Gamma ray emissions from young supernova remnants are discussed and calculated. The positron annihilation line is also calculated. Decay of charged pions in remnants cause generation of high energy neutrinos. This emission of neutrinos is reviewed. The CR origin and gamma emission from Magellanic clouds help to establish the intensity gradient in the galaxy. This gamma astronomical data is briefly discussed

Berezinsky, V. S.

Ginzburg, V. L.

Ptuskin, V. S.

English

NASA Technical Reports Server

OG 2.7-15
805
ON SOME PROBLEMS OF GAMMA-ASTRONOMY
V.S.Berezins_y
Institute for Nuclear Research, USSR Academy 09 Sciences,
Moscow
V.L. Ginzburg
P.N.Lebedev Physical Institute o_ the ?ISSR Academy of Scien-
ces, Moscow I17924
V.S.Ptuskin
Institute of Terrestrial Magnetism, Ionosphere and Radio Wave
Propagation, USSR Academy of Sciences, 142092 Troitsk, Moscow
Region, USSR
I. Gamma-emission fro m young supernova remnants. Suppose
that inside a young (with an age ts_lOVs) remnant of mass _
_,I M_which is expanding at a velocity u _-IO _ /s there exists
a CR_(proton) source with a power Lot and a damping time _" >>
>>I07s. Such a source of accelerated particles may be a pulsar
or turbulence inside the remnant itself. Generation of various
emissions in young remnants was discussed in /I-S/. Undergoing
nuclear interactions in a remnant, protons generate secondary
particles (electrons, positrons, _-photons and neutrinos)
through q[-meson decays.
Let protons with a spectrum
be injected into a remnant (or accelerate inside it). Bere E
is the kinetic energy of a proton_ we assume below Eo=0.4 OeV.
The secondary _-emission that occurs in this case freely le-
aves the remnant if its thickness is smaller than the radiati-
on length Xra d (63 g/ca 2 for a hydrogen medium, 93 g/ca 2 for a
helium medium). This condition is fulfilled if the remnant age
a t,zx,,-,,:a') . LM/ [-E/ k X,-.,i/
The emission occurring in _[_ 2_ decays is effectively gene-
rated while the salter thickness passed by the relativistic
proton before it ]eaves the remnant i_ suffucuently largel
X_ XN , where XN _ _WpZ-,_p _ 70 g/ca , _p _ 3 IO-2bcmZ is
the inelastic pp interaction cross-sectlon. If protons stay
in the remnant for a time T_ts, the thickness passed by them
is more than the nuclear thickness, in t_e case
(for more details see ZI/). The total number of secondary _ -
photons emitted by the remnant for the time tN for the proton
spectrum (I) turns out to be equal to
OG -15 
3 5 
 E BLE~S  MA-ASTR NOMY 
. .Berp.zinsky 
sti.tute  uclear esearch,  cademy of i.ences, 
oscow 
. . inzburg 
. .Lehedev hysical I sti.tute f t  nS 'R cademy f cien-
s, oscow I q24 
.S.Ptuskin 
stitute f e restrial aqnetism, osph re  adio ave 
r pagation,  cademy f ciences, 092 roitsk, oscow 
egion, TJ SR 
I. Ga ma-emission from young supernova re nants. Suppose 
t at i.nside a ung ( i th a  e t ': rO's) r nant f ass IS "V 
'V I .which i  panding t a elocity  ..wI " /  t re ists 
  (proton) urce ith  er cr d  ping ti e '7:: » 
» I07s • Such a source of accelerated particles ay be a pulsar 
r r ulence side e nant elf. eneration f arious 
e issions in young re nants as discussed in /1-5/. ndergoing 
uclear i teractions in a re nant, rotons enerate secondary 
articles ( lectrons, ositrons, ~ -ph tons a d eutrinos) 
ugh 1f -meson ecays. 
et rotons, ith  ectrum -t 
Np (lz):: Ll- i) (Q - ;t) ~ (~c T i ) ( I) 
be injected into a remnant (or accelerate inside it). Here  
is the kinetic energy of a proton: we assume below Eo=0.4 GeV. 
