38

COSMIC NEUTRINO FLUXES -- SCALING FROM UHE GAMMA RAYS

Michael L. CherryDept . of Physics and Astronomy, Louisiana State University, Baton Rouge, LA 70803 USA

Nuclear Physics B (Proc. Suppl.) 14A (1990) 38-46North-Holland

Gamma ray and neutrino observations are closely coupled : in energetic astrophysical objects wherecopious production of pions takes place, both gammas and neutrinos are produced . Although y rays canbe produced as a result of either electron or hadron acceleration processes, however, the neutrinos area clean and unequivocal tracer of the hadrons . Assuming that UHE y rays are produced by energetichadrons in astrophysical "beam dumps", it is possible to estimate fluxes of cosmic neutrinos based onthe UHE .y ray observations . These estimates are made for Cygnus X-3 and applied to a variety of othersources . Throughout, an attempt is made to parametrize the results so that they can easily be normalizedto other detector areas or UHE -f ray fluxes, and so that they can easily be modified for more or lessoptimistic assumptions about gamma ray attenuation and relative v -- y intensity levels.

1 . IntroductionOur information on energetic hadron production in

cosmic sources comes from direct cosmic ray studies andgamma ray observations . The interpretation of chargedcosmic ray measurements is complicated, however, bythe presence of the galactic magnetic field, which makesisotropic the arrival directions of all but the highest en-ergy particles, and by the production of secondary par-ticles in interactions with the interstellar medium. Mea-surements of gamma ray lines at low energies (near 1MeV) give direct evidence of proton acceleration to MeVand GeV energies in active regions on the sun, in theearth's atmosphere, and toward the galactic center' . Andat energies of 50 MeV to 10 GeV, the diffuse gamma rayemission from the galactic disk can be modeled as a com-bination of an electron component (due to bremsstrah-lung, synchrotron and Compton emission, and pair pro-duction in the interstellar medium) and a pro meson decaycomponent z .

At very high energies (VHE, 100 GeV to 100 TeV),binary neutron stars, individual pulsars, and the radiogalaxy Cen A have been detected sporadically, but atthese energies there is no obvious way to separate theelectron and hadron components of the signal'' . At ul-trahigh energies (UHE, 100 TeV to 100 PeV), however,

0920-5632/90/$03.50 O Elsevier Science Publishers B.V .(North-Holland)

where positive signals have been reported from four bi-nary neutron stars and the Crab pulsar s, ", energy lossesgenerally proceed too rapidly to allow the required accel-eration of electrons . Although special geometries and thecurvature radiation model of Cohen and MustafaP mayprovide a plausible electron mechanism, the usual pic-ture is that the UHE emission is presumably due to highenergy hadrons .

The only alternative to the UHE -y rays as a tracer ofPeV hadrons is the high energy neutrino emission fromcharged meson decay. If the UHE gamma ray emissionis due to 7r" decays, then the corresponding 7r -ß -decay vflux must be comparable to or larger than the gammaray flux, and can be calculated straightforwardly. Scal-ing from the gamma ray measurements allows us to pre-dict expected v flux rates with some reasonable degree ofconfidence . Observation of the neutrinos then will pro-vide the clearest and most unambiguous measurementswe have of high energy cosmic hadrons at their source .

High energy air showers, presumably from 10" to2 x 10"' eV photons, were first detected 7,H with the char-acteristic 4 .8 hr orbital period from Cygnus X-3 in 1976-80, and since then signals have been reported from threeother binary x-ray sources (Her X-1`'-12 , Vela. X-1", and

LMC X-41 '1 ) and the Crab Pulsar" . Neutron stars havelong been recognized as attractive sites for the accelera-tion of exceptionally energetic cosmic rays, and the highproportion of interacting binary star systems on the listof UHE emitters strongly suggests that the UHE luminos-ity is fed by accretion' . Although the acceleration mecha-nism is poorly understood, the production of high energyphotons (and th:-~ accompanying neutrinos) is straightfor-ward if a beam of energetic protons accelerated at theneutron star is allowed to strike either the atmosphereof a companion star or an accretion wake or tail stream-ing behind the neutron star" . At those points in theorbit where the target material lies between the neutronstar and the earth, and where the accelerated beam isdirected toward the earth, episodes of 7r°-decay photonemission and a}- and Ft}-decay neutrino emission canbe expected .

The emission in the HE, VHE, and UHE ranges ap-pears to be highly sporadic both in time and in phase .Above 100 MeV, SAS II reported a 4o- signal from CygX-3 in 1973", but COS B could provide only upper limitsin 1975". At VHE energies, Cyg X-3 has been detectedsometimes in the range of binary phases 0 - 0.15 - 0.3,at other times near phase 0 .5 - 0.7, and at some timesnot at all . At UHE energies, at least through 1985, thesignal has been detected near phases 0.25 or 0.6 1" . Since1986, Cyg X-3 has generally been undetectable (althoughthe CYGNUS experiment2" has reported a brief periodof activity in April-May 1986, and Fly's Eye21 has pre-sented evidence for a 10 18 eV signal during the period1981-1988) . In general, the emission has not been seenjust before or after- eclipse (,0 = 0) or simultaneously atboth low and high phases (as would be expected if thetarget were the limb of the companion's atmosphere) . Inthe case of the VHE signal from Her X-1, emission hasbeen seen over the entire orbital period including duringx-ray eclipse)" . The implicaticn is that the photons (andcorresponding neutrinos) produced by highly relativisticprotons interacting in the environment of a closely or-

M.L . Cherry/Cosmic neutrino fluxes

biting binary star system are generated in a turbulent,non-static medium where the geometric conditions re-quired for a detectable signal are not neatly reproducibleor always satisfied .

In Sec . 2, neutrino fluxes are estimated based on themeasured gamma rays . These neutrino (and neutrino-induced muon) fluxes are normalized by the proton lu-minosity at the source in Sec . 3, and in Sec . 4 these esti-mates are extended to several varieties of specific sources .Finally, in Sec . 5, the potential for simultaneous y ray-v observations is discussed, including the possibility fordetecting neutrino emission during transient gamma rayevents .2 . Flux Estimates - Scaling from UHE GammaRay Observations

Numerous authors22-25 have made predictions of cos-mic neutrino flux rates . The connection between the ob-served .y ray flux and the accompanying neutrino fluxis made very clearly by Kolb et al . 2s With the assump-tions that the photons are the result of 7r° decay, that thecharged 7rf mesons decay in flight before they interact,and that the K and charmed meson contributions can beneglected, then the measured UHE ,y ray spectrum

A art decay in flight produces a neutrino of maximumenergy

E,, = (I - -' ) E�M,r

and gives a resulting 7r-decay neutrino spectrum

d.5,,(

M

dE

'' )

-I

dS,C

1

,m2

E;;" �'

.2 - .4dE

4"

a

for spectral indices in the range a - 2 -- 3.

39

Kolb et alr' assume mc, !.oenergetic photons are emitted at en-ergy EA/2 . Here a flat spectrum is assumed from 0 to EA. Theresults here, and also in Eq . (4), therefore differ from theirs byapproximately a factor of 2.

dS.,"_ CE (1)

dE, '

implies a pion spectrum'

d_S,+ +.- dS,r ._=

dE,r2dE~

aCE,r" . (2)

40

In a close binary system, the neutrino emission pre-

sumably lasts through most of the time during which the

neutron star is eclipsed :

where a �(E) is a neutrino energy-dependent absorption

factor, T is the binary period, a is the binary separa-tion, and R, is the dimension of the target region (e.g.,

the radius of the neutron star's larger companion) . Theabsorption factor a�(E) may be close to unity for a rea-sonable fraction of the eclipsed4-26 . For the -y rays,

r, = a,(E)hd

(6)

where h is a characteristic dimension of the target mate-rial (e .g ., the companion star's atmospheric scale height) .For both the neutrinos and the gammas, the target mustbe thick enough (> 50 g cm-2) to generate secondarymesons efficiently. For the gammas, if the target thick-ness is much greater than -200 g cm-2 , absorption willdecrease the flux ; for the neutrinos, absorption by themain body of the companion star may set in above a fewTeV2'i . As pointed out by numerous authors23-2.1 the rel-ative v--+ duty factor A = r�/r, may be large : In the caseof the Haverah Park Cyg X-3 observations, r, /T - 0.02,so that if 25 a - 1.058, and a;,(_E) - 0.4, then A - 20t .The emitted v-decay v spectrum is then

dS� dS,dE

ti .3A(E)dE

An energetic muon produced by a neutrino interac-tion in the rock around the detector has a range

