The Haverah Park air-shower experiment recorded over 8500 events with primary energy  10 to the 18th power eV between 1963 and 1983. An analysis of these events for anisotropies in celestial and galactic coordinates is reported. No very striking anisotropies are observed

Eames, P. V.

Lloyd-Evans, J.

Morello, C.

Reid, R. J. O.

Watson, A. A.

English

NASA Technical Reports Server

2 5 4 OG 5.3-7
ARRIVAL DIRECTION DISTRIBUTION OF COSMIC RAYS OF ENERGY > iO 18 eV
P.V.J. Eames, J. Lloyd-Evans t, C. Morello *t, R.J.O. Reid and A.A. Watson
Department of Physics, University of Leeds, LEEDS 2, UK.
t Now at NASA/Goddard Space Flight Centre, USA.
_# Permanent address: CNR, Istituto di Cosmo-Geofisica, Torino,
Italy.
ABSTRACT
The Haverah Park air-shower experiment recorded over 8500 events
with primary energy > iO Is eV between 1963 and 1983. An analysis
of these events for anisotropies in celestial and galactic co-
ordinates is reported. No very striking anisotropies are observed.
i. Introduction. Seven years ago the Haverah Park group (Edge et al
1978) published a detailed analysis of the arrival direction distribution
of cosmic rays above 6 xlO I_ eV. Since that publication there have been
numerous 'up-dates' reported in conference proceedings and reviews. In
this report we concentrate on the cosmic rays above IO 18 eV where
additional running has enabled us to increase our data from 4202 events
(Edge et al 1978) to 8565. The additional data have been recorded with
the same angular resolution as in the earlier work (rms variation in solid
angle < iO-2sr); the energy resolution has been slightly improved by the
addition of 3x2.25m 2 detectors at 1 km from the array centre. We
describe here the results of an analysis in celestial and galactic co-
ordinates; fuller details will be reported elsewhere.
2. Harmonic Analysis in Right Ascension. The results of an harmonic
analysis in right ascension over the declination range 90<_ <-6 ° are
given as a function of energy in Table I. Following our previous
practice the data are divided in energy I- 2 x1018 eV (E5),
2-4 xlO is eV (E6), 4- 32 xlO Is eV (E7,8,9) and >3.2 xlO 19 eV (EIO). For
brevity the notation E5 etc. will be used here. The first and second
harmonics are given. Only amplitude uncertainties are quoted;
probabilities of tb_se amplitudes arising by chance from a random z
distribution equal exp(-ko) and the phase uncertainty is 57.3/(2ko) _
degrees, where ko = r2n/4 (Linsley 1975).
Table 1
from Edge et al (1978) Present Work
n rl% @i° ko n ri% elO k o
E5 2832 6.3 ± 2.7 50 2.83 5764 4.4 ± 1.9 67 2.76
E6 978 7.9 ±4.5 37 1.52 1939 3.7 ± 3.2 17 0.65
E7,8,9 364 7.9 ± 7.4 280 0.55 812 5.7 ±5.0 272 0.66
EIO 28 57 ±27 163 2.27 50 42 ±20 179 2.16
r2% 82 ° rz% 82°
E5 2832 3.0 ±2.7 169 0.64 5764 2.7 ± 1.9 175 I.O1
E6 978 ii ±5 71 2.74 1939 4.3 ±3.2 80 0.89
E7,8,9 364 18 ± 7 75 2.95 812 13 ±5.0 83 3.59
EIO 28 25 ±27 59 0.45 50 12 ±20 166 0.18
254  . -  
RI AL I TION I I UTION  S IC   RGY  10 18  
t tt . .J. es,  loyd-Evans  . orello , . . . ei   . . atson 
epartment f ysics, niversity  eeds, S , . 
t o  at ASA/Goddard Space li ht entre, S . 
tt Per anent address: CNR, Istituto di Cosmo-Geofisica, Torino, 
It l . 
ACT 
e averah ark i wer eri ent rded er 00 ents 
ith pri ary energy> 10 18 eV between 1963 and 1983. An analysis 
of these events for anisotropies in celestial and galactic co-
r inates i  r orted. o r  tri i g isotropies r  served. 
1. I tr duction. Seven ears ago the averah ark group ( dge t al 
8) blished a etailed alysis f t  rri al ir ction i tri ution 
of cos ic rays above 6xl016 e . Since that publication there have been 
nu erous ' -dates' re orted i  c nference r ceedings and re ie s. I  
t i  ort e ncentrate  t  s ic r s ve 10 18  here 
ditional ning s abled   rease r ata  2 ents 
