A knowledge of the flux of antiprotons is of value in examining the manner in which cosmic rays propagate, assuming, as is conventional, that the antiprotons arise from interactions in the I.S.M. Golden et al. (1979) have recently measured the ratio in the region of 10 GeV and, although confirmatory measurements are needed, it is instructive to compare with expectation. In a recent paper (Szabelski et al., 1980) we presented results of a new calculation of the expected ratio using the standard (equilibrium) ‘leaky box model’.

Today X-ray astronomy encompasses almost all astronomical objects, from nearby stars to the most distant quasars. We review a few selected recent results obtained by X-ray astronomy on galactic objects like normal stars, supernova remnants, neutron stars and the black hole candidate Cyg X-1.

Recent observations by the Einstein Observatory have shown that a majority of known quasars are powerful X-ray emitters. The 107 objects observed as of Feb. 1980 (Zamorani et al. 1980) have X-ray, optical and radio luminosities scattered over a wide range. Until a large enough X-ray selected sample of quasars becomes available, it is necessary to study statistical correlations in the available sample, so that some insight into X-ray production may be obtained, and the contribution of quasars to the X-ray background estimated.

Assuming that the gas in the halo of a disk galaxy is supplied from the disk as a hot gas, we have studied its dynamical and thermal behaviour by means of a time dependent, two-dimensional hydrodynamic code.

Recent experimental results (Giacconi et al, 79, Tananbaum et al 79) ascribe an increasingly important role to the contribution of discrete sources to the low-energy (few Kev) cosmic X-ray background (CXB). While the astrophysical nature of the objects involved is not yet clear, distant and powerful emitters like QSO play probably an important role (e.g. Setti and Woltjer 1979, Field 1980). For them, often the number-flux curve (LogN-LogS) provides useful hints on such properties as space distribution and/or evolution. For the case of the X-ray sources, moreover, a definite relation exists between their LogN-LogS and the granularity of the sky emission as described by the fluctuations of the X-ray background.

When we talk of Gamma-Ray Astronomy we refer in general to celestial photons covering the energy domain from a fraction of MeV up to the highest detected energies at hundreds or thousands of GeV. The six to seven decades altogether spanning the overall energy range constitute a very wide domain to be compared with those of the optical (less than one decade) or of the neighbouring X-Ray Astronomy (about two decades). The observational technique varies widely with changing energy; detector performances and characteristic parameters are not, in general, comparable.

It is shown that there is evidence favouring molecular clouds being sources of γ-rays, the fluxes being consistent with expectation for ambient cosmic rays interacting with the gas in the clouds for the clouds considered. An estimate is made of the fraction of the apparently diffuse γ-ray flux which comes from cosmic ray interactions in the I.S.M. as distinct from unresolved discrete sources. Finally, an examination is made of the possibility of gradients of cosmic ray intensity in the Galaxy.

Within the error circle of the COS-B gamma-ray source at ℓ = 288°, b = 0° lies the Carina Nebula, one of the most active regions of star formation known, housing several OB associations and Wolf-Rayet stars (WRS), and perhaps also a supernova remnant (SNR). As a region containing intense mass-losing stars it belongs to the same species as the Rho Oph cloud (but much more active), suggested to be associated with the gamma-ray source at ℓ = 353°, b = +16° (Paul et al., this conference). As a group of OB association linked with a SNR, it belongs to the same species as “SNOB's” (Montmerle, 1979), possibly identified with about half of the COS-B sources. We suggest that the source at ℓ = 288°, b = 0° should be identified with the Carina complex. In this case the source would be at ≃ 2.7 kpc and its gamma-ray luminosity would be ≃ 2.1035 erg s−1. It is suggestive that the nearest aggregate of stars, gas and dust (Rho Oph) and the richest one (Carina) are both in the direction of a gamma-ray source. The Carina complex is noted in particular for the compact star clusters Tr 14, Tr 16 and Cr 228 (Humphreys, 1978), altogether comprising 6 of the 7 O3 stars observed in the Galaxy. It is also remarkable that 3 WRS are associated with the complex. All 3 WRS are of the WN7 type, having the highest mass-loss rate of WRS (≃ 10−4 M⊙ yr−1). Even more remarkable is the presence of the strange Carina object which sheds mass at the extraordinary rate of 10−3 to 0.075 M⊙ yr−1, with a velocity of ≃ 600 km s−1. Moreover, according to radio (Jones, 1973) and optical (Elliot, 1979) data, there seems to be a SNR buried in the Nebula. However, it is not seen at X-ray wavelengths by the Einstein observatory (Seward et al., 1979). This could be explained if the SNR has a luminosity Lx < 1034 erg s−1, since it could then be conceivably hidden by the unstructured, diffuse X-background. The molecular cloud associated with the Carina Nebula has been observed in the lines of H2CO and OH (Dickel, 1974). The cloud has a derived mass of ≲ 105 M⊙, typical of other molecular clouds.

