A search for super-high energy gamma-ray point sources has been carried out. The well known source Cyg X-3 was observed first and preliminary results of data analysis are presented. There is not positive excess of showers from the source region, but phase analysis discovers a small pulse at phase 0.6 which corresponds to the integral flux (6 + or - 3) X 10 to the minus 14th power cm-2 sec-1 at E sub gamma  3x10 to the 14th power eV

Alexeenko, V. V.

Chudakov, A. E.

Khaerdinov, N. S.

Lidvansky, A. S.

Navarra, G.

Ozrokov, S. S.

Sklyarov, V. V.

Tizengauzen, V. A.

English

NASA Technical Reports Server

9 1 OG 2.1-12
A SEARCH FOR GAMMA-RAY POINT SOURCES WITH "THE CARPET"
SHOWER ARRAY
V.V.Alexeenko,A.E.Chudakov,N.S.Khaerdinov,A.S.Lidvansky,
G.Navarra#,S.S.Ozrokov,V.V.Sklyarov,V.A.Tizengauzen
Institute for Nuclear Research of USSR Academy of Sciences,
Moscow,USSR
# Institute of General Physics of University of Turin,ltaly
An experiment aiming at search for super-high energy
gamma-ray point sources has been put into operation at
Baksan Valley,Northern Caucasus.The well known source
Cyg X-3 was observed first and preliminary results of
data analysis are presented.There is no positive excess
of showers from the source region,but phase analysis
discovers a small pulse at phase 0.6 which corresponds
to the integral flux (6±3).10 -14cm-2sec-1 at E_>3-1014eV.
The X-ray source Cygnus X-3 was observed with Cerenkov
light technique in TeV energy range (for a brief review see
/1/_Recently results obtained with classical EAS method/2,3,
4/ have pointed out that spectrum of Cyg X-3 gamma-rays,pro-
bably,extends up to 1015 eV.In this paper we try to confirm
this result observing the source in energy range where up
to now there were no data.
Baksan air shower array consists of "the Carpet" in the
centre and 6 outside detectors at distances 30 and 40m(fig.
1).Four hundred 0.5 m 2 scintillators of the Carpet are divi-
ded in four groups (_-_) feeding the four-fold coincidence
circuit with output counting rate 50 per sec.This signal
is used as starting pulse for time measurement of delays of
outside detectors.Time measurement system has a compensation
of pulse hight dependence of delays.The step of delay measu-
rements is 1 nsec.
Each outside detector consists of 18 scintillators (total
area 9 m2).Four of them (1,2,5,6 in fig.l) in coincidence
with four-fold signal of the Carpet give trigger pulse for
the recording. The energy thresholds are: 0.3 of the pulse
hight o_[fa penetrating particle for each quarter of the Car-
pet i-IV ,and _i penetrating particle for outside detectors
i,2,5,6.The counting rate of the trigger_0.8 per sec.
Fig.2 presents calculated energy spectra of showers for
this trigger and for different indices of power law gamma-
ray spectrum: _=2.71 and _=2.0.Median energies of distribu-
tions of fig.2 are indicated by arrows.They are equal to 75
and 300 TeV.
Angular resolution of shower arrival direction measure-
ments was estimated using the distribution of experimental
value A :(TI-T2)-(T5-T6),where Ti - the delay of detector
number i.Fig.3 presents this distribution for one day of ob-
servation,r.m.s, f it _ corresponds to angular re-
A_~1.2°°v. :5.2 nsecsolution
The Cyg X-3 observations have started in July 1984 and
 OG 2.1-12 
 H  MA-RAY I  CES I   PET" 
ER Y 
. .Alexeenko,A.E.Chudakov,N.S.Khaerdinov,A.S.Lidvansky, 
. avarra#,S.S.Ozr kov,V.V.Sklyarov,V.A.Tize gauzen 
I stitute f r uclear esearch f SS  cade y f ciences, 
oscow, SR 
# I stitute f eneral hysics f niversity f urin,Italy 
n experi ent ai ing at search for super-high energy 
a ma-ray int s rces s ee  t i t  eration t 
aksan alley,Northern aucasus.The ell kno n s rce 
 -  as served t  r li inary sults f 
ata alysis r  r sented.Th re i   ositive cess 
of sho ers fro  the source re i n,but phase a alysis 
i vers  all ulse t ase .  hich rr s onds 
to the integral flux (6±3)·10 -14cm-2sec-1 at Er>3·1014ev. 
 -ray rce ygnus -  as served it  erenkov 
li t t nique i  e  er y r e (f r a rief r i  s  
I1/ARecently results obtained ith classical E S ethod/2,3, 
41 ave inted t t t s ectr  f y  -  a ma-rays,pro-