The secondary ~ -emission that occurs in this case freely le-
es t e re nant i  it  t i kness i  s aller t an t e r diati-
on length rad (63 g/cm2 for a hydrogen edium, 93 g/cm2 for a 
helium medium). This condition is fulfilled if the remnant age 
( Jf«. rAi )¥'r j 1/2 t S > tx = 3Ml -) ':: 2,8'/0 _1'\ tlQ..)(Ml )d(2) 
.. 41r tt l-r-i4J ~\') z.. ''"ad 
The em1SS1on occurrlng 1n 1Ic4> 2t decays 1S effectively gene-
rated hlle.,thematter thickness passed by the relativistic 
pr~ton before it leaves. the remnant i~ suffucuently ~arge~ 
OX "'X/II ' where 'Xi" ~ m p 6"rp'~ 70 g/cm , ~r" ~ 3 10 26cm is 
the inelastic pp interaction cross-section. If protons stay 
in the remnant for a time T ~ts' the thickness passed by them 
is ore than t e uclear t ickness, i.n the case 
1:,.(. ,t/v ':;;, ( ~Mc _ \ 1f~ .~ 10 f IJA )1/z.(lE-9) '3/-L (.to \ if2.g. (3) 
'B1Tti3 XIV J ~-Mc.? 1J XN ) (for more details see 11/). The total number of secondary r _ 
photons emitted by the remnant for the time tN for the proton 
spectrum (I) turns out to be equal to 
https://ntrs.nasa.gov/search.jsp?R=19850025675 2020-03-20T18:05:48+00:00Z
OG 2.7-15
3O6
_ere 4.._ 0.5 is the fraction of energy kept by the nucleon
after collisionT the quantity in brackets is the total number
of protons injected into the remnant; the values of _are
tabulated below for different [ (inclusive Tf_ -meson genera-
tion cross-sections are used),
2.1 2.2 2.3 2.4 2.5 2.6
_,_ 0.24 0.22 0.20 O.19 O.17 O.16
For the luminosity of the remnant and for a photon flux
from it we obtain from (4) (2.1 __ _ __ 2.6T R is the distance
to the source), ( _ ) -_t,.lao
(s )
Thus, for Los '_ IO38erq/s a young supernova remnant in the
Galaxy (R _ IO _pc) is a detectable _-source in the interval
from t_ _ I to tN -- 5 months after a flare. An account taken
of the-electron component increases the flux (5).
Note that if such remnants are main sources of galactic
CR, the required value of Lcr, depending on the value of adi-
abatic CR energy losses varies from Lcr ,_ IO_3erg/sec in the
model /I/ to Lcr _ 5 IO41erg/sec in the model /4/ (it is also
noted in /4/ that young remnants can also be the main sources
of antiprotons observed in CR). For Lcr _ IO43erg/s the dis-
cussed _ -emission could be registered by detectors of the ty- o
pe of those planned for the GRO station in the case of flares
in other galaxies.
2. Annihilation line. Positrons which occur in a rem-
nant under _+ meson decays are decelerated (outside the ac-
celeration region), annihilate and give the line E[ = O.511
MeV.
For th_ remnant age ts exceeding the recombination time
tr = 3.4 IO s the longest positron deceleratlon stage is the
process of ionization losses from the critical energy Ec (de-
termined in the cascade theory) to the.nonrelativistic energy. _
In this case- _ = b _ 2 MeV/g.cm -z. The thicknes within
which there occurs deceleration zs xb = Ec/b. The respective
age of the remnant for which the positron decelerates down to
the nonrelativistic energy is given by (for a hydrogen rem-
nant Ec = 350 MeV, for a helium remnant Ec = 250 MeV) z
G -15 
06 
. / I ) 2 rrr e (~-2 I.~,-.I:!!:) N~ 1£'1:> 00 M~ V ;:: - (4) 
" .1-J.~-i ~-i I3. t 
Here ~ ~ .  is the fraction f energy kept by the nucleon 
fter llision: t e uantity i  rackets is t e t tal nu ber 
f r tons i jected i t  t  re nantr t  lues f ~~~are 
ta ulated below f r ifferent r (i clusiverrc - eson enera-
 ro s-sections re sed): 
.I 
0.24 
.  
