The Earth's atmosphere is continually being bombarded by primary cosmic ray particles which are generally believed to be high-energy nuclei. The fact that the majority of cosmic ray primaries are charged particles and that space is permeated with random magnetic fields, means that the particles do not travel in straight lines. The arrival time distribution of EAS may also transfer some information about the primary particles. Actually, if the particles come to our Earth in a completely random process, the arrival time distribution of pairs of successive particles should fit an exponential law. The work reported here was arried out at Sydney University from May 1982 to January 1983. All the data are used to plot the arrival-time distribution of the events, that is, the distribution of time-separation between consecutive events on a 1 minute bin size. During this period more than 2300 showers were recorded. The results are discussed and compared with that of some other experiments

Sun, L.

English

NASA Technical Reports Server

258
0_5.5 -8
OBSERVATION OF ARRIVAL TIMES OF EAS
WITH ENERGIES _6 X I0 '& eV
SUN Luorul
Department of Physics,Zhengz_ou University, _hina.
I. Introduction
_he earth's atmosphere is continually being bombarded by primary
cosmic ray particles which are generally believed to be high-energy
nuclei. The fact that the majority of cosmic ray primaries are charged
particles and that space is permeated with randommagnetic fields,
means that the particles do not travel in straight lines. This makes
the identification of distant sources very difficult. Nevertheless,
studies of _he arrival time and direction distribution of cosmic rays
are still used to seek significant information on problems of their
origin. From the beginning of the 1950's to the middle of the 1960's
about 50 experiments were carried out to study the arrival directions
of EAS with energy range from about 10/_ to I0/reV. Limsley and
Watson _I_ summarised the results of these experiments and gave a
review at 15th Cosmic Ray Conferece.
On the other hand, the arrival time distribution of EAS may
also transfer some information about the primary particles. Actually,
if the particles come to our earth in a completely random process,
the arrival time distribution of pairs of successive particles should
fit an exponential law. This is derivable from Poisson's distribution.
Several groups _2,3_ have reported a non-random component in the
arrival times of EAS with E_IOP#eV, but others_4_ did not find it.
Ths work reported here was carried out at Sydney University
from May 1982 to January 1983. _he results are discussed and compared
with that of some other experiments.
2. Experiment System
This experiment work was carried out by using the Sydney
Small Air Shower Array. This sea level array has been described in
detail elsewhere_5_° The array is composed of four fast timing
scintillators arranged as a 25m_25m horizontal square with four
triggering scintillators in a 4mX4m square in the same plane as the
fast timing scintillators. The _riggering scin_illator square is close .
58 
BSERVATION F RRI AL I ES  S 
I  ERGIES ~ 6  1  14 e  
B uorui 
epartment of Physics,ZhengzAou niversity, China. 
1. t duction 
~  earth's at osphere is continually being bo barded by pri ary 
cos ic ray particles hich are generally believed to be high-energy 
uclei. he fact t at the ajority of cos ic ray pri aries are charged 
articles and t at space is per eated ith rando  magnetic fiel s, 
eans t at the articles do not tra el i  strai ht li es. his akes 
t  i entification f ist nt rces ery ifficult. evertheless, 
t ies f ~b  rri al ti e  ir cti n istri ution f s ic r s 
are till used t  seek si ificant i f r ation on proble s f t eir 
ri in. ro  t e eginning f t e 50's t  t e iddle f t e 60's 
about 50 experi ents ere carried out to study the arrival directions 
IIJ. 17 
r S ith e ergy ra e fro  a ut  t  1  e e insley a  
atson (1) summarised the results of these experiments and gave a 
revie  at 15th os ic ay onferece. 
On the other hand, the arrival ti e distribution of EAS ay 
also transfer so e inror ation about the pri ary particles. ctually, 
if the particles co e to our, earth i  a co pletely rando  process, 
t  rri al ti e i t i tion f airs f cessive arti les uld 
fit an exponential la . This is derivable fro  Poisson's distribution. 
Several groups (2,3' have report.ed a non-random component in the 
arrival times of EAS with E>10'l#eV, but others(4) did not find it. 
