The experimental data of extensive air showers observed at Akeno have been analyzed to detect the gamma ray signal from Cyg X-3. After muon poor air showers are selected, the correlation of data acquisition time with 4.8 hours X-ray period is studied, giving the data concentration near the phase 0.6, the time of X-ray maximum. The probability that uniform backgrounds create the distribution is 0.2%. The time averaged integral gamma ray flux is estimated as (1.1 + or - 0.4)x 10 to the -14th power cm(-2) sec(-1) for Eo  10 to the 15th power eV and (8.8 + or - 5.0)x 10 to the 14th power cm(-2) sec(-1) for Eo  6 x 10 to the 14th power eV

Hara, T.

Hatano, Y.

Hayashida, N.

Honda, M.

Kamata, K.

Kifune, T.

Matsubara, Y.

Mori, M.

Nagano, M.

Nishijima, K.

English

NASA Technical Reports Server

67 OG 2.1-5
Gamma Rays of Energy _ I015eV from Cyg X-3
T.Kifune, K.Nishijima*, T.Hara, Y.Hatano, N.Hayashida, M.Honda, K.Kamata,
Y.Matsubara**, M.Mori**, M.Nagano, G.Tanahashi and M.Teshima**
Institute for Cosmic Ray Research, University of Tokyo, Tanashi, Tokyo,
188 Japan
* The Graduate School of Science and Technology, Kobe University, Kobe,
657 Japan
** Department of Physics, Kyoto University, Kyoto, 606 Japan
ABSTRACT
The experimental data of extensive air showers observed at Akeno
have been analyzed to detect the gamma ray signal from Cyg X-3. After
muon-poor air showers are selected, the correlation of data acquisition
time with 4.8 hours X-ray period is studied, giving the data
concentration near the phase 0.6, the time of X-ray maximum. The
probability that uniform backgrounds create the observed distribution is
0.2%. The ti_2av_rage_ integral _mma ray flux is estimated as
(1.1±0.4_10-'_cm-_sec -I for Eo>10'_eV and (8.8_5.0)X10-14cm-2sec -I for
Eo>6XI0"_eV.
I. Introduction
In the energy region larger than I015eV (PeV), Samorski and Stamm
presented in 1983a and b the first evidence from Cyg X-3. The result is
then supported by Lloyd-Evans et al. 1983. They have shown that the PeV
signals are concentrated around the phase of 0.3 where the phase zero
corresponds to the minimum intensity of 4.8 hours variation of X-ray. The
present paper reports another evidence on the positive detection of PeV
gamma rays from Cyg X-3. The data are from EAS observation at EAS Array
at Akeno during 1981 and 1984.
2. Experimental arrangement
EAS Array_at Akeno(Hara et al. 1979) consists of 201 scintillation
counter_ of Im2 area and nine muon(threshold energy is I GeV) detectors
of 25 m_ each. The data recorded by the trigger for small size EAS are
used for the analysis. The region within the circle of 30 m radius near
the center of the array is taken as the detection area of the EAS cores.
This local trigger(called common trigger hereafter in this paper) for
small EAS, of which threshold is about I PeV, is available since 1981
with stable operation conditions and with almost full utilization of nine
muon detectors. The data observed from the beginning of 1981 to September
1984 are dealt with in the present paper. Twenty nine fast timing
detectors are equipped with near the central part of the array for most
of the observation period, giving about 3 degree of resolution in the
arrival direction(Ishikawa et al. 1981). In order to get the events for
the lower gamma ray energy, a temporal high rate trigger(called temporal
trigger) was executed in 1984 only when Cyg X-3 is near the meridian
passage. The threshold energy is about I PeV.
67 G 2.1-5 
a a a s f er  ~ 1015eV from  -3 
. ifune, . ishijima', . ara, . atano, . ayashida, . onda, . a ata, 
. atsub ra", . ori", . agano, . anahashi  . s i " 
Institute for Cos ic Ray Research, niversity of Tokyo, Tanashi, Tokyo, 
8 Ja  
, The raduate School of Science and Technology, Kobe niversity, obe, 
  