0.22 
.  
0.20 
.  
0.I9 
.  
0.17 
2.6 
0.I6 
or t  l inosity f t  r nant d f r  oton fl  
from it we obtain from (4) (2.1 ~ r ~ 2.6: R is the distance 
to the source) I (' 3~ ) .1 N({(;i~IODMeV)'~@\3d-2/~).i04() Lu lloerj/:1 S· I . ''l 
- - ~) Nt ( -6(L /' '3! \(,~~ (5) 
'r ~ l E~ ~ IDD Me \j ::kirRl. 'X i, i -,2. if)' to q- to erJ/S ) R. )Ch\~ 2. S ·1 
Thus, for Lcr .~ r0 38erq/s a young supernova re nant in the 
alaxy (R "'" 10 J<"pc) is a detectable ~ -source in the interval 
from tt ~ I to tN - 5 months after a flare. An account taken 
f t e electron co ponent i creases t e fl  ( ). 
ote that if such re nants are ain sources f alactic 
CR, the required value of Lcr, depending on the value of adi-
abatic CR energy losses varies from Lcr ~ro43erg/sec in the 
odel / / t  cr~  Io4Ierg/sec i  t e odel / / it i  ls  
oted i  / / t at ung re nants ca  lso e t  ain s urces 
of antiprotons observed in CR). For !'cr I'- I043erg/s the dis-
cussed ~ -e ission could be registered by detectors of the ty-
e f t se pla ned f r t e O st tion i  t e se f fl res 
i  ther alaxies. 
2. nnihilation line. Positrons which 
ant under 'Tr+ eson decays are ecelerated 
celeration region), annihilate and give the 
eV. 
occur in 
( utside 
line E'I 
a re -
t  -
= O.SII 
For thg remnant age ts exceeding the recombination time 
tr  3.4 IO s the longest positron deceleration stage is the 
process of ionization losses from the critical energy Ec (de-
ter ined in the,~ascade theory) to the2 nonrelativistic energy. 
'In this case - ~ = b ":Ie 2 MeV/g.cm- • "["he thicknes within 
which there occurs deceleration is xb = Ec/b. The respective 
age f the re nant for hich the positron decelerates do n to 
the onrelativistic enerqy is given by (for a hydrogen re -
nant Ec = 350 MeV, for a helium remnant Ec = 250 MeV) t 
t () .= I 3 /'II<. E _ \ if: b It. \ •• J~ (tl Y" l' \ c' g \ '12. (3 SO \ l/1 
o \'81rti~Ec) I v M~} 17) ~EcJ $ (6) 
OG 2.7-15
307
A nonrelativistic positron annihilates more rapidly.
A positron decelerated by the moment
I _ _ _ _ (_ _ _ _A_'_ '_ ( _ _ _ _0_ _'_/_ /'_" _ _i_=,, _ =_,3.1o I_ t_ _ |_} (7)t,/_¢,/ ', 1._ - \ =( _ 2_ 2
annihilates within the remnant. Here _.¢= Et-_z-2.5 IO- _cm ,
NA=6 IO 23. Hence, the effective emission annihilation lasts
from t -_ I to tb_ 3 months. The total number of annihilation
photons emitted for this period is described by a formula ana-
logous to (4) ( q_, _ _.2 _),
_ , - J g-_'. E_ ( /_
The estimate for the flux F_(E_=O.5 MeV) colncides approxima-
tely with (5).
