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Discussion of the soft X-rays from Virgo observed with a scanning focusing collector from an Aerobee 170 rocket. The region included the center of the Virgo cluster of galaxies, a source of higher energies which had been previously identified with M87, and QSO 3C 273. No discrete sources in Virgo were observed.
Results are presented of the analysis of data from observations of extragalactic objects with the imaging proportional counter on board the Einstein Observatory. Surveys of normal galaxies, radio galaxies, active galaxies, quasars and BL Lacs, and clusters of galaxies were studied in order to improve the understanding of the origin of the Milky Way Galaxy.
Four weak sources for which precise positions have been obtained from the HEAO-1 Scanning Modulation Collimator (MC) experiment are discussed. One source (4U 0446+44) with the center of the cluster of galaxies containing 3C129 and 3C129.1 has been identified, and its angular size has been measured. One source with a galactic star is identified, although it is at galactic latitude b = 51 deg. The other two sources, 2A 0526-328 and 2A 0922-317, remain unidentified.
Recently reported observations of the 3-K microwave background in the direction of rich clusters of galaxies should be viewed as placing stringent limits on the mass of cooler ionized gas within the clusters, rather than as a verification of thermal bremsstrahlung models for cluster X-ray sources. At the high radio frequencies employed in the observations, there is a positive contribution to the observed source-brightness distributions from free-free emission by any cooler gas. This can overwhelm the anticipated inverse Compton diminution of the background radiation, even when the total mass in cooler gas is significantly less than the mass of hot plasma required to explain the X-ray source. Future experiments of this type should be conducted only when atmospheric stability is sufficient to permit lengthy drift scans across the clusters. Extreme care must be taken to remove the contributions from any discrete sources.
Results obtained from the Focal Plane Crystal Spectrometer (FPCS) are presented with particular reference to supernova remnants Puppis A and Cas A in the Galaxy, and N132D and N63A in the Large Magellanic Cloud. A schematic diagram of the FPCS is given, and spectrum reconstruction is outlined, noting that the final spectrum consists of a histogram of counting rate vs. energy corrected for the exposure time in each energy bin. Consideration is also given to the Virgo cluster and its two X-ray components: the hot exponent extending throughout much of the cluster and a cooler, 'halo', component centered on M87. FPCS observations of central M87 are presented, and it is postulated that the central portion of the M87 'halo' source contains material with a dominant temperature near 10 to the 7th K or below about 2 x 10 to the 6th K.
The HEAO 1 modulation-collimator data associate the X-ray emission from the Cygnus A region (4U 1957 + 40) with a small area including the radio galaxy. The source appears to be extended, with a size of about 2 arcmin; it may have a complex geometry. Any point-source component must have a flux no greater than 1.3 UFU. A lower limit of 1 microgauss is placed on the magnetic field in the radio lobes, based on the upper limit on the X-ray flux due to inverse Compton scattering of radio electrons on the 2.7-K microwave background radiation. The X-ray emission is more likely due to driven accretion of the intercluster gas onto the giant cD radio galaxy. Therefore this source appears to be similar to the Virgo and Perseus clusters. The density derived for the X-ray-emitting gas is too small for its thermal pressure to confine the radio source.
The HEAO A-2 all sky data base was surveyed for 2-10KeV X-rau emission from the 225 Abell clusters og galaxies listed in Abell's (1958) catalog which are of distance class four or less, and are within the fraction of the sky surveyed completely by Abell. Thirty-two identifications of clusters with X-ray sources were made, for which 2-10 KeV fluxes and 90% error boxes are presented. Twelve of these identification are new. The X-ray luminosity function was derived for this statistically complete sample and the best exponential fit was found to be f(L) = 20.2 x 10 to the minus 8 power exp (-l(44)/1.9) per cu Mpc 2-10KeV. The relationship between X-ray luminosity and richness was examined and a correlation was found for richness classes 0, 1, and 2. The relationship of X-rau luminosity, Bautz-Morgan type, and Rood-Sastry type was examined. It was found that BM type I's and RS type cD and B have the greatest average luminosity. The contribution of clusters to the X-ray background was calculated from the luminosity function and was found to be 5%, and with 90% certainty, less than 8% in the 2-10 KeV band pass.
VLA radio maps and optical identifications of a sample of sources in the directions of 21 Yerkes poor cluster fields are presented. The majority of the cluster radio sources are associated with the dominant D or cD galaxies (approximately 70 percent). Our analysis of dominant galaxies in rich and poor clusters indicates that these giant galaxies are much more often radio emitters (approximately 25 percent of cD's are radio active in the poor clusters), have steeper radio spectra, and have simpler radio morphologies (i.e., double or other linear structure) than other less bright ellipticals. A strong continuum of radio properties in cD galaxies is seen from rich to poor clusters. It is speculated that the location of these dominant galaxies at the cluster centers (i.e., at the bottom of a deep, isolated gravitational potential well) is the crucial factor in explaining their multifrequency activity. Galaxy cannibalism and gas infall models as fueling mechanisms for the observed radio and X-ray emission are discussed
An analysis of the NRL HEAO 1 observations of the Virgo cluster and 3C 273 has revealed X-ray emission from a region between these two objects. The most satisfactory explanation is the presence of two weak X-ray sources, for which error boxes have been obtained. One source is likely to be the peculiar galaxy IC 3576, suggested by Margon et al. (1972) as the source 2U 1231+07=4U 1232+07. The error box resulting from combining the present observations with the 4U data strengthen the X-ray identification with this extremely interesting galaxy. There are numerous possibilities for the other X-ray source, including the interacting pair of galaxies NGC 4410a and NGC 4410b (NGC 4410a/b).