" epart ent of Physics, yoto niversity, yoto, 606 Japan 
 
 eri ental   t si e  h er     
have been analyzed to detect the ga a ray signal from yg -3. fter 
uon-p or ir s ers r  s l t , the rr l ti  f t  uisiti  
time ith 4.8 hours -ray period is studied, giving the data 
oonoentration near the phase 0.6, the time of -ray aximu . he 
bability t i  r nds t    i t   
0.2%. The ti~~-av~rage1 integral ~mma ray flux is estifffted as (1.1±O.4~~10- c - sec- f r o)10 e  and (8.8±5.0) 10- cm- 2sec- 1 f r 
1  e e 
1  cti n 
I  t  e er  r i  l r er t a  10 15e  ( e ), a orski a  tam  
r nted i     t  t i ce from  - .  lt  
t e  s ported  l d- vans t ale . e  a e s o  t t t  e  
signals are concentrated around the phase of 0.3 here the phase zero 
corresponds to the minimum intensity of 4.8 hours variation of X-ray. The 
r sent er r rts t er i nce  t  ositi e t ti  f e  
gamma rays fro  Cyg X-3. The data are fro  EAS observation at EAS Array 
t keno uri g   . 
 xperi ental ent 
 rr  at keno( ara t le  nsists f  i till ti n 
counter~ of 1m2 area and nine muon(threshold energy is 1 GeV) detectors 
f   . he at  r r ed  t  tri er f r all i   r  
used f r t e analysis. he region ithin t e ir l  f 30  ra i s near 
t  enter f t  rr  i  t   t  etecti n r  f t   r s. 
This local trigger(called common trigger hereafter in this paper) for 
s all E S, of hich threshold is about 1 Pe , is available sinoe 1981 
it  t le perati n nditi ns  it  l ost l til ti n f i e 
uon detectors. The data observed fro  the beginning of 1981 to Septe ber 
1984 are dealt with in the present paper. Twenty nine fast ti ing 
detectors are equipped ith near the central part of the array for ost 
f t e observation period, giving about 3 degree f resolution i  the 
arrival direction(Ishika a et ale 1981). In order to get the events for 
the lo er ga a ray energy, a te poral high rate tri er(called te poral 
tri er) as e ecuted i  1984 nly hen yg -3 i  ear t e eridian 
passage. he t reshold er y i  out 1 e . 
https://ntrs.nasa.gov/search.jsp?R=19850025609 2020-03-20T17:54:34+00:00Z
68
0G2.1-5
3. Analysis of observed data
Selected as candidates for C_g X-3 signals are the events from the
field of view defined by _I0°X±I0 v square area of the sky around right
ascension 307.6° and declination 40.7°. The data observed exactly within
one period 4.8 hours of X-ray variation per day are used for the analysis
to exclude interference effects between the period and the observation
time.
For each selected event, the ratio, R = N_/Ne, is used to select the
data in favour of gamma rays against normal showers originated by nuclear
active particles. The mean of the total(normal) showers is about R=0.03
and the cut of thedata is set at R=0.001.
Eighteen events have remained after the selection criteria described
above for the common trigger. These events are then checked if they are
correlated with the 4.8 hours periodical variation. The non-uniformity of
the data against the phase of 4.8 hours period is tested by the so called
Rayleigh test, as is also used by Dowthwaite et al. 1982. In the test,
each event is represented by a unit vector in a 2-dimensional space where
the azimuthal angle corresponds to the phase. The norm of the summed
vector over all the events gives the measure of non-uniformity. The
amplitude, a, of the non-uniformity, the norm divided by the number of
events N, is then compared with the expected value from the random walk.
The statistical reliability of the apparent non-uniformity is expressed
by the parameter k=Na /4, where the probability of uniform distribution
producing the observed one is given by exp(-k)(see for example Linsley
1975).
4. Results and Discussions
The number of observed events .... j ....
is plotted in figure la as a [] I EVENT
function of the phase of 4.8 hours
variation, when the period is put hO (b)0.1996854 day as the one by van der
Klis and Bonnet-Bidaud 1981. The [-7
phase zero is defined as the time of II
the minimum intensity of X-ray. The CD '_ [--] _
distribution shown in figure la
gives the value k = 6.2. The
probability that a uniform _O (G)
distribution produces the observed
one is 0.2%. The analyses are done
with various values of test period p O [_ _ _
to see if the non-uniformity occurs 0 0.5
synchronized exactly with the X-ray
period. The result is shown in PHASE
figure 2. The tested periods cover a
wide range of 0.1995 to 0.1999 day figure I. The number of events
and the highest value of k is plotted against phase of 4.8 hrs
obtained at the periods X-ray data variation. (a) common trigger
predict. The periods given by (b) temporal trigger
 