bably,extends up to 1015 e .In t is paper e tr  to confir  
t i  r sult serving t  s r e i  e er y r e here  
  re ere  t . 
aksan ir s er rr  nsists f "t  arpet" i  t  
centre and 6 outside etectors at ista ces 30 and 40 (fig. 
l). ur ndred .  2 i tillators f t  arpet r  i i-
ded i  four groups . <l-lJL) feeding t e f r-fold coincidence 
ir uit it  t ut unting t   er . his i al 
is used as st rti g lse f r ti e easurement f delays f 
utside etectors. ime easurement t  s  pensation 
f ulse i ht dependence f ela s. he ste  f delay easu-
.. ents   c. 
ach utside etector nsists   i tillators t t l 
r a  2 ). our f th  ( , , ,  i  i .l) i  i cidence 
it  f r-fold si al f t e arpet i e tri er lse f r 
t  r ing.T  r y t olds : .   t  lse 
high~ f a enetrating article f r eac  uarter f t e ar-
et 1-1:1 ,and ...... 1 enetrating article f r outside etectors 
1,2,5,6. The counting rate of the trigger - 0.8 per sec. 
Fig.2 presents calculated energy spectra of sho ers for 
t is tri er and f r ifferent i ices f po er la  ga a-
ray spectru : ¥~2.71 and t~2.0.Median energies of istri u-
ti s f fi .  r  i icated  rr s. hey r  ual t   
  . 
ngular resolution of sho er arrival direction easure-
ents as esti ated si  t e istri ution f e peri ental 
value L1=(Tl-T2)-(T5-T6),where i - the delay of detector 
nu ber i. i .  resents t is istri ution f r one day of ob-
servation,r.m.s. of it 6~5.2 nsec corresponds to angular re-
l ti n .6.8", 1. 2°. 
The Cyg -3 observations have started in July 1984 and 
https://ntrs.nasa.gov/search.jsp?R=19850025615 2020-03-20T17:54:58+00:00Z
92 OG 2.1-12
I i I I
_ 0- 2
g .0
5 }
.Ta
N _ _0-
Fig.i Plan view of Baksan array
H E_(GeV) \
Fig.2 Response functions of the array ' . , , ,
for different energy spectra of_rays 104 105 i06
in this paper we present preliminary results of analysis of
242 days data sample.The source was observed 5 hours per day
(±2.5 h from culmination) and total number of registered sho-
wers exceeds 3.10°.Counting rate from the cell centered on
the source position andhaving the form of a circle with ra-
dius 2.5 ° in equatorial coordinates was compared with the
rate of 4 off-source cells of the same form and size,but
shifted by ±5 ° along _ and ; .After correction of data for
atmospheric pressure and angular distribution of showers,the
signal Ncv _ and mean background Nb(a quarter of total coun-
ting rate-_f four off-source cells) were determined.Both we-
re phase-analysed then using ephemeris from /5/.
The ratio Ncyg/N b is presented versus phase in fig.4.1t
can be easily seen, that there is no absolute excess from
the Cygnus cell,mean value of Nc_/N b is equal to 0.992±.008.
Nevertheless,there is slight positive excess (3.6 _ in 12th
bin) in phase curve (fig.4) near the phase 0.6.
The value of gamma-ray flux and typical energy of recor-
ded showers both depend in our case on the proposed spectral
index of the source.As extreme values we used _=2.71,typical
for cosmic rays near the Earth,and _=2.0,which seems to be
in approximate accordance with different experimental data
(see,for example,/4/).For both of them we present in fig.5
upper limits of gamma-ray flux derived at 95% confidence le-
vel from the fact of absence of absolute excess without pha-
se analysis.
Also shown in fig.5 is the point estimated from phase 0.6
excess using [=2.0 only (median e_ergy 300 TeV).The obtain-
ed flux is I_(> E) = ( 6 ± 3).10 -14 cm-2sec-l.This point
seems to be in disagreement with the results of other expe-
rimental groups,especially that of Kiel group /3/,where the
threshold energy is byan order of magnitude larger,but the
value of flux is of the same order as ours.
82  . - 2 
1 
0 n 
I 
-2 ?  Q) 
('J 
n 
II 1.Y 4 I C) 
CJ Q) UJ 
I III (\J I 
S 
C) 
:>, 
+> 
• .-1 
UJ 
 ~ Q) 
+> 
ig.l vie  s.::: Plan f aksan arra  H E,r(GeV) 
i .2 esponse f cti ns f t e arra  
for different energy spectra of 'I-rays 4 5 1 6 
in t is paper e present preli inary results of analysis of 
242 days data sa p1e.The source was observed 5 hours per day 
( 2.5 h fro  cu1m~nation) and t tal nu ber f re istered sho-
ers ceeds ·  .Counting r t  fro  t  ll ntered  