The work reported here was carried out at Sydney niversity 
fro  ay 1982 to January 1983. '1Ihe results are discussed and co pared 
ith t t f so e t er e peri ents. 
2. Experi ent Syste  
his experi ent ork as carrie  out by si  t e ydney 
S all ir Sho er rray. his sea level array has been described in 
detail elsewhere(5). The array is compo~ed of four fast timing 
scintillators arranged as a 25mX25m horizontal square ith four 
triggering sciritillators in a 4mX4m square in the same plane as the 
fast ti ing scintillators. ~ triggering scintillator square is close 
,. 
.. 
https://ntrs.nasa.gov/search.jsp?R=19850025761 2020-03-20T18:00:58+00:00Z
259
.... o_ 5.3 - e
but not at the centre of the fast timing square. Pulses from the
scintilla@ors are sent via fast rise time coaxial cables to the
recordin_ electronics which is in an air conditioned hut with the
triggering scintillators. The recording electronics uses NIM/CAMAC
System. A master trigger pulse is produced if three out of four of
the triggering scintillators receive shower particles. Showers are
analysed in a desk-top compuer which is employed to control the
recording system. The shower direction is found by a weighted least-
squares fit of a plane shower front to relative arrival tlme of each
detector. Then, using the maximum likelihood method to estimate the
shower size and core position. Finally, the celestial coordinates of
the incident direction of the event is found out. The rate of analysed
showers is 127 per day or one every 11.3 minutes on average. The tame
needed for the full analysis is about 30 seconds.
3. Analysis and results
The data discussed here were obtained in the period from May 27
in 1982 to January 12 in 1983 at the campus of Sydney University
(latitude 33°s). During this period more than 23000 showers were
recorded. The data are analy_ed in two different ways as follows.
>.
o
z
uJ
0
iiii,r
u.
SOQ
20 40 60
TIME SINS | MIN
Fig. 1 Cosmic ray a_ival time dls_ihutlon
Firstly, all the data are used to plot the arrival-time
distribution of the events, that is, the distribution of time-separation
t between consecutive events on a I minute bin size (Fig. I). The smooth
curve shows the expected exponential distribution of the arrival times
assuming thal the time of occurrence of the events is completely random:
n=l;e(e-kt,_ e-_tL )
where _. is %ks average number of events per unit time. As can be seen
259 
OG 5.3 - 8 
but not at the centre of the fast timing square. Pulses from the 
scintillatore are sent via fast rise time coaxial cables/to the 
recording .iectronics which is in an air conditioned hut with the 
tri gering scintilla·tors. The recording electronics uses NIM/CAMAC 
System. A master trigger pulse 1s produced if three out of four of 
the tri gering scintillators receive shower particles. Showers are 
analysed in a desk-top compuer which is employed to control the 
recording system. The shower direction is found by a weighted least-
squares fit of a plane shower front to relative arrival ti e of each 
detector. Then, using the maximum likelih od method to estimate the 
shower size and core position. Finally. the celestial c ordinates of 
the incident direction of the event is fouDd out. The rate of analysed 
showers is 127 per day or one every 1.3 minutes on average. The tiDe 
n eded for the full analy is is about 30 seconds. 
3. Analy is and results 
The data discussed here were obtained in the period fro  May 27 
in 1,82 to January 12 in 1983 at the campus of Sydney University 
(latitude 330 B). During this period more than 23000 showers were 
recorded. The data are analysed in two di ferent ways as follows. 
> o 
z 
W 
::J 
o 
W 
D: 
LL 
500 
o 20 40 60 
TIME BINS 1 MIN 
Fig. 1 Cosmic ray arrival ti e dlatrlbution 
Firstly, all the, data are used to plot the a rival-time 
distribution of the events, that is, the distribution of ti e-sep ration 
~ between consecutive events on a 1 minute bin size (Fig. 1). The smooth 
curve shows the expected expo ential distribution of the arrival ti es 
assuming that the ti e of o currence of the events is compl tely random: 
n-N-(e -\t, _ .-).tl) 
wh re ~ is tke average number of events per unit ti e. As can be s en 
260 O@ 5o_ - 8
from Fig. I, the observation data a_e compatible with random
expectation. After adding the estimated losses for the observation
data,no deviations are greater than 3(r. So that; no experimental
evidence for abnor_l behaviour in the inter shower arrival time
distribution has been found.
