V O L U M E 22, N U M B E R 11 PHYSICAL REVIEW LETTERS 17 MARCH 1969

7D. Ashery , N. Bahcal l , G. Goldring, A. Sprinzak, and Y. Wolfson, Nucl. Phys . A101, 51 (1967).

8I. Ben Zvi , P . Gilad, M. Goldberg, G. Goldring, A. Schwarzschi ld , A. Sprinzak, and Z. Vager , Nucl. Phys . A m , 592 (1968).

9 F . S. Stephens, N. La rk , and R. M. Diamond, Phys . Rev. Le t t e r s 12, 225 (1964); R. M. Diamond, F . S. Stephens, and W. J . Swiatecki, Phys . Le t t e r s 2 i , 315 (1964).

10A. S. Davydov and A. A. Chaban, Nucl. Phys . 20j 499 (1960).

U A. S. Davydov and V. I. Ovcharenko, Yadern. F iz . 3̂ , 1011 (1966) [ t rans la t ion : Soviet J . Nucl. Phys . _3, 740 (1966)].

12Y. Yoshizawa, B. Elbek, B. Herskind, and M. C. Olesen, Nucl. Phys . 73 , 273 (1965).

13G. C. Seaman, J . G. Greenberg , D. A. Bromley , and F . K. McGowan, Phys . Rev. .149, 925 (1966).

Recently Clark, Garmire, and Kraushaar1 have reported a definite flux of high-energy (~100-MeV) extraterrestrial gamma radiation. This ra­diation has been detected from a band in the sky coincident with the galactic plane and the intensi­ty has a broad maximum towards the galactic center. In addition there also seems to be evi­dence for an isotropic component which is be­lieved to originate outside the galaxy. In this note we shall briefly discuss a possible new source of this radiation.

As pointed out by Clark, Garmire, and Krau­shaar,1 the expected intensity of the radiation arising from the decay of neutral pions produced in collisions of cosmic-ray nucleons with inter­stellar matter is smaller, by a factor of ~25, than the observed intensity in the direction of the galactic center. In this calculation they have made the valid assumption that the mean inter­stellar flux of high-energy cosmic-ray nuclei is the same as that observed at the top of the earth's atmosphere during solar minimum. According to the present ideas of cosmic-ray modulation the interstellar flux at energies above -1 GeV/nucle-on, where pion production becomes significant, cannot be more than a factor of 2 higher than the

14J. Fink and P . Kienle, Phys . Le t t e r s JL7, 326 (1965). i 5D. Yeboah-Amankwah, L. Grodzins , and R. B.

F ranke l , Phys . Rev. L e t t e r s _18_, 791 (1967). 1 6P. Steiner , E. Gerdau, P . Kienle, and H. J . Korner ,

Phys . Le t t e r s 24B, 515 (1967). 17U. Atzmony, E. R. Bauminger , J . H e s s , A. Mus ta -

chi , and S. Ofer, Phys . Rev. Le t t e r s 18, 1061 (1967). 1 8 P. Kienle, W. Henning, G. Kaindl, H. J . Korne r ,

H. Schal ler , and F. Wagner , J . Phys . Soc. Japan 24, 207 (1968).

19S. Bernow, S. Devons, I. Duerdoth, D. Hitlin, J . W. Kast , E. R. Macagno, J . Rainwater , K. Runge, and C. S. Wu, Phys . Rev. Le t t e r s .18, 787 (1967).

2 0T. Udagawa and R. K. Sheline, Phys . Rev. Le t t e r s JJ., 325 (1966).

2 1E. R. Marsha lek , Phys . Rev. Le t t e r s 2£, 214 (1968). 22F» S. Stephens, R. M. Diamond, W. H. Kelly, J . O.

Newton, and D. Ward, to be published.

solar-minimum flux; therefore, nuclear colli­sions may not provide more than about ^ of the observed flux of gamma rays. On the other hand, as shown below, the high-energy electron compo­nent of cosmic rays may well provide a source of these hard quanta if the high-intensity microwave radiation in the wavelength interval of 0.04-0.13 cm observed by Shivanandan, Houck, and Har-wit2 is confirmed. The intensity of the new mi­crowave radiation is 5X10""9 W cm""2 s r" 1 , which corresponds to an energy density of 13 eV/cm3 with a maximum photon energy of 3 x lO" 3 eV. Since this radiation seems to be fairly isotropic one may assume that it pervades a spherical volume which at least envelops the whole galaxy.

The differential spectrum of cosmic-ray elec­trons as observed by Anand, Daniel, and Ste­phens3 is

F(E ) = 905/£ a-64 cm"2 s ec" 1

e e

sr""1 MeV"1. (1)

The differential intensity of the scattered photons arising from the inverse Compton effect is given

POSSIBLE ORIGIN OF HIGH-ENERGY COSMIC GAMMA RAYS?

R. Cowsik and Yash Pal Tata Inst i tute of Fundamental R e s e a r c h , Bombay, 5 , India

(Received 17 December 1969)

The intensity of the new microwave radia t ion observed by Shivanandan, Houck, and Harwit i s adequate to produce , by Compton sca t t e r ing on c o s m i c - r a y e l e c t r o n s , the flux and dis t r ibut ion of ~100-MeV y r a y s repor ted by Clark , G a r m i r e , and K r a u s h a a r .

