The detection of the 0.511 MeV electron positron annihilation line coming from the Galactic Center to provide the means to estimate the rate of positron production and to test some theoretical sources of positrons is addressed. The results of the measurements of the 0.511 MeV line flux made with a gamma ray experiment on board a stratospheric balloon are presented. The detector field of view looked at the galactic longitude range -31 deg  l(II)  +41 deg. The observed flux is 0.0067 (+ or - 0.0005) photons 1/cm(2)5 which is in very good agreement with the expected flux when assuming that the Galactic Center is a line source emitting uniformly

Benson, J. L.

Jardim, J. O. D.

Jardin, M. V. A.

Martin, I. M.

English

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SECRETARIA DE PLANEJAMENTO DA PRESIDENCIA DA REPUeLICA9- CONSELMO NACIONAL DE DESENVOLVIMENTO CIENTIFICO E TECNOL001C0INSTITUTO DE PESQUISAS 	 ESPACIAIS
(NASA —CR-164130)	 8tASUSEME81 OF THE U.511
	 ddl -zzy65
KeV GAMMA P.3Y LIbE FROM THE GALACTIC CEblEd
(IAStituto dC PeSgUiSaS hSjidC1u1S, Sao Jose)
8 p 8C A02/MF A01	 CSL;L U38
	 ULC1dS
G.1/ y ^ 1174
1.Classific400n INPE-COM.4/RPE 2.Period 4.Oistribution
ICriterion
CDU: 523.03
internal3-Key Words (selected by the author)
GANfA-RAY LINES; GALACTIC CENTER;
FLFI'TRoN-POSITRON ANNIHILATION external	 x
a
5.Report No. 6.Oate 7.Revised byes.
INPE-2004-P.PE/286 February, 1981 ^Daniel J.R:JNordemann
8. Title and Sub-title 9.Authori2ed by
MEASUREMENT OF THE 0.511 MeV Y-RAY LINE
FROM THE GALACTIC CENTER Nelson de J^arada
Director
10.Sector	 DAS/DAE	 Code 30.292. ll.No. of Copies	 11
12.Authorship	 J.O.D. Jar-dim
14.No. of Pages -	 09J.L. Benson
M. V.A. jar-dim
I.M. Martin
13.Price
13.Signature of first author
16.Summary/Notes 	 The detection of the 0.511 AfeV electron-positron annihi
lacion line coming from the Galactic Center can provide the means to estima
to the rate of positron production and to test some theoretical sources of
positrons. In this work we present the result of the measurements of the
0.511 MeV line flux made with a gamma-ray experiment on board a stratosphe-
ric balloon. The detector field of view looked at the galactic longitude
range -310<AII<+410. The observed flax is (6.70±0.50)x10-3 photons CM- 28-1,
which is in very good agreement with the expected flux when assuming that
the Galactic Center is a line source emitting uniformly.
17.Remarks	 This work was part ally s ,^pported by the "Fundo NacionaZ de De
senvolvimento Cientifico a Tecnol6gico - FNDCT", under contract FINEP-CT`
5:37. This work will be pub7leheci in the Proceedings of the "II Reunion La-
tino-Ameri.can,a de In Ilnicrt its, Aetron_^.rnla tnternacional"	 Merida,	 Venezuela.
t
MEASUREMENT OF THE 0.511 MeV y-RAY LINE FROM THE GALACTIC CENTER
J.O.D. JARDIM, J.L. BENSON*, M.V.A. JARDIM AND I.M. RAVIN
Instituto de Pesquisas Espaciais - INPE
Conselho Nacional de Desenvolvimento Cientifico a Tecnologico - CNPO
Sao Jose dos Campos, S.P., Brasil
RESUMO
A detecgao do fluxo da linha de aniquilagao eletron-positron em 0.511
MeV proveniente da diregao do Centro Galatico fornece condigoes de esti
mar a taxa de produgao de positrons a de testar algumas fontes de posi
trons teoricas. Neste trabalho apresentamos o resultado de medidas da li
nha 0.511 MeV, obtidas com um experimento para medir raios gams a bordo
de um balao estratosferico. 0 angulo de visada do detetor observou o dis
co galatico no intervalo de longitude -31 0<z Il <+41 0 . 0fluxo observado e
(6.70±0.50)x10-3 fotons cm- 2 s-1 , o qual concorda muito bem com o valor
de fluxo calculado supondo-se que o Centro Galatico a uma fonte linear
emitindo uniformemente.
ABSTRACT
The detection of the 0.511 MeV electron-positron annihilation line
coming from the Galactic Center can provide the means to estimate the
rate of positron production and to test some theoretical sources of
positrons. In this work we present the result of the measurements of
the 0.511 MeV line flux made with a gamma-ray experiment on board a
stratospheric balloon. The detector field of view looked at the galac-
tic longitude range -31 0<i II <+41 0 . The observed flux is (6.70+0.50)x10-3
photons cm-2 s-1 , which is in very good agreement with the expected flux
when assuming that the Galactic Center is a line source emitting uniform-
ly.
'	
Key words: GAMMA-RAY LINES-GALACTIC CENTER-ELECTRON-POSITRON ANNIHILATION.
* Present Address: Max-Planck Institut fur Aeronomie, Lindau, FRG.
t
I. INTRODUCTION
The search for the 0.511 MeV elec-
tron-positron annihilation line flux
emitted from the Galactic Center (GC)
region has been a difficult task to
achieve by the few groups working in
gamma ray spectroscopy since the ob-
servation made by Haymes et al. (1975).
They used a telescope with about 13°
full width at half-maximum (FWHM) an-
gular resolution and reported a flux
coming from -40<1 11 <+60 galactic lon-
gitude interval as (8.0±2.3)x10-4pho-
tons cm 2s	 for the 0.511 MeV line.
Li±ter, Leventhal et al.	 (1978) flew
a telescope from Alice Springs (Austra
lia) with 450 FWHM angular resolution
and using a large high-purity (HP) Ce
detector of 130 cm 3 . They reported a
0.511 MeV line flux of 	 (1.22±0.22)x10'3
photons cm- 2 s -1 coming from the GC.
Due to a Brazilian-French collabo-
rative program, a telescope using a
large Ge(Li) e-ystal of 140 cm 3 has
flown from Guaratingue 6 (Brazil), in
1977, on board a stratospheric balloon
(Albernhe et al.,	 1977) . Da Costa (1980) ,
analyzing the data obtained from two
flights,	 calculated an intensity of
(4.19'1.56)x10- 3photuns cm-2 s- 1 forthe
0.511 MeV line flux from the Galactic
Center.
In this paper we report the measure-
ment of the electron-positron annihila-
tion line emitted from the GC disk in
the -31 0<1 11 < +41 0 longitude interval
using the upper NaI(Tl) detector of a
balloon borne telescope.
The payload was launched from Cacho
eira Paulista	 (22 040'S, 45oW),	 Brazil,
in March 29,
	 1980.
We measured an intensity of	 (6.70±
0.50)x10- 3photons cm-2
 s - I	 for the 0.511
MeV line coming from the GC direction.
II. THE EXPERIMENT AND THE FLIGHT
The telescope is made up of two
10.16cm x 10.16cm cylindrical NaI(T1)
crystals separated vertically by 90cm
and a 20cm diameter cylindrical lead
(Pb) shield, Scm thick, is placed in
f.
between the detectors. Each detector is
surrounded by an aluminum powder shield
and has a 1.5cm thick NE102A plastic
scintillator in front of the crystal
in order to reduce some of the charged
particle background.
The array defines an aperture angle
of 300 FWHM at about 1.2 MeV when we
make the differences in counting rate
between the upper and lower detector
as a function of angle.
Each detector is connected to a RCA
8054 photomultiplier and to a 128 chan-
nels SEZN encoder in order to provide
the spectra in the 0.3 to 3.0 MeV energy
interval.
A complete description of the teles-
cope will be given by Benson et al.
(1981).
The payload was carried aloft by a
stratospheric balloon (74,000m 3 ) which
was launched at 02:07UT in March 29,
1980.
s
	
