Considerable interest has developed in the search for local sources of superhigh-energy gamma-rays. The experimental data obtained with the extensive air showers (EAS) array of the Moscow State University are analyzed with a view to searching for the superhigh-energy gamma-rays from various objects and regions of the Galaxy

Fomin, Y. A.

Khristiansen, G. B.

Kulikov, G. V.

Nazarov, V. L.

Silaev, A. A.

Solovyeva, V. I.

Trubitsyn, A. V.

English

NASA Technical Reports Server

259 OG 2°6-I_
SEARCH FOR TF/_ GAM_L_-RAY FLUXES WITH E_ERGIES
ABOVE I0I5 eV FROM VARIOUS OBJECTS
Yu.A. Fomin, G.B. Khristiansen, G.V. Kulikov, V.L. Nazarov,
A.A. 8ilaev, V.I. Solovyeva, A.V. Trubitsyn
Institute of Nuclear Physics, Moscow State University,
119899 Moscow, USSR
ABSTRACT
The experimental data obtained with the EAS array of
the Moscow State University are analyzed with a view
to searching for the superhigh-energy gamma-rays from
various objects and regions of the Galaxy.
Introduction
In recent years, in connection with the activities of the
Kiel group /I/, considerable interest has developed in the
search for local sources of superhigh-energy y-rays. An ex-
cess of the 2xIOI5ev _ -rays from the CygX-3 source was
found in /I/. The Haverah Park group /2/ has confirmed the
results of the Kiel group. The pulsar in the Crab nebula is
another object attracting the researchers' attention. The
Lodz group have detected an excessive Y-ray flux from the
pulsar /3/. However, the Akeno array observations failed to
corroborate this result /4/.
Experiment
We have made an attempt to detect an excessive y-ray flux
from the direction to CygX-3 ( o_o= 307°.8 , _= 400.9). The
EAS array of the Moscow State University is located at an
altitude of I92 m above sea level at a 55°.7 latitude and
has been designed for detecting the showers initiated by the
primaries with energies above IOI5. The shower axis orienta-
tion (the zenith angle _ and the azimuthal angle _ ) was de-
termined using a system of seven scintillators one of which
(of i m2 area) was located at the array center and the re-
maining six (of a 0.5 m2 area each) are located at distances
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2  OG 2.6-14 
SEARCH FO  THE GAMl!JIA-RAY FLU   EN I  
 IOI5 eV FROM I  O E  
Yu.A. Fo in, G.B. hristiansen, G.V. Kulikov, V.L. Nazarov, 
A.A. Silaev, .I. Solovyeva, A.V. Trubitsyn 
Institute of uclear Physics, oscow State niversity, 
II98  os ,  
 