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VOLUME 22,NUMBER 11 P H Y S I C A L R E V I E W L E T T E R S 17MARCH 1969

by

7

XNvL c m * 2 s e c " 1 s r " 1 MeV" 1 , (2)

where m i s the m a s s of the e lec t ron in MeV, e i s the mean energy and N the number density of the microwave photons, a y the Thomson c r o s s sect ion ( 6 . 6 5 x l O " 2 5 cm2) , and L the effective d is tance in the di rec t ion under considerat ion. The in tegra l intensity of y r a y s then becomes

/ ( £ ) ^ 3 x l 0 - 2 £ 0 - 8 2 c m " 2 s e c " 1 s r " 1 . (3) y

Taking L =7 xlO2 2 cm towards the galact ic c e n ­t e r , the expected intensity i s ~5xlO""4 cm""2

sec""1 sr""1. The a r e a - s o l i d - a n g l e product for the de tec tor used by Clark , Gar m i r e , and K r a u -shaa r 1 i s given a s 0.5 cm2 s r . Assuming that the g a m m a - r a y flux i s approximate ly i so t ropic over the 15° opening angle of the te lescope we expect a counting r a t e of ~ 2 . 5 x l 0 ~ 4 s e c " 1 , a s compared with the observed counting r a t e in th is d i rec t ion of ~4xlO"~4 s e c " 1 given4 in Fig. 3 of Clark, G a r -m i r e , and Kraushaa r . 1

It has been pointed out by Hayakawa5 that with changing galact ic longitude the g a m m a - r a y i n ­tensi ty v a r i e s in the s ame way a s the intensi ty of the 21-cm hydrogen line, thus indicating a cor re la t ion of this radiat ion with m a t t e r in the galaxy. If the in te rpre ta t ion given h e r e for the or igin of the h igh-energy g a m m a r a y s i s c o r r e c t , then the i r intensity dis t r ibut ion would ref lect the c o s m i c - r a y e lec t ron dens i t i es in va r ious reg ions of the galaxy. It i s pe rhaps reasonab le that c o s -

T h e r e i s at p resen t an inc reas ing number of meson and baryon r e sonances whose exis tence is clouded by the fact that they may also be i n t e r ­pre ted a s a r i s i n g from some kinematic effect r a t h e r than being t rue r e s o n a n c e s . The most studied yet pe r s i s t en t ly bewildering one in this ca tegory i s the Ax meson, a pn enhancement at

m i c - r a y e lec t ron density should be co r r e l a t ed with ma t t e r density and a l so with magnetic field s t rength .

Regarding the poss ib le i so t ropic component of these hard quanta, it i s to be pointed out that a c o s m i c - r a y halo with a d i ame te r of ~1023 cm could very well r ep roduce the observed var ia t ion of g a m m a - r a y intensity with galact ic lati tude. There fore , one has to wait for the accumulat ion of m o r e data before the exis tence of an e x t r a -galact ic component can be well es tabl ished.

We would like to point out that a microwave radia t ion of the intensi ty r epor t ed by Shivanan-dan, Houck, and Harwit2 would produce , through inve r se Comtpon effect, a flux of 100-MeV g a m ­ma r a y s from the Crab nebula, which i s sma l l e r , by a factor of ~10, than the l imit of ~5 x 10 " 5

cm""2 sec""1 r epo r t ed by Clark, G a r m i r e , and Kraushaa r . 1

kj . W. Clark, G. P. Garmire, and W. L. Kraushaar, Astrophys. J._153, L203 (1968).

2K. Shivanandan, J . R. Houck, and M. O. Harwit, Phys. Rev. Letters 21, 1460 (1968).

3K. C. Anand, R. R. Daniel, and S. A. Stephens, Phys. Rev. Letters 20, 764 (1968).

4Clark, Garmire, and Kraushaar (Ref. 1) have quot­ed their result in terms of a line intensity of ~5x 10""4

cm" 2 rad . Their detector, which has an area-solid-angle factor of 0.5 cm2 s r , has a geometry factor of 0.8 cm2 rad for a line source. Therefore in terms of line intensity our calculation would give ~3x 10-"4 pho­tons cm"2 rad" 1 in the direction of the galactic center.

5S. Hayakawa, in Colloquium on Cosmic Ray Studies, Tata Institute of Fundamental Research, November, 1968 (to be published).

about 1080 MeV, with a width around 100 MeV and UPG = 1 1 + " . It has long been pointed out1

that this enhancement could a lso be due to a Dre l l -H i ida -Deck - type k inemat ic effect (hereaf­t e r r e f e r r e d to a s the Deck effect). A recent mul t iper iphera l Regge calculat ion by Berge r 2 in the s ame sp i r i t a lso fits the exper imenta l data

A KINEMATIC-AMBIGUITY-FREE TEST F O R ^ AND B MESONS*

Rober t T . P o e , t Bipin R. Desa i , Anne Kernan, and Harvey K. Shepard Department of Physics, University of California, Riverside, California

(Received 6 January 1969)

The photoproduction reaction channel yn ~*piT+iT~"irm~ is suggested as a means to test whether the A± and the B mesons are genuine resonances or kinematic effects. Implica­tions for the duality principle are discussed.

551