Recent observational and theoretical work presented at the Tenth Texas Symposium on Relativistic Astrophysics held in Baltimore, Maryland from December 15-19, 1980, is outlined. Areas covered include the theoretical foundations of relativistic astrophysics in general relativity, quantum gravitational theory and the association of grand unification with astronomical and cosmological issues, the cosmic microwave, X-ray, gamma-ray, UV, cosmic ray and gravitational wave backgrounds, the current expansion rate and average mass-energy density of the universe, and mechanisms of galaxy formation. Also discussed are the characteristics of active galaxies and clusters emitting in the gamma-ray and X-ray regions, and compact objects formed from supernova explosions, including pulsars, X-ray-emitting neutron stars, Sco X-1 and SS 433, gamma-ray sources, and X-ray and gamma-ray bursters.
The Coma cluster has been scanned by an array of large X-ray proportional counters equipped with 10 min x 4 deg (FWHM) collimators. The results suggest the peak surface brightness is not coincident with one of the two giant elliptical galaxies, NGC 4889 and 4874, and show the X-ray emission to be more extended in the 0.5-1.5-keV band than in the 1.5-5-keV band. No evidence is found for concentrated X-ray sources, like those in M87 and NGC 1275. The X-ray surface brightness contours have an ellipticity which resembles that of the galaxy mass distribution, and evidence is found for clumpiness in the intracluster gas.
The X-ray emission is interpreted from the fast-moving elliptical galaxy M86 (Forman et al. 1979) as evidence for the accumulation of an extensive gaseous envelope. The gas within this envelope is relatively hot, yet has until now been confined to the galaxy by the thermal pressure of the outer atmosphere of the Virgo cluster. The ram pressure of the intracluster gas in the cluster core is now stripping this envelope away. It is suggested that significant quantities of hot gas may be found in many elliptical galaxies.
A nonuniform model for a dense intergalactic medium is constructed under the assumption that all groups and clusters of galaxies are gravitationally bound by ionized gas. Catalogs by de Vaucouleurs and Abell are utilized to provide an almost complete sample of the spatial distribution of groups and clusters over a wide range of richness, and a distribution function is derived for galaxy groups and clusters as a function of velocity dispersion. A simple scaling law is applied to predict velocity dispersions for the very rich Abell clusters. Thermal bremsstrahlung emission from the intracluster gas accounts for the observed emission over 2 to 10 keV from several rich clusters, and also contributes up to 20% of the diffuse X-ray background over a considerable fraction of the observed range. The amount of X-ray emitting gas is restricted to a small fraction of the virial mass, with the remainder of the binding mass present as cooler ionized clouds. Available soft X-ray and ultraviolet diffuse background observations are used to define a narrow range of permissible temperatures and densities for these clouds.
Extragalactic cosmic X ray sources at high galactic latitude from sounding rocket experiments, correlating with galactic clusters
Diffuse cosmic X rays small scale structure, comparing Wolfe-Burbridge theoretical autocorrelation functions for galaxies clusters and superclusters with experimental value
A detailed analysis is given of the possibility that a large part of the primary cosmic-ray flux is of extragalactic origin. The problems encountered in theories of galactic cosmic rays are first critically discussed. The objections that have previously been raised to extragalactic theories, particularly on energetic grounds, are then examined. The general problem of the propagation of cosmic rays which are ejected from galactic nuclei or in galactic winds to fill clusters and superclusters is dealt with next. Attention is also given to the limits which are set on the presence of extragalactic cosmic rays by observations of high-energy electrons and background X-rays and gamma rays, or the heating of a hypothetical intergalactic gas. Observable effects of cosmic rays between galaxies are studied, and the possible sources of the local cosmic-ray protons in the extragalactic model are considered.
It is shown that the X-ray source in Virgo must be intimately associated with the galaxy M87, as evidenced by the coincidence of the source centroid location with the galaxy. Although the presented results do not completely explain the origin of the X rays from the Virgo cluster, they do indicate that the bulk of the emission does not come from the nucleus or the jet, and they also indicate the presence of strong energy processes in a region surrounding M87. One view of the origin of these X rays is that they are due to relativistic electrons ejected from M87, and interacting with magnetic or radiation fields in intergalactic space by the synchrotron of inverse Compton process. The other view holds that the X rays could be due to thermal emission from a hot plasma.
The elementary spectral signatures of fundamental physical processes that might be operable in galactic and extragalactic X-ray sources are reviewed. Some of the instrument limitations of experimental techniques used in X-ray astronomical spectroscopy are described. X-ray spectroscopic measurements are examined for various types of X-ray-emitting objects, including degenerate and nondegenerate stellar systems, supernova remnants, clusters of galaxies, active galactic nuclei, and quasars.