P(E) -= N.ja�R,jj

M.L. Cherry/Cosmic neutrino fluxes

R,, = 3x10'ln(1+iTV)gcm-2. (8)

The probability that a neutrino of energy E� headed to-ward the detector interacts in the rock within a distanceR,,(E) of the detector, and produces a muon which thentraverses the detector, is

This is in fact only a lower limit ifone allows for smearing ofanintrinsically narrower r, at the source . At VHE energies (where themechanism may be electronic rather than hadronic), the Whipplemeasurements give r,/T - 0.1, or A > 4.

where the v cross section is taken from Ref. 26 . The7r-decay v-induced muon event rate in a detector of areaA is then

n,,

ti

.3N,,Af A(E) dE a,�Rp dE

EA

S,(E, >_ 3 x 10" eV)ti r(a)C0.4 x 6 x 104 M2)(1.5 x 10-lacm-2sec-t )

x ( X )(1/3

- 120 fn-u~a~Pyr (10)

normalized to the observed Haverah Park Cygnus X-3flux and a detector area A = 6 x 104 m2 . (The detectorarea A = 6 x 10'm2 is taken to be that of GRANDE,since this is the largest of the proposed new detectors .The calculation can be scaled to DUMAND or any otherdetector by using the appropriate value of eA.) The func-tion r(a) is the result of the actual integration (in eventsyr- ') performed over the range 10 GeV - 1000 TeV andscaled to the case of GRANDE. It is assumed that a typ-ical Southern hemisphere source is visible for a fractione = 0.4 of the time, where the on-source duty factor E isthe ratio of the effective area to the detector's geometricarea (E is a function of the detector and source location,and the time of year.), and that the observed 10' 5 eVCygnus X-3 y ray flux has been attenuated on the mi-crowave background by a factor of 1/3 . Therange of expected rates as a function of spectral index isthen :

a

r(a) yr- '1 .5 32 502.1 902.5 20002.75 18,000

The muon rate increases rapidly with a steepening spec-trum. We have normalized to the y ray flux above 3 x 10"'eV and assumed a power law spectrum all the way downto TeV energies . Since most of the neutrino contributionarises from energies near 10 TeV, an increasing spectralindex with a fixed rate above 3 x 10 15 eV leads to arapidly increasing 10 'TeV neutrino event rate . The y raymeasurements suggest ct - 2.1 for Cygnus X-3 . 1

lit should be made clear that, although this is the usual as-

Based on Hillas' model'' of a monoenergetic 10'7 eVproton spectrum at the source, Gaisser and Stanev27 pre-dict an upward-moving muon flux above 2 GeV of 2 x10- ' 5Cm-2sec-', or 16 yr- ' in 6 x 10" M2(assuming thesame e = 0.4 duty factor) . For the same power in anE-2 proton spectrum, their results give 20 yr-', a factorof 2.5 below this estimate . These rates vary by no morethan a factor of 2 over the entire range of densities in thetarget region 10-12 to 10-6 g cm-3 .

The calculations of Berezinsky et al .23 , assuming thesame energy-independent v - -y duty factor A = 20, inde-pendently give the number of upward-moving muons in0.4 x6x~0'm2 tobe

n,,(> 10 GeV)

=

30yr-'

n,,(> 1000eV) = 24yr-'

n,,(> 1 TeV)

=

16yr-'

Again, these results are in reasonable agreement with thepresent estimates.

The normalization to Haverah Park used above is notcrucial to the argument, and has been used only for con-venience . The expected muon rate can be calculated fromEq. 10 based on any desired normalization . In the firstline of the table below, the values of n,, as a function of

sumption, such a flat spectrum is not particularly well established .At UIfE energies, Samorski and Staminr derive a = 2.2 f 0 .3 fromtheir data based on 13 events above 2 PeV and 4 events above 10PeV . In very few other cases is spectral information given in a sin-gle experiment . Rather, the results of many experiments (at both'PeV and PeV energies) are typically lumped together, based ondata taken at different times, sometimes time-averaged and some-times from transients, with different thresholds, and often no errorbars given for intensities or energy ranges ; and then a power lawspectrum is drawn through the data . Although it is difficult tosuggest a better technique, the universal adoption of such an ex-tremely hard spectrum must at least be treated with caution . Onthe other hand, the underground IMB detector is a factor of 150smaller than the proposed GRANDE detector, so the upper limitsfrom IMB rule out a stee (a :_" 2.5) steady-sta.fe spectrum at thelevel of several x 150 yr - in 6 x 10W from Cygnus X-3 .

M.L. Cherry/Cosmic neutrino fluxes 41

a based on the 1979-1982 Haverah Park flux levels fromCyg X-3 are repeated . The results are also calculated bynormalizing to the 1976-1980 Kiel flux7 and the CYGNUSresult 2" based on a 45-day period in 1986. In each casethe reported .y ray flux level S,,(> Em;� ) is given on whichthe scaling is based .

Unfortunately, although Cyg X-3 may be a reason-able standard candle for normalization purposes, it is aNorthern Hemisphere source which may not be visiblein neutrinos from Northern Hemisphere detectors. It istherefore interesting to scale to the Southern Hemispheresources LMC X-4 and Vela X-1, as well: The observedUHE flux from the Southern Hemisphere source LMCX-4 is'" 4.6 x 10- ' 5cm-2sec- ' above 10 PeV . Assuming

f,,-wave. - 0.1 here, Eq. 10 gives n,, - 150 yr- ' for a = 2,and n,, - 330 yr- ' for a = 2.1, comparable to or abovethe rates suggested for Cyg X-3 . Similarly, the Adelaidegroup'" have reported a time-averaged -f ray flux from

Vela X-1 of S7 (Ey > 3PeV) = 9 x 10- ' 5cm-2sec'' . Tak-ing = 1 for the case of this nearby source, wefind predicted neutrino-induced muon fluxes at - 20%of the level predicted for Cygnus X-3 (based on the orig-

inal Haverah Park normalization) .Summarizing the above, various theoretical mod-

els and normalizations to UHE -f ray observa-

Lions yield expected muon event rates in detec-tors of the scale currently being discussed, fromsources such as Cyg X-3 (at the level observedprior to 1986), LMC X-4, and Vela X-1, in ex-cess of ten events per year for differential spectralindices in the range of 2 to 2 .5 . The results have beenparametrized in terms of the measured UHE .y ray flux,the detector area, on--source duty factor, relative v - Y

Em.rn S,(> Em.r.) 1 .5 _2_2.1 2 .53 x 10' 5 eV 1.5 x 10'' 4cm-2sec- ' .3 n,, = 3 49 94 2000 yr- ' Haverah Park2 x 1O' r' 7.4 x 10- ''' .3 10 160 300 5300 Kiel5 x 10 , 3 8.2 x 10-13 1 5 13 18 70 CYGNUS1X10' 4.6x10- l', .1 5 150 330 11,000 LMC X-43X10' 9x10- '' 1 .5 10 20 400 Vela X-1

42

intensity,

the amount of y ray attenuation, and spectral

index,

and can be resealed straightforwardly to different

values .3 .

Proton Luminosity Estimates

In

order to extend these estimates to other sources,

an

estimate of the total power in the source is required

.

This

can be evaluated for the case of Cygnus X-3

. Inits

quiescent state, Cyg X-3 has low-level radio flares

repeated

approximately every 4

.9

hrs

.

These events be-

have

like standard expanding synchrotron sources with

energy

ti 10

-11 ergs

and average energy output

2' Lk

-

10"ergs/4.9

hrs" 6 x 1036erg sec-'

.

(This is a lower limit

to

the total energy content, since this estimate refers only

to

the radio-emitting electrons with -y - 103

.)

In the case

of

the large 1972 radio flares, Seaquist29 has estimated a

total

emitted radio energy of 1044 ergs and an explosion

energy

in excess of 10" ergs, corresponding to 5 x 10'9

Mo

of relativistic particles moving outward at high ve-

locity.

Expansion velocities as high as iQ = 0

.3

have been

measured

in subsequent outbursts3u

.At

higher energies, Vladimirskii et alai' give the fol-

lowing

time-averaged luminosity values

:

These

values assume isotropic emission, and in the case of

the

highest energy value include allowance for a factor of

3

attenuation on the microwave background =

1/3)

over the 12 kpc path to the earth

.

Typically, the

maximum

luminosity of an accreting system is taken to

be

the Eddington luminosity, where the photon pressure

balances

the spherically symmetric accretion from the

companion

onto the neutron star

:

4xeGMmp

K

M

L1,;,1

= -

=

1

.3

x 103 -- erg sec-' ,

(11017 .

)Ah.

where

a-,

.

is the Thompson cross section and Af is the

mass

of the accreting companion

.

The observed x-ray

and

HE y ray fluxes from Cygnus X-3 are already close

to

the allowed limit

.

M.L .

Cherry/Cosmi

c

neutrino fluxes

In

the case of the UHE emission, Hillas4 has calcu-

lated

the luminosity of 1017 eV protons required to ex-

plain

the -i ray flux measured above 101$ eV at Haverah

Park .

The time-averaged flux of 3 x 10-'u ergs cm-2 sec-'

(after

accounting for the microwave losses in 12 kpc) is

measured

over only 2% of the orbital period

.

On the as-

sumption

that the protons are accelerated constantly into

a

solid angle of 11 sr, and that the low duty factor simply

reflects

the geometrical alignment of the target between

the

neutron star and the earth, then the 2% duty factor

implies

a factor of 50 fl/47r magnification in the proton

power.

Furthermore, only ti 10% of the 10" eV proton

power

is actually channeled into UHE y rays (since only

1/3

of the proton energy goes into the a° channel

;

some

of

this is at lower energies

;

and an additional component

is

carried away by nucleons escaping from the target re-

gion) .

The total power in 10'7 eV protons must then

beLprolons

^' 5 x 1039 St ergsec-1 > Led

.

(12)4aBrecher

and Chanmugam32 argue that in this case the p-

p

cross section should be substituted for or in Eq

.

(11),

so

that the maximum allowed proton luminosity becomes

LI:d,protons

^' 1041 erg sec-'

.

(13)

This

is consistent with observations of a radio jet requir-

ing

103`1 erg sec-' and with the observed period slow-

down

P ti 10-9, which implies a steady mass outflow of

10-'

- 10-s M() yr-' from the system and a correspond-

ing

accretion luminosity Laccrrléon ^' 10 "' - 101' erg sec-',

sufficient

to power the initial proton beam

.The

neutrino flux corresponding to this power esti-

mate

can be calculated from Eq

.

7 if we assume

.1

is

independent

of energy

.

We further use the Gaisser and

Stanev`

result that the calculated flux depends on the

total

proton luminosity but is insensitive to the exact

shape

of the spectrum (i

.e.,

they find nearly the same re-

sults

for a monoenergetic 1017 eV proton spectrum or an

E-2

power law)

.

The time-averaged Cygnus X-3 gamma

Lz(2 -

10 keV)

= 1 .4

x 10" erg sec-'

L,(> 40

MeV)

= 3

x 1033

L,,(> 2

TéV)

= 5

x 1036

L,(> 2

PeV)

= 1.1

x 1036

.

ray fluxes are

(2 f 0.6) x 10-1 '; cm-2sec- '

(Kiel)S.,(> 10 1 'eV) _

(4.5 - 7) x 10`

(Haverah Park)< 7.5 x 10- ' s(LosAlamos)

Scaling to the lower Haverah Park flux, and using Hillas'estimate of the proton luminosity and a distance of 12

kpc, the neutrino flux becomes

S�(> E)

=

2 .7ox

10-13CM-2sec-1

(10ëV

x

_J1 L,, 12kpc)2

20

5 x 1039erg sec-'

d

(14)