	
The balloon reached the ceiling of
about 4 millibars at 04:04UT and the
flight duration was 15 hours, as it was
discontinued by a pyromechanical device
for purposes of recovering.
The pressure data was obtained using
a Rosemount pressure sensor.
The encoded signals, pressure and
temperature data as well as azimuthal
i	 directions obtained from two crossed
ftuxgate magnetometers were telemeter-
ed to the ground via FM-FM telemetry.
We observed the transit of the CC
through the field of view of the teles-
cope.
To calculates the flux at the 0.511
MeV line due to the CC we used only the
s	 upper detector assembly (FWHM=72 0) for
which the setting was about 25keV/chan-
r
	nel. If we had used the telescope in
its present electronic configuration
for this purpose it would have been
difficult to locate the peak position
with confidence.
The measured energy resolution is
14% at 0.511 MeV for the 4"x4" NaI(T1)
crystal.
t
pIII. RESULTS AND CONCLUSIONS
In Figure 1 is shown the path of the
balloon in galactic coordinates after
the payload reached the ceiling.
f
CE^M4	 wr j
--- T
f
-o}
FIG. 1. Path of the balloon in galac-
tic coordinates after reaching the ceil-
ing.
We show in Figure 2 the average fluxes
for the background (BKC) and for the re-
gion where the axis of the telescope was
looking toward the galactic coordinates
ZII - 5.54" and b lI - + 1.92 0 , i.e.,
when the region in galactic latitude
ranging from -31 0 up to +41 0 was within
the FW11M of the upper detector.
From the measurements and after tak-
ing into account the atmospheric absorp-
tion (Fig. 2) we calculated theflux com-
ing from the GC direction as being (6.70;
0.50)x10-3 photons cm-2s
If we assume that the galactic disk is
a line source emitting uniformly the 0.511
NeV line radiation we can use the results
estimated from the observations.
On the other hand, the highest esti-
mated value from theoretical models for
s
the intensity of the 0.511 MeV line due
to electron-positron annihilationis gi-
ven by Stecker (1971) as 2x10-3photons
cm 2s-lsr-l.
If we use our result and the detec-
tor solid angle to transform the flux
into	 the same units used by Stecker
(1971) we get 5.58x10-3 pliotons cm-=s-1
sr-1 , which is about 3 times higher than
the theoretical estimate.	 It suggests
that other sources of positrons are need-
ed to explain the observations.
It is worth to note that the GC line
emission profile appears to be more alike
a f lat extended source than to be a point
source with a few degrees wide.
Finally, the fact that Mandrou et al.
(1980) give only an upper limit flux for
that line seems to suggest that the ex-
tent of the 0.511 MeV emitting region is
less than 90oFWHM in longitude.
REFERENCES
Albernhe,	 F.;	 Boclet,	 D.;	 Claisse,	 J.;
Durouchoux, Ph.;	 Frabel,M.; Marques ,
J.;	 Olivier,	 E.; Pagnier, P.; Rocchia,
R.	 and Vedrenne, G.	 1 9 77,	 in	 a•
Frascati,
	