Supersonic stellar winds have recently been proposed as active agents of cosmic-ray acceleration. We try to insert this potential acceleration mechanism in its general astrophysical context. Among galactic objects, OB associations have the narrowest latitude distribution, resembling to that of gamma-ray sources. Here we focus on the bulk rate of kinetic energy deposition in molecular clouds through stellar winds of individual stars pertaining to OB associations. Assuming that a minute fraction of this mechanical energy can be transferred to suprathermal particles, we examine whether OB associations are detectable high-energy gamma-ray sources, owing to the interaction of accelerated particles with the dense molecular cloud still present close to young and massive stars. The 3 factors that govern the gamma-ray “visibility” of a given OB association are i) the rate of kinetic energy deposition , where the summation is done on all mass-losing stars; is the mass-loss rate for the star i and Vi is the terminal velocity of its stellar wind;(ii) the distance of the OB association;(iii) the angular extent of the association.

It has long been expected that gamma-ray astronomy will visualize the mysterious cosmic-ray (CR) sources. Indeed, on the basis of COS-B observations, it has been proposed that CR acceleration within the Rho Oph cloud complex (ROCC) is required to account for its gamma-ray luminosity (Cassé and Paul, 1980, herein after CP, Bignami and Morfill, 1980). However, Issa et al. (1980) have suggested that the size of the ROCC has been underestimated by a factor ≃2, and that the cloud mass is a factor ≃ 4 higher than given by Myers et al. (1978), making unnecessary CR acceleration and trapping in the cloud interior.

A search has been made for very high energy photons from the direction of the Crab Pulsar using the Lodz extensive air shower array. This device is particularly suitable for such a study because it consists of a large muon detector which can be used to search for the characteristic muon poor showers.

One of the most recently detected (Cline et al., 1980) Gamma Ray Bursts (GRB) appears to have very unusual properties.

We recall here briefly the main features of the time history and of the spectral data, as given by Cline (19 79). The time history has a very fast initial rise, less than 200 usee , a smooth, large but very short initial peak, with a maximum intensity of several × 10−3 ergs cm−2 sec−1 and a 150 msec duration, followed by an oscillating decay phase, with at least 22 compound 8 second pulses. The spectrum of the initial phase of the event; corresponds to a steep power law with possibly a line at 420 keV. The total spectrum of the decay phase is even steeper and shows no lines (Mazets and Golenetskii, 1979), The location of the wait (Evans et al., 1980) corresponds to N49, a supernova remnant in the Large Magellanic Cloud, which gives a total (isotropic) emission of ≈ 1045 erg, one half of it in the initial spike, the rest in the decay phase. Three later events, apparently with no special properties, are attributed to the same source (Mazets and Golenetskii, 1979), with increasing delays (0.6, 29 and 50 days) and decreasing peak intensities (3%, 1% and 0.5% of the first event), because their locations are all consistent with the much smaller March 5 error box.

The galactic luminosity for 0.1 < Eγ < 2 GeV can be evaluated directly from observational data and the commonly accepted value is 5 1038 erg s−1. Various contributions to the γ-ray emission can be recognized, namely i) strong sources, ii) pulsars, and iii) diffuse processes. Their relative importance is discussed in the following.

In our recent work we have shown that a good model for the highest energy cosmic rays is one where they are generated in clusters of galaxies with a relatively flat production spectrum and then propagate with an energy dependent diffusion coefficient. There is evidence for a similar flat production spectrum (γ ≃ 2.1) for both protons and electrons in our own Galaxy. Here we assume that the spectrum for clusters (specifically the VIRGO cluster) is independent of energy and an evaluation is made of the likely flux of γ-rays.

In the case of spherical symmetric accretion into a black hole, the matter may be heated up to the temperature KT = 0.1 mpc2 (Kolykhalov and Sunyaev, 1979). In such a hot plasma inelastic collisions of protons may produce Π° which is the gamma quantum source.

In this work we determined γ-rays production spectrum in the comoving plasma reference frame, expected γ-rays spectrum for the case of spherica symmetric accretion of matter into a black hole and the upper limit to the number of black holes in Galaxy is evaluated.

The publication of the first and preliminary second catalogue of the COS-B sources, has brought to the attention of the astronomical community the new reality of the high-energy Galactic Gamma-Ray Sources (GGRS). It is worth recalling here the definition of such objects, in the COS-B sense: “A GRS is a significant excess of photon counts, compatible with the instrument's angular resolution, or, more clearly, with the instrument's Point Spread Function”. This definition of an unresolved (as it is the case for the vast majority of the GGRS) GRS is, to some extent, dependent on the shape of the source spectrum; however a general shape of the PSF for the case of the source associated with 3C273 can be found in Bignami et al, 1980. Naturally, the absolute flux (i.e. the total number of photons) from a source is also important in determining the positional error, especially when usage is made of the cross-correlation method. Typical photon numbers (100 Mev) for GGRS range from 50 to few hundreds. The COS-B catalogue error boxes are defined taking into account both the PSF and the photon statistics; it is then apparent that the search for candidate counterparts of the GGRS should be carried out inside such boxes, or in their immediate vicinity, and that, for examples, such loose positional coincidences as obtainable by increasing a quoted error radius by 50%, let alone doubling it, are totally unacceptable. Systematic searches for counterparts at other wavelengths have not yet been carried out, except for a few cases of X-ray and radio observations, as for example in the case of CG 135+1 (the only COS-B GRS erbox compatible with a 4U erbox) which led to the discovery of a new X-ray QSO by Apparao et al, 1978.