O  2.1-5 
. nalysis  r  t  
Selected as candidates for Clg X-3 signals are the events from the 
fi l  f ie  efi e   ±1 0 1  s are r  f th  s  arou  rig t 
ascension 307.60 and ecli ati n 40.70• he ata observed e actl  it i  
one period 4.8 hours of X-ray variation per day are used for the analysis 
t  l e i t e t  t  t  i   t  servati n 
im  
For each selected event, the ratio, R = N~/Ne, is used to select the 
data in favour of gamma rays against nor al showers originated by nuclear 
t  arti l s.  ea   tb  (n al) ers  ut 0.  
  t f  data  t t O.OO 1. 
i t  nts e ai  r  ti   r  
above f r the co on trig er. hese e e ts are then checked if they are 
correlated ith the 4.8 hours periodical variation. The non-unifor ity of 
t e ata a ai st t e phase f 4.8 hours period is teste  by t e so ll  
ayleigh test, as is also used by owthwaite et al. 1982. In the test, 
eac  ent i  r r s t   a it ct r i  a - i ensional s ace here 
t  i uthal gle rr ds t  t  s .  r  f t  sum e  
vector over ll the events gives the easure of non-unifor ity. he 
plit de, , f t  -unif r ity, t  r  i i   t  ber f 
ents ,  t  pared it  t  ect  al e from t  r nd  al . 
The statistical reliafility of the apparent non-uniformity is expressed 
 t  r eter a 1 , here t  r bability f if r  i tri ti n 
producing the observed one is given by exp(-k)(see f r exa ple insley 
5). 
 esults  iscussi ns 
 ber f ser ed ents 
is plotted in figure 1a as a 
cti  f  hase f .  ours 
variation, when the period is put 
.    t     r 
lis  o net-Bidaud .  
ase r   fi    i  f 
t  i i  i t nsity f -ra . he 
i t ti n n  i r  1  
i ves  al ue   . . h  
probability that a unifor  
istri ti n produces t e bserved 
ne i  .2 . he nalyses r  one 
with various values of test period p 
to see if the non-uniformity occurs 
nchronized actly it  t  -r  
eri . he sult  n  
fi re . he t t  eri ds ver  
ide r ge f .  t  0.  a  
 t  ighest alue f  i  
btai ed t t  eri ds -ray ata 
redict. he eri ds i en  
o 1 T 
.  
HASE 
( ) 
(0) 
1 
figure 1. The number of events 
plotted against phase of 4.8 hrs 
variation. (a) common trigger 
(b) temporal trigger 
@@
Og 2.1-5
Parsignault et , ,
al. 1981 and tO _. '-
van der Ells . •
andBonnet- ABidaud 1981 are . .
shown by arrows -.T • • : •
in the figure. : • : •
Another high -_ • _ : "
value of k C_ J _" •
appears around : . /
p = 0.19975. : " •
ThiSoanbeside peak ,_%_. /_._.J , L_/. _%../
understoodas 1995 .1997 .1999
the second best PERIOD(DAY)fit which is
created by a
combined effect figure 2. The parameter k of statistical significance
of the of non-uniformity is plotted against the test period
synchronization
at the X-ray period and the data of the largest interval of acquisition
time.
The off-source data selected by the same criteria for on-source both
in the field of view and in Np/Ne cut are also analyzed to get the
spurious correlation with the X-ray period. The parameter k of non-
uniformity are plotted in figure 3a as a function of right ascension,
where the off-source directions are defined. Declination is set between
30.7e and 50.7°. The off-source data sets give no larger non-uniformlty
than the on-source data set. In figure 3b, the integral spectrum of k is
plotted. The k-spectrum is well explained by the statistical fluctuation,
which is given by the function exp(-k) (straight llne in the figure
normalized by the total number of the data sets for different directions
" in the sky), except the largest value 6.2 for the on-source data set.
The number of data in the temporal trigger is too small to get a
statistically meaningful arguments. The distribution versus phase is,
. however, consistent as is shown in figure Ib with the result by the