Then, the data are analysed with respect to the sidereal time
variation. Since the experiment was interrupted occasionally for
maintenance and by power failures, some allowances for this
interrupti_ wust be made before the analysing. After rejecting
certain numbers of events from those "over-exposure" time intervals,
the run time for every sidereal hour interval is unified. The data
are analysed by using the "random walk" harmonic method and the results
aEe$
the fractional amplitude r = (1.911.1) %,
the probability of observing an amplitude _ r p = 0.21,
the phase of maximum _ = 74°_ 33°•
To compare these results with that of the experiments summarised
in Ref. (I_, they are plotted together in Fig. 2 (after Kiraly st al
_6_). the value of p of the present experiment sits at the middle of
Fig. 2 (I), and the value of_ Just falls in _ gap of the old data
in Fig. 2 (2). If anything this confirms the isotropy of arrival
directions.
No No
-- [] present experiment
1._ 1:
o o 110 10
L 1 .L l ; h l h , ' ' ' ' I
0 0.5 1.0 0 180 360
P (_r) _/ (deg.)
(1) (2)
Fig. 2 Comparison of the present experiment wlth the data of Ref. (1,1.
The ordinates are the frequencies and the ciroles contain
the numbers of experimental sets contributing to the data
(excluding the present experiment).
The data are also tabulated on Mercator Projections and a serieg
of chi-squared tests is applied. The results are shown in Fig. 3. The
largest value of X_" for the tabulation is 57. The probability that X_ "
should have exceeded this value for one or more of eight independent
260 00 5.3 - 8 
from Fig. 1, the observation data are compatible with random 
expectation. After adding the estimated losses for the observation 
data,no deviations are greater than 3U. So tha~ no experimental 
evidence for abnormal behaviour,in the inter shower arrival time 
distribution has been found. 
Then, the data are analysed ith respect to the sidereal time 
variation. Since the experiment as interrupted occasionally for 
maintenance and by power fail res, so e allo ances for t is 
interruption .oat be made before the analysing. fter rejecting 
certain numbers f events fr  t ose "over-exposure" ti e i tervals. 
the run ti e for every sidereal hour interval is unified. The data 
are analysed by using the "random walk" harmonic method and the results 
MI 
the fractional a plitude r = (1.9±1.1) . 
the probability of observing an amplitude ~r p  0.21. 
the phase of maximum ~ _ 74°± 33°. 
To co pare these results ith that of the experi ents su marised 
in Ref. (1), they are plotted together in Fig. 2 (after Kiraly et al 
(6). the value of p of the present experiment sits at the middle or 
Fig. 2 (1), and the value of~ just falls in the gap or the old data 
in Fig. 2 (2). If anything this confirms the isotropy of' arrival 
i ti s. 
No, , 
~ present experiment 
15 5 
@ @ 
10  
5 5 
o~~~~~~~~~~~ 
0.5 
Fig. 2 
P (~r) 
(1 ) r (degJ (2  
Comparison of the present experiment with the data of Ref. 
. r i t s ar  th  freq ci s a  th  ci cl  c t i  
the nu bers of experi ental sets contributing to the data 
(excluding the present experiment). 
( ) • 
'l!  t  ar  als  tab lat,  on ercator Pr j ti s and. a series' 
of chi-squared tests is applied.. The results are shown in Fig. 3. The 
largest value of X2 for the tabulation is 57. The probability that X~ 
s uld h  e eded t is v lue f r on  or r  of ei ht, i pendent 
• 
Mercator Project ion of Celestial Sphere 
AVE X I  
Right Ascension 
Fig. 3 Cellular  division of Mercatos Projection of 
c e l e s t i a l  sphere f o r  171 64 showers. 
bands is 1%. Thus the chi-squared t e s t s  show no s ignif icant  evidence 
'of anisotropy i n  the tabulated distr ibutions.  
4. Acknowlegement 
The auther wishes t o  thank Prof. H. Messel, Prof. C. B. A. 
McCusker, Prof. M, M. Winn and Dr.  J. Ulrichs i n  Sydney University 
f o r  t h e i r  constructive suggestions and support. 
References 
1.  insl leg, 3 .  et al, Proc. 15th XCRC, Plovdiv, Vol. 12 (1977), 203. 
2, Bhat, C. L. e t  al, Nature, V288 (1980). 146. 
3. Badino, G. e t  a1  ,Lett. ~ 1 - h o v o  dimenti, V28 (1980). 93. 
4. Fegan, D. J. e t  al, Proc. 17th I C R C ,  Par is ,  Vol. 6 (1981)~ 296, 
5. Sun, L. e t  al ,  Nucl. Instr .  & Meth. , 223 (1984 )~  173. 
6. Kiraly, P. e t  a l ,  Rivista de l  Nuovo Cimento, 2 (1979 )~  1. 
261 
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Observation of arrival times of EAS with energies or = 6 x 10 (14) eV

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