The upward-moving muon flux from Eq. 10 is then

EA lr(a)

(0.4 x6x10.1m2/x

_a

Lp

12kpc 2

20

5 x 1039erg sec-'

d

(15)

4 . Application to Specific Sourcesa. Binary Star Systems . Based on the observed ,y

ray emission, Hillas ' has estimated the power output of

the other UHE-emitting binaries:

Gaisser et a1. 2 ' have made similar estimates . Except for

Cyg X-3 (where they estimate Lp - 10''9 ), their esti-

mates agree with those of Hillas . Cygnus X-3 itself is

a Northern Hemisphere object, so that GRANDE and

DUMAND have only limited sensitivity (if any) in this

case . As discussed in Sec . 2, however, the binary x-ray

source LMC X-4 (e = 0.43 from the GRANDE site),

although extragalactic, appears to be a promising and

well-positioned candidate source likely to be as intense

as Cygnus X-3 .The recent detection of bursts of events from Her X-1

at both TeV" and PeV"` energies allows an estimate of

burst fluxes of high energy neutrinos from this or similar

sources . If the flux at TeV and PeV energies follows a

M.L. Cherry/Cosmic neutrino fluxes 43

power-law spectrum of differential spectral index about-2, then the gamma ray luminosity during the burst isabout 1038 ergs sec- ' above 100 TeV. Thus, during theburst the gamma ray luminosity is comparable to thesteady state proton flux given above. If these burstsare characteristic of all UHE-emitting x-ray binaries, itmakes the detection of high energy neutrino bursts fromsources such as Vela X-1 and LMC X-4 an intriguingpossibility . The possibility of detecting neutrinos fromtransient VHE and UHE ,y ray burst events is discussedin more detail in Sec. 5 .

SS433 (E = 0.21) is an x-ray and radio-emitting galac-tic binary with a relativistic jet structure similar to that

oflarge radio galaxies . Power estimates33 for SS433 rangefrom 3 x 1039 to 10" erg sec- '

kpcLp(erg sec- ')

d(kpc)

Lp x (1- 2 ) 2

SS 433

3 x 10395

2 x 10"10 -1 '

5

6 x 10-i1

If a reasonable fraction of the SS433 power output is

channeled into neutrinos, its intrinsic luminosity togetherwith its proximity .sake it an excellent possibility for de-tection .

b . Non-Stellar Sources . For non-stellar sources,

Shapiro3' estimates the electromagnetic power output of

the quasar 3C273, the radio galaxy Cen A, and the Seyfert

galaxies NGC1068 and NGC4151 to be :

Of these four, only Cen A has been detected above 1 TeV,

although its normalized power is smaller than the corre-

sponding values for the two Seyfert galaxies . Shapiro

points out, however, that the high energy ,y rays me sup-

pressed by pair production on the ambient x-ray field

(-y-y, --* e+e.-): the optical depth for a Seyfert galaxy

with radius 2 x 1013 cm and x-ray luminosity 10 -17' erg

L,(erg sec-') d(kpc) Lp x('2d )2

Her X-1 1038 5 6 x 1038Vela X-1 1037 1 .4 7 x 1038

Cyg X-3 5 x 10:1 `1 12 5 x 1039

LMC X-4 10" , 55 5 x 1039

L,,(erg sec-') d(kpc) 2LN x ( t?d~~3C 273 10'' 6 x 10!' 4 x 103'

Cen A LO 1'' 4 x 10'' 9 x 10'l'

NGC 1068 10" 1.5 x 10*1 6 x 1038

NGC 4151 10" 1.5 x 10' 6 x 10:'8

44

sec_' is 105 (E/1 GeV), where E is the -y ray energy. The

power levels above are then only lower limits . Shapiro

calculates that even though the UHE .y rays may there-

fore be unobservable from Seyfert galaxies, NGC 1068

(c = 0.24) may yield > 20 neutrino-induced muons yr-1

(0.24 x 6 x 10'' m2)' l with a nonthermal E-2.35 spectrum.