common trigger.
Our data confirm the conventional view that the gamma ray EAS has a
poor containment of muon, on the oontrarFto the result by 3amorskl and
Stamm 1983e. While, the data out by shower age afber Kiel group produces
no significant result(k=0.6). This may suggest that our trigger for data
recording is biased in small Ne region, inefficient to flat EAS's of old
shower age initiated by gamma rays.
The other kind of systematic errors arises from the ambiguity in
data cut by N_/Ne. The result for the loose out in Np/Ne smaller than
0.003 and 0.01 results in the concentration of events at the phase near
0.6 is observed with less significance of k=2.4 and 1.6, respectively.
The number of counts around@ =0.6 exceeds the average by 16 and 28,
respectively. If these excess is attributed to the signal, the obtained
flux could be at most doubled. In figure la, the extraction of seven
events at phase 0.6 results in k=1.0, which may indicate that about 7
events could be attributed to the signal.
Parsign l t et 
ale 1981 and 
van der Klis 
and Bonnet-
Bidaud 1981 are 
shown by arrows 
in the figure. 
A ther high 
value of k 
appears around 
p = 0.19 75. 
This side peak 
oan be 
understood as 
the seoond best 
fit which is 
cr ted by a 
oombined effeot 
of the 
sync r i ti  
N 
'of\. , 
·0 
. 995 
•• 
. 
. 
• 
. 
.. 
•• 
. . 
'11'. .  
. . 
I 
. " 
. ' V' 
,A 
. . 
, . 
. . 
. 
. 
, 
, 
. 
.1997 
PERIOD (DAY) 
OG 2.1-5 
. 
/:. 
. 
.199  
figure 2. The param  k of statistioa  significano  
of non-u for i  is plotted against the test period 
at the X ray period and the data of the largest interv  of acq tion 
time. 
The off-souroe data seleoted by the same criteria for on-souroe both 
in the field of view and in N~/Ne cut are also analyzed to get the 
spurious correlation with the X-ray period. The param ter k of non-
uniform y are plotted in figure 3a as a funotion of right ascension, 
where the off-souroe directions are defined. Deolination is set between 
30.70 and 50.70 • The of -souroe data sets give no larger non-u for i  
than the on-source data set. In figure 3b, the integra  speotrum of k is 
plotted. Th 'k-spectrum is w l  explaine  by'the statistic  fluctuation  
w ich is given by the funotion exp(-k) (straight line in the figure 
norm l  by the total num r of the data sets for dif eren  direotions 
in the sky), except the large  value 6.2 for the on-souroe data set. 
The num r of data in the tem r l trig er is to  sm ll to get a 
statistic  m i  argum . The distribution versus phase is, 
how  oo sten  as is shown in figure 1b w th the res  by the 
com  trig er. 
O r data confirm the oon ti l view that the gam a ray EAS has a 
poor containm t of m n, on the c ntrary t  the resu t by Sam i and 
Stam  1983c. Whil  the data cut by show r age af'cer K  group produoes 
no significa t result(k=0.6). This may sugg t th t our trig er for dat  
recording is biased in sm ll Ne region, inefficient to flat EA 's of old 
show r age initiated by gam a rays. 
The other kind of system tic er ors arises from the am i ity in 
data out by N~Ne. The resu t for the lo se out in N~/Ne sm l  than 
0.0 3 and 0.01 results in the oo tr tio  of events at the phase near 
0.6 is observ  w th less signifioano  of k=2.4 and 1.6, respeo ! . 
The num  of coun s around 4> =0.6 exceeds the averag  by 16 and 28, 
resp . If these excess is at ributed to the sign , the obtained 
flux could be at m t doubled. In figure 1a, the extraotion of seven 
eve t  at phase 0.6 res lts in k=1.0, whioh may indicate that about 7 
eve ts could be attributed to the sign l. 
7O
0G2,1-5
T_e integral flux is49_ta_ned _s (1.1±0.4)X10_,14cm-2seo-I for