ge t l 8)  65. e ditional ata ve een orded ith 
t e sa e a gular r solution as i  t e rlier ork (r s ariation i  s lid 
angle < 10- 2 sr); the energy resolution has been slightly i proved by the 
dition f x2.25m2 etectors t lk  fro  t e rr  ntre. e 
escribe ere t  r sults f  alysis i  lestial d alactic -
ordinates; f ller details ill be reported else here. 
. armonic nalysis  ight scension. e sults f  r onic 
alysis i  ri t s ension er t  eclination ra ge  < 8  -6 0 r  
given as a function of energy in Table 1. Following our previous 
practice the data are divided in energy 1- 2 x lOIS eV (E5), 
-4 l0 18 e  ( 6), - l0 18 e  ( 7,8,9) d 3.2 l Ig e ( l ). or 
revity  otation 5 t . i l e s d ere. he st  nd 
har onics are given. nly a plitude uncertainties are quoted; 
probabilities of tl\~se amplitudes arising by chance from a random I 
distribution equal exp(-ko) and the phase uncertainty is 57.3/(2ko)2 
degrees, here ko  r 2n/4 ( insley 1975). 
able  
fr  dge t al ( 78) resent ork 
n r1% e 0 1 ko n r 1% e 0 1 ko 
5 32 .3  0 . 3 64 .4 .   . 6 
6 8 .9 4.5  . 52 39 .7 .   . 5 
7,8,9 4 .   .  0 . 5 2 .7 5.0  . 6 
l  28   27 3 . 7    20 9 . 6 
r 2 % e 0 2 r 2 % e 0 2 
5 32 .0 2.7 9 . 4 764 .7 .  5 1.01 
6 78 11  5 71 . 4 39 .3 3.2 0 . 9 
7,8,9 4     . 5 12   5.0  . 9 
I  28   27 9 . 5 0 2  20 66 . 8 
https://ntrs.nasa.gov/search.jsp?R=19850025760 2020-03-20T18:00:54+00:00Z
2SS OG 5.3-7
It is disappointing to report that the doubling of the Haverah Park data
has led to a decrease in all of the amplitudes above i0 Is eV. Of the
8 amplitudes listed the significance, as measured by ko, of only 3 have
increased. However the most significant amplitude of the new set was
also the most significant of the original set: the 2nd harmonic in the
energy bin E7,8,9 now has a probability of arising by chance of 2.8%.
For 371 events in a similar energy range (5xlO Is-4xlO Ig eV) the
Yakutsk group find r2 = 7.6 ± 7.3% at e = 114 ° (Efimov et al 1983). The
joint amplitude (n = 1183) is r2 = II ±4%, 0 = 89° with a chance
probability of 2.8%.
The probability that the observed sets of 8 ko's arise by chance from a
random distribution has risen from 3% to 10%.
3. Analysis in Galactic Co-ordinates. In 1981 we introduced an analysis
in galactic latitude from which a series of gradients of observed number/
expected number as a function of galactic latitude was obtained (Astley
et al 1981). The initial analysis was with a data base intermediate in
size between that discussed in Edge et al (1978) and that now available;
a S-N assymetry was claimed. The gradients given by Lloyd-Evans and
Watson (1982) are listed together with the new gradients in Table 2. A
correction to the binning algorithm used in calculating the gradients has
been made and about 25% more data has been added above i0 Is eV. The
gradients are compared with results from other experiments in Figure I.
The Haverah Park gradients !
show deviations from expecta- ILI Figurel
tion significant at the 4%
level (X_ = 1.97) and in D50
addition (ignoring the most • HaverahPark
o Yakufsk
energetic (extragalactic?) 4 _ CorneU
events in EIO) there is a s VolcanoRanch
clear tendency for the 3
gradients to fall and then (.)
change sign as the energy 2 I
increases. However there are
• strong systematic differences
between the various experi- _ I
ments, none of which are
consistent with the above x 0 0
J
gradients, for which no
satisfactory explanation has _ I
yet been found.
2
4. Discussion. Wdowczyk
and Wolfendale (1984) ±nan 3
interesting discussion of (-)
cosmic ray anisotropy have
suggested that the observa-
tion of an S-N gradient 5
above IO is eV is an
artefact arising from the 6
limited galactic latitude
coverage of the Northern ?
Hemisphere experiments.
1oI  o2O v
• 
55 OG 5.3-7 
It is isa pointing t  r port t at t e oubling of t e averah ark data 
has l d t  a decrease i  l of t e a plitudes above 10 18 eV. Of t e 
8 amplitudes li ted t e si nificance, as easured by ko , of only 3 have 
i creased. ow ver t e ost significant amplitude of t e ne  set as 
lso t e ost i nificant f t e riginal set: t e nd armonic i  t e 
energy in 7,8,9 no  as a probability of arising by chance of 2. . 
or 371 events i  a si ilar energy range (  x 10 18 - 4 X 10 19 e ) t e 
akutsk group fi d r  = 7.6 ± .  at   140 ( fi ov t l 1983). The 
joint a plitude (  = 183) i  r 2 = 11  4%, e = 9 0 ith a chance 
probability of 2. . 
he probability t at t e observed sets of 8 o's arise by chance fr  a 
random distribution has risen fro  3% to 10 . 
3. na.ly is i  alactic o-ordinates. In 981 e i tr duced an analy is 
i  alactic l tit de fr  which a series of radients f observed number/ 
expected number as a f nction of galactic latitude as obtained ( stley 
t al 1981). The i itial analy is as ith a data base i termediate i  
size bet en t at discussed i  Edge et l ( 978) and t at no  available; 
a S-  assymetry as clai ed. The radients given by loyd-Evans and 
atson ( 982) are li ted t gether ith t e ne  gradients i  Table 2.  
co rection t  t e bi ning algorithm used in calculating t e radients has 
been ade and about 25  ore data has been a ded above 10 18 e . The 
gradients are compared ith resul~s 
The averah ark radients 
show deviations from expecta-
ti n significant t t e 4  
l vel (X~ = .97) and in 
a dition (i noring t e ost 
energ t c (extragalactic?) 
events in ElO) there is a 
clear t ndency f r t e 
gradients to fall and then 
change sign as the energy 
i creases. owever t ere are 
str ng systematic di ferences 
between t e various experi-
ents, none of which are 
consistent ith the above 
gradients, for which no 
satisfactory explanation has 
yet b en found. 
4. iscussion. dowczyk 
and olfendale (1984) in an 
i teresting discussion of 
cosmic ray anisotropy have 
su gested t at the observa-
ti n of an S-  gradient 
above 10 18 e  is an 
artefact arising fr  the 
li ited galactic latitude 
coverage of the Northern 
Hemisphere experiments. 
8 
6 
4 
3 
(+) 
2 
" 0 
+-
c 
'" ~ 1 
'-
l:J 
2 
3 
( ) 
4 
5 
6 
l-
r 
f-
r-
• 
r 
f0-
r 
r 
-
7f-
fr  other experiments in Figure 1. 
Figure 1 
-
SO . 
-
• Haverah Park 
0 Yakutsk 
6- Cornell 
G Volcano Ranch 
f -
+ 
f"' t 612 f764 1939 o 
t ~ 
-
I I I I 
256 OG 5.3-7
Table 2
Energy
interval Lloyd-Evans & Watson (1982) Present Work
gradient gradient
n (x 104 deg -I) n (x 104 deg -z)
E1 18829 -1 + 3 18829 3.9+2.4
E2 39982 - 2 + 2 39982 3.2 + 1.6
E3 20635 - 4 + 3 20635 O.7 +2.2
E4 5938 -8.5 +4.3 5938 -3.6 +4.1
E5 4349 -13 -+ 5 5764 -9.2 +4.1
E6 1499 -16 + 9 1939 -7.5 +7.O
E7,8,9 610 -22 +13 812 -3.3 +IO
EIO 38 92 +85 50 66 +47
They propose instead that the data should be tested against a model which
invokes a galactic plane excess and which predicts that the angular width
of the galactic plane as seen in cosmic rays should shrink slowly with
increasing energy.
The prediction of this model in which it is suggested that
I(b) = I(O) [(l-fE)+fE exp(-b2)]
is compared with the data in Figure 2 for fE, the galactic latitude en-
hancement factor, = 0.3 (Wdowczyk and Wolfendale 1985, Figure l(d)).
There is some evidence for a galactic plane enhancement.
We have investigated the
galactic plane enhancement
directly by comparing the 1.5-
nu_er of events within Figure2 E_8,?
_±5 ° of the galactic plane I"_i- N=812
for the declination range 12 £urve:Wd0wczykand W0[fendaLe(198_)
1"361.6 < _ < -6°. For bins Gradien_.......(3.3±I0)xI__
E5, E6, E7,8,9 the
observed number of events _ J _ _ ___
was 268, 93 and 36 while 21"I I *250, 83 and 36 were
expected. There is
clearly no significant _1'01 ---_ _evidence of enhancement. _0.9
In Figure 3 we compare