Similarly, Silberberg and Shapiro's estimates 35 , using a

model of a central black hole in the galactic core as the

Seyfert galaxy power source, give - 20 neutrino events

yr- ' above 4 TeV in a 0.2 x 6 x 10' m2 detector for a

typical Seyfert galaxy at a distance of 20 Mpc (i .e ., inthe Virgo Cluster) . The estimates depend strongly onthe particular assumptions of beam collimation, protonluminosity, and spectrum .

Intense, variable, superluminal radio sources, such asthe quasar 3C273, may also be observable in neutrinosby GRANDE. Scott36 has pointed out that if a typi-cal outburst from 3C273 is 1057 ergs and if one-half ofthe total energy results in neutrinos, then bursts of per-haps 105 neutrinos per cm2 lasting for about 105 sec-onds should occur . From Eq. 15, the expected numberof upward-going neutrinos observable in GRANDE maybe estimated . For a spectral index a = 2.1, 100 upwardgoing muons in 105 sec are expected . 5 There are sevensources known with redshifts less than 2, superluminalexpansion, and outbursts on the average of once everyfew years . The transient nature of these sources makesattempts to observe them with standard TeV Cerenkovdetectors and PeV shower arrays, which are typically lim-ited to zenith angles within 30° of the vertical, chancy.This is especially true for air Cerenkov detectors, whichare limited to a few clear dark nights every month . A neu-trino detector, on the other hand, is able to view a sourcewhenever the source is below the horizon, and thereforemay be more Nicely to detect such transient burst sources .

e . Young Pulsars . It is assumed that young pulsars4 1t is interesting to note that Volubiev et al ." have reported a

burst of 100 MeV photons from another superluminal radio source,3C120, with flux 5 x 10-a CM-2 sec- ' corresponding to a total en-ergy output in excess of 10 5' 3 ergs over 5 x 10 r' sec . Independentestimates of the energy output of bursts from 3CI20 give - 10r''1ergs.

M.L. Cherry/Cosmic neutrino fluxes

are efficient high energy cosmic ray accelerators . Mag-netic fields of 10' 2 gauss, millisecond rotation periods,

and the presence of ejected nebulae of target materialprovide the ingredients for both the primary accelera-tion and the production of gamma ray and neutrino sec-ondaries . The list of observed UHE and VHE gammaray sources seems to confirm this: with the exception ofthe radio galaxy Cen A, every VHE and UHE gammaray source so far detected is associated with a neutronstar. Although the rate of observed supernovae (bothin our own Galaxy and in external galaxies) is probablyno greater than 1 per 20 yrs, the pulsar birth rate ap-pears to be closer to 1 per 6 years : essentially every starwith a mass in excess of about 2 Mo appears to producea neutron star . Based on estimates of pulsar lifetimesand space densities, Helfand3s suggests that there maybe as many as 10' neutron stars in the Galaxy. Thiscorresponds to a distance to the nearest neutron star ofapproximately 10 pc . If 0.1% of these neutron stars arestill young enough to produce UHE emission, then therecould be as many as 10' interesting objects in the Galaxy.We can estimate the neutrino flux based on Ruderman'sestimate 39 of between 4 x 10'° and 1033 erg sec- ' for thepulsar's initial energy loss rate . Based on Eq . 15 andthe assumption of a power law spectrum with a = 2.1,a pulsar with a spin-down rate of 4 x 10" erg sec- ' ata distance of 12 kpc can then be expected to produce 60events month- ' in a detector the size of GRANDE. At1043 erg sec- ' and 1 Mpc, the rate drops to 2 month-' .A distance of 1 Mpc includes most of the mass of thelocal group (- and brings the expectedsupernova rate to fs.v - 2.4 x 0.05 yr - ' - 0.12 yr -' .