Eo>lO'_eV and (8.8±3.8)X10-'_om-_seo'' for Eo>6XIOI_ev, by taking 7 and 3
events near 0.6 phase in figure la and b as the signals and by correcting
for the inefficlenoy due to the trigger bias. The given errors are the
statistical errors and the systematic errors can allow larger fluxes than
the quoted ones.
The preoedlng results of Klel and Haverah Park have a sharp peak at
the phase 0.3, while the present result shows a broader one near the ,_
phase of 0.6 at the X-ray maximum intensity rather colnoident with 10'CeV
results.
U_/
0
04 o
O0 0 0
0 LL.I
0o%_ ° Co o ._0%°, o _,° _o,
o 0 180 360° z , ,
RIGHT ASCENSION 2 4 6 k
figure 3. (a) The parameter k is plotted for the data sets from
various direction of the sky. (b) Integral spectrum
Acknowledgements
The authors are indebted to the technical staffs in Akeno Crew for
obtaining and analyzing the data. The data reductions are done by FACOM
M380 at the Computer Room, Institute for Nuclear Study, University of
Tokyo.
J
References
Dowthwaite, J.C. et al. 1982, Prec. Int. Workshop on High Energy Gamma
Ray Astronomy at Ootacamund, India, 97.
Elsner, R.F. et al. 1980, Ap. J., 239, 335.
Hara, T. et al. 1979, Proc. 16th ICRC(Kyoto), _, 135.
Ishikawa, F. et al. 1981, Proc. 17th ICRC(Paris), _, 141.
Linsley, J. 1975, Phys. Rev. Lett., 34, 153.
Lloyd-Evans, J. et al. 1983, Nature, 2u0_ 784.
Parsignault, D.R. et al. 1976, Ap. J.(Letters), 209, L73.
Samorski, M. and Stamm, W. 1983a, Ap. J.(Letters), 268, L17
Samorski, M. and Stamm, W. 1983b, Proo. 18th ICRC(Bangalore), i, 135.
Samorski, M. and Stamm, W. 1983c, Proc. 18th ICRC(Bangalore), 11, 244.
Van der Klis, M. and Bonnet-Bidaud, J.M. 1981, Astron. Ap.(Letters), 95,
L5.
70 
OG 2.1-5 
The integral flux is Qbtained as (1.1± 0.4)X10-14 -2sec-1 for Eo>10 5eV and ( .8±3.8)X10-1~cm-2sec-l for Eo>6X1014ev, by taking 7 and 3 
vents near 0.6 phase in figure 1  and b as the signals and by correcting 
for the inefficiency due to the tri ger bias. The given er ors are the 
s atistical er ors and the ystematic er ors can allow larger fluxes than 
the quoted ones. 
The pr ceding results of Kiel and Haverah Park have a sharp peak at 
the phase 0.3, while the pr sent result shows a broader one near the 
phase of 0.6 a  the X-ray maximum intensity rather coincident with 1012eV 
results. 
I 
• 
~ 0 
~ 
0 
N 0 a:: 00 0 
0 W 
0 00 
0 roo ~ <hOooQoo~ 0 ",0 2:~ 0 0 n 0 180 3600 ::J z 
RIGHT ASCENSI  2 4 6 
figure 3. (a) The p rameter k is plotted for the d ta sets from 
various direction of the sky. (b) Integral spectrum 
Acknowledgements 
The authors are indebted to the technical staffs in Akeno Crew for 
obta ing and nalyzing the d ta. The d ta reductions are done by FACOM 
M380 at the Computer Room, Ins i ute for Nuclear Study, University of 
Tokyo. 
References 
Dowthwaite, J.C. et ale 1982, Proc. Int. Workshop on High Energy Gamma 
Ray Astronomy at Oot camund, India, 97. 
Elsner, R F. et al. 1980, Ap. J., n.9., 335. 
Hara, T. et al. 1 79, Proc. 16th ICRC(Kyoto),,a, 135. 
Ishik wa, F. et al. 1981, Proc. 17th I RC(Paris),,a, 41. 
Linsley, J. 1975, Phys. Rev. Lett., .3.!., 153. 
Lloyd-Evans, J. et al. 1983, Nature, ..3.Q5., 784. 
Parsignault, D R. et ale 1976, Ap. J.(Letters), ~  L73. 
Samorski, M. and Sta m, W. 1983a, Ap. J.(Letters), ~  L17 
k 
Samorski, M. and Sta m, W. 1983b, Proc. 18th ICRC(B ngalore), ~, 135. 
Samorski, M. and Sta m, W. 1983c, Proc. 18th ICRC(B ngalore), 1, 244. 
Van der Klis, M. and Bonnet-Bi aud, J.M. 1981, Astron. Ap.(L tters), .2.5., 
L5. 


Gamma rays of energy  or = 10(15) eV from Cyg X-3

Gamma rays of energy or = 10(15) eV from Cyg X-3

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