the first harmonics of _8- .
Table 1 with the pre- T
dictions of Hill and 0-7- I
Schramm (1985). The best b
estimate of the amplitude, 06- b---
, I _o I I I Is (Linsley 1975) is sho_ _° -50" - -_0° I_ 30' _ 7_ otogether with 95% and 5%
confidence levels. The
predictions are derived from a model in which cosmological and bright
56 OC 5.3-7 
able  
nergy 
i t rval l d-Evans  atson ( ) r sent ork 
n 
gradient 
n 
radient 
(xlO lf deg- 1) (x 10'1 deg -1) 
l  1 ±  9  ± 2.4 
 2 -  ±  2 . ±  
 35  ±  5 0. ± .2 
 8 . ± .3 8 .6±4.l 
   ±  4 .  ± 4.1 
   ±  9 . ± .0 
7,8,9   ±13  .  ± 10 
l    ± 85   ± 47 
hey propose i stead t at the data should be tested a ainst a odel hich 
invokes a galactic plane excess and hich predicts that the angular idth 
f t e alactic plane as seen i  cos ic rays should s ri k slo ly ith 
i reasing ergy. 
he rediction f t i  odel i  hich it i  s gested t t 
I(b) = 1(0) (1- f E) + fE exp (-b 2 ») 
is compared with the data in Figure 2 for fE' the galactic latitude en-
ancement f ctor,  .  ( dowczyk  olfendale 85, i ure l ». 
here i  s e i ence f r  alactic l ne ancement. 
e have i estigated t e 
alactic l ne ancement 
irectly  paring t  
mber f ents ithin 
a ± 50 f t e alactic l ne 
for the declination range 
1.6  0  - 0 • or ins 
5, 6, 7,8,9  
observed number of events 
was 268, 93 and 36 while 
50,  d  ere 
xpected. here  
clearly no significant 
evidence of enhancement. 
I  igure  e o pare 
the first har onics of 
Table 1 ith the pre-
dictions of Hill and 
chra m ( 985). he est 
estimate of the amplitude, 
s, (Lins ley 1975) is shown 
t gether ith 9  and 5  
confidence els. he 
'·5 
-2 
~1.1 
u QJ 
n. 
~1'0 
(}8 
0·7 -
0'6 
----
-70 -50' 
Figure 2 E7,8,9 
= 812 
Curve: Wdowczyk and Wolfendale (1984) 
'rod;"" •...• "·{J·lt lOJ, '0f 
- --
-30 70 
predictions are derived from a model in which cosmological and bright 
Acknowledgement. We thank John Lins ley f o r  a l lowing us t o  p resen t  h i s  
d a t a  i n  t h e  form shown i n  Figure  1.  CM thanks NATO f o r  a r e sea rch  
l o c a l  e x t r a g a l a c t i c  source  f luxes  
a r e  combined. The i n j e c t i o n  
spectrum s lope  y = 2.0 favoured 
fe l lowship  whi le  t h e  suppor t  of SERC t o  work a t  Haverah Park i s  g ra te -  
f u l l y  acknowledged. 
through t h e i r  f i t  of spectrum 100 
d a t a  p r e d i c t s  r a t h e r  h igher  
a n i s o t r o p i e s  above 5 x ~ o ' % v  
than  a r e  observed. 
5. Conclusion. H i  h energy $. 
References 
y =1.8 
y=2.2 
S M Ast ley  e t  a 1  1981 Proc. 17th  I C R C  ( P a r i s )  2, 156. 
- 
D M Edge e t ' a l  1978 J Phys G 4,  133. 
N N Efimov e t  a 1  1983 Proc. 13th  ICRC (Bangalore) - 2 ,  149. 
C T H i l l  and D M Schramm 1985 Phys Rev D 31, 564. 
-
J Lins ley 1975 Phys Rev L e t t  34, 1530. 
J Lloyd-Evans and A A Watson 1982 i n  8 t h  European Cosmic Ray Symposium, 
E d i t o r s  I u c c i  e t  a l ,  Techno p r i n t ,  Bologna p81. 
J Wdowczyk and A W Wolfendale 1984 J Phys G 10,  1453. 
-
71 - cosmic rays  (E > 10'' ev) a r e  u wremarkably i s o t r o p i c .  I n  1 2 1 0  p a r t i c u l a r  we remind t h e  reader  - t h a t  above 3.2 x1019 eV (50 a E 
even t s )  t h e r e  i s  no evidence Q: 
f o r  a g a l a c t i c  p lane  aniso- 
t ropy  bu t  t h e r e  i s  some 
evidence f o r  an  anisot ropy of 
(40 t 20) % i n  a d i r e c t i o n  
n e a r l y  normal (a = 180°) t o  
t h e  g a l a c t i c  p lane .  Of t h e  1 -; 
Figure 3 
8 events  above 10" eV which t * I 
we have observed,  4 a r e  more 
than  40° above t h e  g a l a c t i c  
1J8 1d9 
eV 
10 *O 
plane.  
  s 
 
257 OG 5.3-7 
   
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Arrival direction distribution of cosmic rays of energy 10 (18) eV

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