The possibility to observe an annihilation line depends
on the emission level in a continuum which is created by se-
condary positrons and electrons in the remnant. (It can be
easily estimated that if all primary and secondary CR do not
leave the remnant, the generation power _-e _ of the compo-
nent is about Lcr/6 and the annihilation line takes up 2 IO _
Lcr. A further calculation of the background near E =O.5ITM_I/
depends on the values of the magnetic field and of the ther-
mal radiation density in the remnant). _f_ however, the whole
remnant is involved in the effective CR acceleration, the ener-
gy losses of positrons may prove inessential and the estimate
(8) will be largely overestimated.
3. Emission of neutrinos. Decay of charged p£ons in a
high-energy neutrinos. In this
remnant causes generation of _ (_I'_" _r p- _" _" , (9)
2.2 2.3 2.4 2,5 2.6 2.7 2.8 2.9 3.0
I03(qv+_h) 94.6 69.8 51.9 38 I 29.7 22.8 17 7 I3.8 'IOe9
_ • •
Neutrino emission starts at the moment tlr(E) beginning from
which pious with the Lorentz-factor _ decay at the length of
their free path (_.Eis the cross-section of'/$-N scattering,
is the lifetime of a resting pion)s (,o,k4_r m_--u_ / IOz [
The bright phase ends at ts_,t N.
To detect neutrinos, it is convenient to use muon pro-
duction in the reactions V_ + N-_ +_ underground around the
underground muon detector. At E./_>_ 30-50 GeV the muon keeps
the direction of the parent neutrino, which indicates the di-
rection to the source. Transparency of the Earth for neutrino
with E v =IO-IO3GeV makes it possible to eliminate the backgro-
und of atmospheric muons.
The number of muons which are produced by interaction bet-
ween neutrinos and ground nuclei and which passed through a de-
G .7-15 
07 
 onrelativistic sitron nihilates ore pidly. 
A positron decelerated by __ the oment _ 
t = (3f'J\do G IVA \*: . '1-(M )~lz. (!Q.~ \'3/i ('3';O)i/t. (7) 
AI\,. <6.;>.,) .-3,310 M ) l"" 
c::t1'u f!) 1.1 c::c: 52 
annihilates ithin the re nant. ere ~c= Tr\l=2.s I - c , 
NA=6 I023. ence, the effective e ission annihilation lasts 
from t "-' I to tb'V 3 onths. The total number of annihilation 
otons itted f r t is eriod i  escribed  a f r ula a-
logous to ( 4 ) ( If''ff't ~ 1.2 'i" uC ) I . 
Nt(£X= 01 SH fits") ~ 2fltt (i-J.. ~~1-ti, ~. ~ ·tt-~ -t¥) (8) 
The estimate for the flux F~(EX=O.s MeV) coincides approxima-
tel  ith ( ). 
he o sibility t  serve a  nihilation li e epends 
n t  e ission l el i  a c nti um hich i  reated  s -
ndary ositrons d l ctrons i   nant. t   
easily esti ated t at if ll pri ary and secondary CR do not 
leave t e re nant, the eneration po er e-e+ f t e co po-
nent is about L r/6 and the annihilatton line takes up 2 IO~ 
JJcr.  f rther calculation f the background near E =0. sI!M~V 
epends on t  lu~s f t e agnetic fi l  a d f t e t er-
al radiation density in the re nant). If, however, the whole 
nant  olved   ffective  celeration,  er-
gy losses of positrons may prove inessenti.al and the esti ate 
( ) ill e l r ely erestimated. 
. ission f eutrinos. ecay f arged i ns i  a 
remnant causes generation of high-energy neutrinos. In this 
case N - (t)dE = (If (f;_). ~(!~!). ~ .(€ )-~ d£ 
Y,.tl-',.. 11",,+ Tv!'" i-.J..V ~c E t E, (9) 
~ .  .  .  p S .  .  .  . . .  