the source osition and having the for  of a circle ith ra-
i s . 0 i  uatorial c ordinates as co pared ith t e 
rate of 4 off-source cells of the sa e for  and size,but 
ifted  5° l g ~  g . fter rrection f ata f r 
at ospheric pressure and angular istri ution of showers,the 
signal cyg and ean background b(a quarter of total coun-
ti  rate of four off-source cells) ere deter ined.Both e-
r  hase-analysed t  si g hemeris fro  1 /. 
The ratio Ncyg/Nb is presented versus phase in fig.4.It 
ca  e asily s n, t t t re i   solute cess fr  
the Cygnus cel1, ean value of Ncyg/Nb is equal to 0.992±.008. 
evertheless,there is slight pos1five excess (3.6 ~ in 12th 
i ) i  phase curve (fi . ) near the phase . . 
The value of ga ma-ray flux and typical energy of recor-
e  s ers t  depend i  r case on t e r osed s ectral 
index of the source. s extre e values e used r 2.7l,typica1 
f r c s ic r s ar t  arth,and t .0, hich see s t  e 
in approximate accordance ith different experimental data 
(see,for examp1e,/4/).For both of them we present in fig.5 
upper li its of ga ma-ray flux derived at 95% confidence le-
el fr  t  f t f sence f solute cess it out a-
 alysis. 
lso sho n i  fi .  is the point esti ated fro  phase 0.6 
excess u~ing Y=2.0 only ( edian energy 300 e ):The ? tain-
ed flux 1S I~(> E) = ( 6 ± 3)·10-1~ c - 2 sec- l .Th1S p01nt 
see s t  be i  disagree ent ith t e results f t er expe-
ri ental groups,especia11y that of Kie1 group 13/,where the 
threshold energy is by an order of agnitude 1arger,but the 
l e f   f  e r er  urs. 
.. 
g3 OG 2.1-12
__ 4d
  1o3r1 00
I I I
-21 -15 -9 -3 +3 0 .2 .4 .6 .8 1.
A(nsec) X-ray phase
Fig.3 Distribution of Fig.4
difference of differen- The ratio of counting rate in
ces of delays for one Cyg X-3 cell to the mean of 4
day of observation "off-source" cells versus phase
Taking into account the absence of absolute excess we
have to conclude that obtained so far Baksan experimental
data do not give a good confirmation of the very existence
of high energy gamma-ray flux from Cygnus X-3.
We plan to accumulate more data on Cyg X-3 and to look
at other potential sources also.
References
i
J
1. A.A.Stepanian. Adv. Space Res.,3,123(198_) i
2. C.Morello,G.Navarra,S.Vernetto. 18th Int.Conf.on i
Cosm. Rays,Bangalore,_,127(1983)
3. M.Samorsky,W.Stamm. Astroph.Journ.Lett.,268,L17(1983)
4. J.Lloyd-Evans et al. Nature,305,784(1983)
5. M.van der Klis,J.M.Bonnet-Bidaud. Astroph.Journ.Lett.,
95,L5(1981)
b
I
93 OG 2. -12 
rn 3.10 3 
H 1.1 
([) 
:s: 2d 
o 
~ 2.10 3 
~ 
o 
H ([) 0 3 
'@ 
;:5 
:z: 
-2cS 
-21 -15 -9 -  +3 
A(nsec) 
Fig.3 Distribution of 
ifference f ifferen-
ces of delays for one 
o  .  .  .  
-ray ase 
Fig.4 
The rati  of counting rate i  
Cyg -3 cell to the ean of 4 
. 
day of observation "off-source" cells versus phase 
Taking into account the absence of absolute excess we 
have t  conclude t at obtained so far aksan experi ental 
data do not give a good confir ation of the very existence 
of high energy gamma-ray flux from Cygnus X-3. 
We plan to accumulate more data on Cyg X-3 and to look 
at other potential sources also. 
eferences 
1. . .Stepanian. dv.Space Res.,~,123(1984) 
2. C. orello,G.Navarra,S.Vernetto. 18th Int.Conf.on 
Cos .Rays,Bangalore,1,127(1983) 
3. .Samorsky, .Stamm. stroph.Journ.Lett.,268,L17(1983) 
4. J.LloYd-Evans et ale ature,305,784(1983) 
5. .van der lis,J. .Bonnet-Bidaud. stroph.Journ.Lett., 
95,L5(1981) 
94
OG 2.1-12
! ! ! ! t
\
\
10 11
- )\
\
\ /_:2.71 } without
10-12 \ phase analysis
: .0
I
10_13 o
I
0
10_1_ m :2.0 with \A \
_ phase analysisH \
\
\
i0-15 \
V Cerenkov
• } experiments \
_ - \
Plateau Rosa \
-16 \ -
10 _ Kiel ,
Havera Park _ I| _...... ! ,,, t . ! .....
1013 1014 1015 1016 E_(eV)
Fig.5
Integral gamma-ray flux from Cyg X-3
'""" I 
(\J 
I 
C) 
(l) 
[[) 
S 
C) 
94 
Cerenkov 
experiments 
Plateau Rosa 
Kiel 
Havera Park 
Fig,5 
OG 2,1-12 
I 
Integral gamm -ray flux from Cyg X-3 


A search for gamma-ray point sources with the Carpet shower array

A search for gamma-ray point sources with the Carpet shower array

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