The experi ental data obtained ith the EAB array of 
the oscow State niversity are analyzed ith a vie  
to searching for the superhigh-energy gamma-rays from 
various objects and regions of the alaxy. 
t cti n 
 t ars,  necti n it   ti iti s   
iel group /1/, considerable i terest has developed i  the 
search for local sources of superhigh-energy I-rays. n ex-
cess of the 2xI I5eV I -rays fro  the yg -3 source as 
found i  /1/. he averah ark group / / has confir ed t e 
r sults f t e iel r p. he ulsar i  t e rab e ula is 
other bject ttr ti  t  r s archers' tt ti . e 
Lodz group have detected an excessive I-ray flux fro  the 
ulsar / /. owever, t  keno rr  bservations il  t  
rr borate i  sult / /. 
x.;periment 
We have made an attempt to detect an excessive I-ray flux 
fro  the direction to CygX-3 ( ~o= 307°.8 , s:= 400 .9). The 
S array of t e osco  tate niversity i  l cated at an 
altitude of 192  above sea level at a 55°.7 latitude and 
has been designed for detecting the showers initiated by the 
pri aries ith energies above 1015• The sho er axis orienta-
tion (the zenith angle e and the azimuthal angle ~ ) was de-
ter ined using a syste  of seven scintillators one of which 
(of I m2 area) was located at the array center and the re-
maining six (of a 0.5 m2 area each) are located at distances 
https://ntrs.nasa.gov/search.jsp?R=19850025662 2020-03-20T17:52:57+00:00Z
0G 2.6-14
260
of 60 m from the array center and form a regular hexagen.
The accuracy in determining the angles was 3° for _ and 6°
for _. The shower arrival time was recorded to within Imin.
The observations were carried out from _ay to July,
1982. The total observation time was 890 hours. Of all the
showers detected, IIO00 showers with sizes Ne >_IO5 and S_(_O°
were selected, which made it possible to observe the
declination region _>16 °.
To search for the Y-showers from CygX-3, the showers
were selected whose declinationa were within the interval
_o+ 5°. This declination band was divided into 10° inter-
vals of c_throughout the range of right ascensions start-
ing from the bin do+ 5°. With such a division, the coordi-
nates of the source prove to appear at the center of one of
the bins. After that, we calculated the number of showers
and the observation times for each o_ the bins. Since there
times are different for different bins, we compared bet-
ween the fluxes, i.e. between the ratios of the number of
showers to the time of their observation.
Results
Fig. I shows the dependence of the fluxes on c_in the exami-
ned declination band. The dashed line indicates the value
of the mean flux. It is seen that no excessive flux from
the source was detected.
Fig. 2 shows tae phase distribution of showers for the
IO°xlO ° bin at the center of which the Cy_ X-3 source is
located. The moment to = 2_J+O,9_9.9176 JD was taken to be
the beginning of the period (the zero phase); the period
p = 0.19968I@ day (_ = O) according to the X-ray measure-
m
merit data /5/- The dashed line indicate the number of the
showers calculated on the basis of the mean llux. From the
figure it is seen that there does not exist a singled-out
phase where the Cyg X-3 emission maximum would be observed.
Although we have not found any excessive y-flux f_om
Cyg X-3, we estimated the upper limit of the lOlSe_ Y-rays
f_om the source to be I <3xlO -13 cm-2s "I, which not contra-
OG 2.6-14 
280 
of 60 m from the. array center and form a regular llexagen. 
Tlle accuracy in determining tlle angles was 3° for B and 60 
for lp. The shower arrival time was recorded to within Imin. 
The observations were carried out from May to July, 
, 
1982. The total observation time was 890 hours. Of all the 
showers detected, 11000 showers with sizes Ne ~ 10.5 and 8~"cf 
were selected, which made it possible to observe the 
declination region 0> 160 • 
To search for the l-showers from OygX-3, the sllowers 
w re selected whose declinations w re within the interval 
oo± 50. This declination band was divided into 100 inter-
vals of ~ throughout the range of right ascensions start-
ing from the bin ex'o±.5°. With such a diVision, the coordi-
nates of the source prove to appear at the center of one of 
the bins. After that, we calculated the number of showers 
and the observation times for each of the bins. Since there 
times are different for different bins, we compared bet-
ween the fluxes, i.e. between the ratios of the number of 
showers to the time of their observation. 
Results 
Fig. I shows the dependence of the fluxes on ~ in the exami-
ned declination band. The dashed line indicates the value 
of the mean flux. It is seen that no excessive flux from 
the source was detected. 
Fig. 2 shows the phase distribution of showers for the 
IOoxrOo bin at the center of which tlle Oy~ X-3 source is 
located. The moment to = 2440,949.9176 JD was taken to be 
the beginning of the period (the zero phase); the period 
p = 0.1996814 day (p = 0) according to the X~ray measure-
ment data /5/. The dashed line indicate the number of the 
sllowers calculated on the ba is of the mean flux. From the 
figure it is seen that there does not exist a singled-out 
phase where the Cyg X-3 emission maximum would be observed. 
Although we have not found any excessive l-flux from 
Cyg X-3, we estimated the upper limit of the IOI'eV Y-rays 
from the source to be I < 3xIO-I3 cm-2s -I, which not contra-
• 
2 6 1 OG 2_,6-I_
dict the results of /I/.
It is of interest to compare between the cosmic ray
fluxes from the regions located near the galactic plane
and in high galactic latitudes. Fig. 3 shows the result ob-
tained for all showers on the assumption that the value of
the £1ux is independent of galactic longitude in the obser-
ved interval e = AS°-2IO °, Since it should be expected that
the y-ray-produced showers are "older", we plotted the same
dependenoe for the showers with 3_>I.$ (Fig. _).
As seen from FAgs. 3 and 4, oUr tentative data does
not seen to contradict the assumption of cosmic ray isotro-
py. Further analysis of the experimental data is, however,
necessary. It Should be noted that the same conclusion was
arrived at in /6/, true, at a poorer statistical strength.
References
I. Samorski M., StatureW. Ap.J., I983, v.268, LI7.
2. Lloyd-Evans J. et el. Nature, I983, v.305, P.73_.
3. Dzikows_i T. etal. Proc. ITth ICRG, Paris, I98I, v.l,
p.8.
$. Hare T. et el. Proc. I7th ICRC, Paris, I98I, v.9, P.I79.
5. Parsignault D. et al. Ap.J., I976, v.209, L73.
6. Abdullah _. et el. Proc. ISth ICRC, Bangalore, I983,
v.9, p.2IS.
.... . 
281 OG 2 .... 6-I4 
dict the results of II/. 
It is of intere t to com re betw  the cosmic ray 
fluxes from the region  locate  ne  the g  plane 
and in high g l tic latitude . Fig. 3 shows the res lt ob-
tai~ed for all showers on the assum tio  that the value of 
the flux is indepen t of gala tic longitud  in the ob
ved interval e = 45°-2IOo• Since it should be expected that 
the )'-ray-prod  showers are "old r , we plotte  the same 
dependence for the showers with'S ~ I.4 (Fig. 4). 
As seen from Figs. 3 and 4, our tentative data does 
not seen to co tr i t the assum tio  of cosmic ray isotro-
py. F  analy is of the experim t  data is, ho , 
nec . It shou d be noted that the same con u io  W s 
arri ved at in 161, true, at a poo'rer statistic l strengt . 
References 
I. Sa r i M., stamm W. A . ., I983, v.26 , LI7. 
2. Lioyd-E s J. et ale N t r , 1983, v.3 ,p.734. 
3. Dziko ski T. et ale Froc. 17th IORO, P ris, 1 1, v.I, 
p.8. 
4. Hara T. et ale Froc. 17th lORO, Faris, 1981, v.9, p.I79. 
5. P ig lt D. et ale A . ., 19?6, v.209, L?3. 
6. A lla  M. et ale Pro . 18th IORO, B l , 1983, 
v.9, p.215 • 
262
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Search for the gamma-ray fluxes with energies above 10915) eV from various objects

Search for the gamma-ray fluxes with energies above 10915) eV from various objects

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