I03(~II ... +~~) 94.6 69.8 sI.9 38.1 29.7 22.817.7 .I3.8 ·10.9 
Neutrlno remission starts at the moment t.'tt'(f} beginning from 
hich i ns ith t e orentz-factor r cay t t  l gth f 
their free path (Z.tr is the cross-sect ion of 'ltN scattering, 
is th~ lifeti e of a resting pion). 
i (' r\ ::: (""3 M <!53C c 't":rr )'1/ '!, r i/'3 _ C • '2 fll \113 (\ 09 ) ,- 1(~ 
11"") J ." - L::)· 10 M - S ~ 7r Wlrr 'U Y 1"\ ¢ I \.l 
1J1he bright phase ends at ts ..... t . 
(ro) 
o etect eutrinos, it i  c nvenient t  se uon ro-
duction in the reactions Y"" + N -?' r + X underground around the 
underground muon detector. At Er- ~ 30-50 GeV the muon keeps 
t e irection f t  arent eutrino, hich indicates t  i-
rection t  t e s urce. ~ ansparency f t e arth f r eutrino 
wi th E V =10-103GeV makes it possible to eliminate the backgro-
d f at ospheric uons. 
he ber f uons hich re r duced  i teraction et-
een neutrinos and ground nuclei and hich passed through a de-
OG 2.7-15
3O8
tector of area S for the time tN is eqhal to (the inclusive
cross-sections Y_ + N-_ +_ are used in the calculations, the
values J<_(E) are tabulated). _[>E#)= K_ _i0kp_/_)_.(Z_r/f0_er_/_).
[li00  l-(.NI °
G@V _ 2:1 2.2 2.3 2.4 2.5 2.6
30 40 2T 8.8 3.5 ]_.4 0.54
zoo 36 Z9 7.7 2.9 Z.I 0.4_
zoo0 22 IO 3.7 1.3 0.4_ O.14
Thus, the existing underground muqn detectors (S=I25 m z)
can register high-enerffv neutrinos from a young SN remnant in
our Galaxy for Lcr> _ IO4_/erg/s. _
4. The CR oriqin and _-emission from Maqel!anic Clouds. The
gamma-astronomical data make it possible to establish the CR
intensity gradient in the Galaxy. But the available results
are contradictory /7,8/. Zf, according to /7/, in the gamma-
range of 300 MeV_E< 5 GeT _he radia1_ive oapa0it_ is really
constant up to the distances R_20 Epc from the galactic cen-
tre, the CR halo must be very large. Then a rather effective
reflection of CR would occur at the halo boundaries (CR are
now assumed to go_freely out of the halo /9/). The results of
/7/ conform to the metagalactic model of the origin of the CR
proton-nuclear component. We believe, as before, /IO/ that
metagalactic models are impro_ble _th[s does not refer to CR
with a very high energy E>_IO--IOZ_eV). Metagalactic models
can be verified by measuring gamma-luminosity from Magellanic
Clouds /_,4/, The most reliable and weakly depending on dif-
ferent assumptions is in this case the measurement of_=_¢/_ad
the ratio of gamma-lumlnosities of the Small and Large Magel-
lanic Clouds, say, for E_>IO0 MeV. In metagalactic models /% :
=0.56-0.68 depending on the value of the mass of the Clouds
used /4/. Respective measurements can be carried out only
with the help of the next generation of gamma-telescopes.
_Re ferences
I. Berezinsky V.S., Prilutsky O.F. !978 Astron.Astroph.,66,
325.
2. Gavallo G., Paccini F° I980 Astron.Astroph.,88, 367.
3. Chevalier R.A. I982 Ap.J., 259, 302
4. G_nzburg V°L., Ptuskin V°S. 1984 J.Astrophys.Astron.(In-
dis), 5,99.