d . High Energy Supernova Neutrinos. The ob-servation by IMB "' and Kaniiokande" of a burst of lowenergy neutrinos frorn SN1987A confirmed many expec-taLions about the stellar collapse process . Although highenergy neutrinos have not yet been seen, one expects thatprotons will be accelerated to exceedingly high energiesin the supernova remnant . The acceleration mechanism

employed by a supernova to produce the high energy par-ticles seen in the cosmic rays is not known . Two mech-anisms which have been discussed are i) the shock waveacceleration due to the collapse expanding into the in-terstellar medium and ii) the direct acceleration due torapidly rotating magnetic fields . If the protons and/orions accelerated by such a mechanism collide with a gasshell of sufficient thickness left over from the progenitorenvelope, neutrinos can be produced at high energy. Theabsolute flux ofsuch neutrinos is characteristic of the par-ticular acceleration mechanism and its observation canbe a valuable diagnostic tool. Gaisser and Stanevl2 havepredicted that fluxes of upward-moving neutrino-inducedmuons might be present at a level of 90(Lp/1013 erg s-')month- ' in a detector of 6 x 104 m2 , where Lp is theproton luminosity. This estimate assumes a power-lawspectrum with a = 2.4 ; a harder spectrum or proton en-ergies much in excess of 1 TeV could produce as many as2000 muons month- ' in GRANDE.5 . Simultaneous Gamma Ray-Neutrino Observa-tions

It is instructive to compare the neutrino sensitivityto the gamma ray sensitivity of other detectors . As-suming a power law spectrum, we can express the in-tegral gamma ray intensity S.,(> E) corresponding tothe neutrino-induced muon rate n,, as

Sy(> E)E

),`100MeV

(3x107)`Y - ' n,, _20 0.4x6x101 m2

r(a)

20 yr-' a

eA

9 x 10- '3 cm-2sec- '

As a first example, we can compare this intensity tothe. point source sensitivity of the high energy gamma raydetector (EGRET) to be flown aboard NASA's Gamma .Ray Observatory''' . This will be a 1000 cm' spark cham-ber and Nal detector designed to cover the energy range

20 MeV to 30 GeV. Above 100 MeV, the point source

sensitivity will be 10'' cm--='sec-` or better with angula.rresolution of up to 0.1° and energy resolution of 150 . Forthe case a = 2, the 100 MeV -y ray intensity correspond-

M.L. Cherry/Cosmic neutrino fluxes

ing to a rate of 20 yr- ' in GRANDE is

S,(> 100MeV)

=

5 x 10-7CM-2sec- ' xn,,20 0.4 x 6 x 104M2

20 yr- ' a

eA

S,(> MV) = 5 x 10-" cm-2sec- ' xn,, 200.4x6x10'mt

45

This level corresponds favorably to the SAS II and COSB sensitivities (The weakest of the 25 sources in the COSB catalog of Swanenburg et al." is at 6 x10` 7 cm-2sec-1),and should permit correlated neutrino-gamma ray obser-vations .

In the VHE range, Eq. (16) gives

120 yr- ' a

eA

For comparison, consider Weekes' catalog3 of VHE -r

ray sources . PSR 1801-23, Cyg X-3, Her X-1, and 4U

0115-}-63 have all been reported at levels of 3 x 10-"cm-2

sec- ' or higher . For Southern Hemisphere sources, thePotchefstroom (South Africa), White Cliffs (Australia)

and Narrabri (Australia) Cerenkov detectors will allowcorrelations at this level.

Finally, at UHE energies,

S,(> 1PeV)

=

5 x 10-'1 CM-2sec-'fR-wane xn,, _20 0.4x6x10-1 M2

20 yr- ' A

eA

'

a level at which the Adelaide and Buckland Park (Aus-

tralia), JANZOS (New Zealand), and SPASE (South Pole)

air shower arrays can also work .

It is instructive to turn this argument around, and

ask what neutrino-induced muon rate corresponds to the

7 ray bursts apparently observed from Her X-1 by the

CYGNUS experiment . At energies above approximately

100 TeV, Dingus et al .'t have reported two 30-minute

bursts of 7 events and 12 events on July 24, 1986 . They

suggest a flux S7(> 100TeV) - 2 x 10-" cm-'sec- I .

Neglecting any attenuation of the photons, and assuming

A =- 20 and a differential spectral index ct - 2, Eq. 16

gives a corresponding muon rate of 1 per 11 hours in

0.4 x 6 x 10' m1 ; for a - 2.5, the neutrino-induced inuon

rate becomes 1 per 100 minutes .

46

I gratefully acknowledge numerous helpful discussions

with many of my colleagues in the GRANDE collabora-tion .

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