d  circle 
will be e x p l a i n e d  i n  t h e  l a s t  pa ragraph .  
The r e s u l t s  a r e  summarized a s  f o l l o w s  : 
( 1 )  The s o l a r  d i u r n a l  v a r i a t i o n  is v e r y  s m a l l .  T h e r e  is,  however ,  a  d i s -  
c r e p a n c y  from t h e  v e c t o r  P e x p e c t e d  from b a r o m e t r i c  p r e s s u r e  e f f e c t .  
Main p a r t  o f  t h i s  d i s c r e p a n c y  may be i n t e r p r e t e d  a s  a t m o s p h e r i c  t empera-  
t u r e  e f f e c t .  
(2) The s o l a r  s e m i - d i u r n a l  v e c t o r  i s  n o t  i n c o n s i s t e n t  w i t h  t h e  b a r o m e t r i c  
p r e s s u r e  e f f e c t .  
( 3 )  The a m p l i t u d e  of s i d e r e a l  d i u r n a l  v a r i a t i o n  i s  a s  much a s  twice o f  
t h e  s t a n d a r d  d e v i a t i o n  and s o  t h e  e x i s t e n c e  o f  t h e  d i u r n a l  a n i s o t r o p y  
i s  s t i l l  hazy. 
( 4 )  The s e m i - d i u r n a l  v e c t o r  i n  s i d e r e a l  time i s  o f  0 .37 f 0.10 % and  
5.7 + 0.8 hour .  The e x i s t e n c e  o f  t h i s  v c c t o r  w i l l  b e  d i s c u s s e d  aga i r i  i n  
t h e  l a s t  pa ragraph .  
( 5 )  The d i u r n a l  a s  well a s  s e m i - d i u r n a l  v a r i a t i o n s  i n  a n t i - s i d e r e a l  time 
a r e  s m a l l .  
4. S i d e r e a l  s e m i - d i u r n a l  v a r i a t i o n .  A s  ment ioned  above ,  it seems t h a t  
a  b i g  s i d e r e a l  s e m i - d i u r n a l  v e c t o r  is e x i s t e n t .  F u r t h e r  a n a l y s e s  on t h i s  
a n i s o t r o p y  were made. One i s  t h e  monthly s h i f t  o f  s e m i - d i u r n a l  v e c t o r  on 
s o l a r  t i n e  c o o r d i n a t e ,  a s  shown i n  F i g .  3. E x c e p t  t h e  s h i f t  f rom (Feb. ,  
Aug.) t o  (Sep., Mar.), t h e  a n t i - c l o c k w i s e  t u r n i n g  o f  t h e  v e c t o r  w i t h  
month is  v e r y  s u g g e s t i v e  o f  t h e  e x i s t e n c e  o f  t h e  s i d e r e a l  a n i s o t r o p y .  
However, a n o t h e r  a n a l y s i s  shows 
t h a t  t h e  s i d e r e a l  v e c t o r  ob- 
t a i n e d  f c r  e a c h  h a l f - y e a r  i s  
r a t h e r  w i d e l y  d i s t r i b u t e d  than  Solar time 0 hr 
t h e  s c a t t e r  e x p e c t e d  f rom uncorrected 
s t a t i s t i c a l  f l u c t u a t i o n  o f  for P 3une 
h o u r l y  v a l u e s ,  a s  shown i n  
F i g .  4. The d o t t e d  circle i n  
F i g .  2 is  c o r r e s p o n d i n g  t o  
t h i s  wide d i s t r i b u t i o n  o f  t h e  
v e c t o r .  T h e r e f o r e ,  i n  o r d e r  
t o  c o n f i r m  t h e  e x i s t e n c e ,  i t  Mar. 
\.. . 
\ 
may b e  n e c e s s a r y  t o  w a i t  f o r  9 .  
more a c c u m u l a t i o n  o f  t h c  d a t a .  
A t  p r e s e n t  we have  n o  i d e a  t o  
i n t e r p r e t  why t h e  v c c t o r  
s c a t t e r s  s o  wide ly ,  a l t h o u g h  
\+c a r e  t r y i n g  t o  s e e k i n g  f o r  Oct. 
t h e  r e a s o n .  
5. Summary. The s i d e r e a l  6 
time v a r i a t i o n  a round  3-lo1' 
eV was i n v e s t i g a t e d  w i t h  a i r  
shower  o b s e r v a t i ~ n s  a t  Akeno F ig .  3  Monthly v e c t o r  o f  semi- 
which s t a r t e d  i n  September  d i u r n a l  v a r i a t i o n  i n  s o l a r  time. 
252 
OG 5.3-6 
de  r t .   
      
 li i l .    
   
 l s.     
 f  r . 
l   r . 
    ll s: 
I)  l  i l i ti   ll. 
      