Italy,
24-27 May,
	
1977,	 ESA SP-124,	 1).	 293.
Benson,
	
J.1.. ;	 Jardim,	 J.0.1). ; Martin, I.
M.; Jayanthi,	 U.B.	 and Aguiar, O.D.
1981,	 in preparation.	 (to be present-
ed	 at	 the
	 !'?:	 ..C...'.,	 Paris,	 13-
25 Jul y ,	 1981).
Da Costa,	 J.M.	 1980,	 Ph.D.	 Thesis,INPE.
Haymes, R.C.; Walraven,
A.;	 Nall,	 R.1).;	 Djuth.	 F. T. and Shel-
ton,	 D.H.	 1975,	 fi..J.	 =e:tte r	 ,	 201,
593.
Leventhal, M.; MacCallum C.J. and Stan;;,
P.D.	 1978,	 t1	 .J.	 Lette.ro, 225, 1.11.
Mandrou, P.;	 Bui-Van, N.A.;Vedrenne, G.
and Niel. M.	 1980, An.J.,	 237,	 424.
Stecker, F.W.	 1971, in Coonio Garwia Rays,
NASA SP-249, p.	 167.
r
It
t
c
c	 e
r
•	 SaoKObM	 - otRLOWN
s •o^^
1
g
&S
V
X01-_^__ `^_ "".`_•_-'^'^'. _-_ _•-^	 _.__-__. ._400 	 INK W11 ''so a•oo 
oo•^o c^ o0
FIG. 2. Average fluxes for background
and for the region where the GC was with-
in the field of view.
from Haymes et al. (1975), Leventhal et
al. (1978) and Da Costa (1980) and take
into account their angular field of view
to estimate the flux that our detector
would observe.
Using this procedure we calculated
an expected line flux of (6.67±0.94)x
10-3photons cm-2 s-1 , in very good agree-
ment with our measurement.
Mandrou et al. (1980) observed the
region -450<t ll <+450 using a telescope
with 900 FWHM which was launched in 1977
from Guaratingueti, Brazil. They give
an to upper limit for the 0.511 MeV
line flux as 9.7x10-3photons cm- 28-1.
Using our measurement and the fluxes
observed by Haymes et al. (1975), Le-
venthal et al. (1978) and Da Costa
(1980) and the line source assumption to
estimate the flux they would have ob-
served we get (9.2210.60)x10-3photons
em-2 9-1 . Therefore, their reported upper
limit flux is compatible with the value
i
_=


Measurement of the 0.511 MeV gamma ray line from the Galactic Center

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