5. Chevalier R.A. lq84 Ap. J., 285, L 63.
6. Beresinsky V.S., Volgusky v.v. I979 T6 TCRC, If), 326.
7. Bloeman J.B.G.M.et al. I984 Astron.Astrophys.,I35, 12.
8. Bhat C.L. et alo _984 Astron.Astrophys., I40, 284.
9. Astrophysics of Cosmic _ays, ed. V,L.G%nzburg, Nauka,lq84
70.Ginzburg V.L. Phil.Trans.Roy.Soc. _974 A277, 463.
II.Ginzburg V.L. I972 Nature, Phys.Sci., 239, 8.
OG 2. 5 
30  
te t r f ar  S f r th  tim  tN is ual t  (th  in l sive 
cross-sections Y}o; + N -'? f + X are used in the calculations, the 
values J<'t(E) are tabulated) I n,... t~E,M)~ KK (1D kpc/R)Z. (Lc,)I042-era/3). 
E,v. 'l~/iOOM2). (iN /10tS) (II) 
e  X  .. I .  .  .  .  .  
  2 I 8 .8 3 • 5 I • 4 0 • 54 
100  1  .  .  1.1 . 1 
1000  10 .  1.  . 1 0.  
Thus, the existing underground mu~n detectors ($=125 m2.) 
can re ister high-energy neutrinos fro  a young SN re nant in 
r alaxy f r cr ~ IO'1L /s. ' 
4. The CR origin and X-emission from ~1aqellanic Clouds. The 
a ma-astronomical t  ake it ssible t  t blish t   
i tensity radient i  t e ,alaxy. ut t  ailable r sults 
are contradictory / ,8/. If, according to / /, in the ga ma-
range of 300 ev<:K <: 5 GeT the radiative capacity is really 
c nstant up t  t e istances "-' 20 Kpc fro  the alactic cEm'"!! 
, t   lo ust  ery l r e. en  t er fective 
r flection f  ould ccur t t e alo oundaries (  are 
 ss ed t  _freely t f t  lo / /). he r sults f 
/ / conform t  t e etagalactic odel f t e rigin f t e CR 
proton-nuclear co ponent. e believe, as before, /10/ that 
metagalactic models are improy,ble ~this does not refer to CR 
i th a very high energy E *' IO°' _101 eV). etagalactic odels 
can be verified by easuring ga ma-luminosity from agellanic 
louds /tt,4/. The ost reliable and eakly depending on if-
ferent assumptions is in this case the measurement of A,::, ~c/~I\C:' 
the ratio of ga ma-luminosities of the S all and Large agel-
lanic Clouds, say, for Ea>IOO MeV. In metaga1actic models 6 = 
0.56-0.68 epending  t e alue f t e a s f t e louds 
used /4/. Respective measurements can be carried out only 
ith the elp f the next generation f ga ma-telescopes. 
eferences 
I. Berezinsky V.S., Prilutsky O.F. 1978 Astron.Astroph.,~, 
25. 
2. Gava110 G., Paccini F. 1980 Astron.Astroph,.,88, 367. 
3. hevalier R.A. I982 p.J., ~  302 
4. i.nzburg .L., ptuskin .S. I984 J .Astrophys.Astron. (In-
ia), 1, 9. 
5. hevalier R.A. Iq84 Ap. J., ~  °L 63. 
6. Beresinsky v.S., Volgusky v.V. I979 16 TCRC, ~, 326. 
7. Bloeman J.B.G.M.et a1. 1984 stron.Aatrophys.,l1i, r2. 
8. Bhat C.L •. et ~l. 1984 stron.Astrophys., !!Q, 284. 
9 8 strophysics of Cosmic Rays, ed. .L.G{nzburg, auka,IQ84 
lO.Ginzburg V.L .. Phi1.Trans.Roy.Soc. yQ74 illl, 463. 
II. inzburg V.L. 1972 ature, Phys.Sci., ill, 8. 


On some problems of gamma-astronomy

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