H    
 
)  l  i i r l t  t i i t t it  t  t i  
     
        
 . 
  i l    ± 0  
 ±     e    n  
 t . 
)        l  
 ll. 
    
l   
.    i i l  
 im     . '     ., 
.)  p., ~l ),  is   
 i e    
   
   
 er  r  
~ b
 r   
i l tion 
    
    
.   
s   
   
 r   
   r 
 e 
t      
  e  
s   
we e i   i  r 
 
   
i   0 10 15 
   r 
r bservatien~ t  
 tarteci   
Solar time 
Uncorr t  
 
o hr 
 
t10 l   
l i   r 
1981. The r e s u l t  o b t a i n e d  Sidereal time hr 
f o r  t h r e e  y e a r s  g i v e s  a  b i g  Uncorrected f o r  
s e m i - d i u r n a l  v e c t o r  i n  s i d e -  pressure 
r e a l  time, 0.37 2 0.10 % and  
5.7 2 0.8 hour .  Al though 3 
we n e e d  t o  a c c u m u l a t e  more 
d a t a  i n  o r d e r  t o  c o n f i r m  t h e  
e x i s t e n c e ,  it i s  v e r y  i n t e r -  
e s t i n  g  t h a t  t h e  semi - d i u r n a l  
v e c t o r  seems b i g g e r  t h a n  t h e  
d i u r n a l  v e c t o r ,  because  t h e  
d i u r n a l  v e c t o r  h a s  been con- 
f i r m e d  t o  b e  b i q q e r  t h a n  t h e  
s e m i - d i u r n a l  v e c t o r  a t  n o r t h  
l a t i t u d e s  i n  t h e  r e g i o n  a : Sep. 1981 - Feb. 1982 
below l o i 4  eV. b : Mar. 1982 - Aug. 1982 c : Sep. 1982 - Feb. 1983 
Although t h e  above  semi- d : Mar. 1983 - Aug. 1983 
d i u r n a l  v e c t o r  was g i v e n  w i t h  e : Sep. 1983 - Feb. 1984 
t h e  s t a n d a r d  d e v i a t i o n  esti-  f : Mar. 1984 - Aug. 1984 
mated from t h e  f l u c t u a t i o n  M : Sep. 1981 - Auy. 1984 
o f  h o u r l y  v a l u e ,  i f  we con- 
s i d e r  t h e  wide  d i s t r i b u t i o n  F i g .  4 D i s t r i b u t i c n  of s i d e r e a l  
o f  t h e  v e c t o r  o b t a i n e d  f o r  s e m i - d i u r n a l  v e c t o r  f o r  e a c h  
e a c h  h a l f - y e a r ,  t h e  s t a t i s -  h a l f - y e a r .  
t i c  f o r  c o n f i r m i n g  i ts  
e x i s t e n c e  i s  still u n s u f f i c i e n t  (now t h e  s i g n i f i c a n c e  l e v e l  = 1 %). 
The b a r o m e t r i c  p r e s s u r e  e f f e c t  is e x p l a i n a b l e  m a i n l y  w i t h  l o n g i t u d i -  
n a l  development  o f  muon s i z e .  
6. Acknowledgement. The a u t h o r s  e x p r e s s  t h a n k s  t o  Mr. K. H o j i  i n  
I n s t i t u t e  f o r  Cosmic Ray R e s e a r c h ,  U n i v e r s i t y  o f  Tokyo and  Mrs. M. Hayase 
and Mr. S. S h i b a t a  i n  Cosmic Ray Research  L a b o r a t o r y  f o r  t h e i r  v a l u a b l e  
a s s i s t a n c e s .  The a u t h o r s  thank  Mr. S. Shimonaga i n  S h a r p  Co. f o r  h i s  
p r e c i o u s  s u g g e s t i o n  a n d  a s s i s t a n c e .  
R e f e r e n c e s .  
1. L i n s l e y  3. : Conf. P a p e r s  1 8 t h  ICRC, Banga lore ,  1 2 ,  1 3 5 ,  (1983) .  
2. Daudin 3. e t  a l .  : Nuovo Cimento,  3, 1017 ,  (1956r 
- 
• 
• 
1981. The result obtained 
for three years gives a big 
semi-diurnal vector in side-
real time, 0.37 ± 0.10 % and 
5.7 ± 0.8 hour. Although 
we need to accumulate more 
data in order to confirm the 
existence, it is very inter-
esting that the se i-diurnal 
vector seems bigger than the 
diurnal vector, because the 
diurnal vector has been con-
firmed to be bigger than the 
semi-diurnal vector at north 
latitudes in the region 
below 1014 eVe . 
Although the above semi-
diurnal vector was given with 
the standard deviation esti-
mated from the fluctuation 
of hourly value, if we con-
sider the wide distribution 
of the vector obtained for 
each half-year, the statis-
tic for confirming its 
253 
OG 5.3-6 
Sidereal time 
Uncorrected for 0 hr 
pressure 
0.1 
a : Sep. 1981 - Feb. 
b : Mar. 1982 - Aug. 
C : Sep. 1982 - Feb. 
d Mar. 1983 - Aug. 
e 
f 
M 
Sep.1983 - feb. 
Mar. 1984 - Aug. 
Sep. 1981 - Aug. 
1982 
1982 
1983 
1983 
1984 
1984 
1984 
Fig. 4 Distribution of sidereal 
semi-diurnal vector for each 
half-year. 
3 
existence is still unsufficient (now the significance level = 1 %). 
The barometric pressure effect is explainable mainly with longitudi-
nal development of muon size. 
6. Acknowledge ent. The authors express thanks to Mr. K. Hoji in 
Institute for Cosmic Ray Research, University of Tokyo and Mrs. M. Hayase 
and Mr. S. Shibata in Cosmic Ray Research Laboratory for their valuable 
assistances. The authors thank Mr. S. Shlmonaga in Sharp Co. for his 
precious suggestion and assistance • 
References. 
1. Linsley J. : Conf. Papers 18th ICRC, Bangalore, 12, 135, (1983). 
2. Daudin J. et a1. : Nuovo Cimento, l, 1017, (1956)7 


The sidereal anisotropy of cosmic rays around 3 x 10 (15) eV observed at a middle north latitude

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