Although it is clear that cosmic rays are of considerable astrophysical significance we know surprisingly little about their origin(s), their mode(s) of propagation and escape from the galaxy, and even of their general properties. Practically nothing is known of the composition and energy spectra of different species at energies below about 200 MeV/nucleon as a consequence of solar modulation, which has a significant effect on the observed spectra at energies up to about 10 GeV/ nucleon. The energy spectra of ions (especially protons) appear to be well approximated by a power law (differential spectral index γ ~ 2.6) in the range 1010–1015 eV/nucleon. At higher energies (up to ~ 1020 eV/nucleon) both the spectrum and the composition of the ion component are less well known, however it is significant that the anisotropy, as evidenced from the sidereal diurnal variation, increases substantially, suggesting that perhaps an extragalactic origin must be considered.

Diffusive Fermi acceleration on hydromagnetic shock fronts is a fairly slow process: most scatterings are energetically neutral, only those across the velocity jump yield a first order acceleration. Thus energy losses of cosmic rays (CR) due to e.g. adiabatic cooling, ionising, Coulomb−, or nuclear collisions, bremsstrahlung, synchrotron radiation, should play a role in limiting the acceleration, since most shocks are coupled with a loss region (HII regions, SNR's, galactic density wave, stellar wind shocks). In addition, for this process to be a local one in the galaxy, the magnetic irregularities must either be excited by the accelerated CR's or produced by a downstream source. This implies a finite wave build-up time during the shock life time. Nevertheless, in the loss free case, the time-asymptotic amplification is independent of the mean free path λ (or the diffusion coefficient κ) which only appears in the spatial scale for the CR intensity. To investigate the effects of losses, the CR diffusion equation is amended by a simple loss term f/τ, with an (energy dependent) loss time τ, f being the CR momentum distribution. For τ spatially homogeneous, a distributed source is required. Then acceleration is only effective if X ≡ 4κ/VS2·τ ≲ 1, i.e. if the acceleration time tacc = 4κ/VS2 is smaller than τ, on either side of the shock. As the Figure shows, also the spatial intensity profile is modified. Wave excitation in dense clouds is prohibitive. Even in a “warm” (T ≃ 104K) intercloud medium shock speeds VS ≳ 3×107 cm/sec are required to accelerate mildly relativistic particles. Waves from an upstream source (star) inside clouds should frictionally dissipate after distances L ≲ 5×1014 cm « λ (10 MeV) if a solar wind scaling is adopted. Thus, presumably in such a case there is no acceleration of stellar or shock-injected particles through a stellar wind shock by scattering within the cloud, but possibly by reflection from beyond the cloud, the condition being 1/τ · VS ≲ 1, where 1 is the linear cloud size. Diffusive approach from outside to a standing shock appears to be very energy-selective, even in a loss free medium.

When corrected for the effects of propagation in the interstellar medium (i.s.m.), the observed composition of galactic cosmic rays can give us some clues as to the origin of these particles. It is noteworthy that the main pecularities of the cosmic ray source composition (CRS), as compared to normal i.s.m. abundances, bear some resemblance to that of i.s. grains, as inferred from i.s. absorption line measurements (e.g. York 1976): (1) the refractory elements Al, Si, Mg, Ni, Fe and Ca, which in i.s. clouds are almost completely locked into grains, are present with normal abundance ratios in the CRS. (2) normalized to Si, the volatile and reactive elements C, N, O, S and Zn are underabundant in CRS by factors of 2.5 to 6; these elements are only partially depleted in the i.s.m. (3) at a given rigidity the ratios H/Si and He/Si are lower than in the i.s.m. by a factor of ~ 25; while H and He atoms are virtually absent in i.s. grains. (1) implies that cosmic rays originate in astrophysical sites where the grains have either not condensated as yet, or where they have been (at least partially) destroyed. Then, to account for (2) and (3), one might consider that an unspecified mechanism selects the particles to be accelerated, possibly according to their first ionization potential (Cassé 1979 and references there-in).

The backreaction of shock accelerated cosmic rays (CR) on the hydrodynamic flow is studied in a simple macroscopic modeL introduced by Axford et al. (1977): the fluid is isentropic except at discontinuities and the energy of the scattering wave field is neglected. With gas density p , velocity u, pressure pQ and a constant specific heat ratio γQ we have in the one dimensional steady state: