Search

This paper describes the calibration of the two solid-state Si(Li) X-ray detectors and the X-ray telescopes that flew as part of Goddard Space Flight Center's Broad Band X-Ray Telescope (BBXRT) experiment on board the space shuttle Columbia in 1990 December. During the 9 day shuttle mission, BBXRT performed approximately 150 observations of 82 celestial sources. The content of the archive is summarized here. Although BBXRT had a relatively short life, it stands as a milestone in X-ray astronomy as being the first instrument to offer moderate spectral resolution over a wide bandpass (0.3-12.0 keV). Among other things, this paper discusses the effective area calibration of the instrument, the flux calibration and flux corrections for off-axis observations, the detector background, and optimal background subtraction techniques. The on-axis effective area calibration for the central detector elements was performed using data from the Crab Nebula, while other carefully selected targets were used for calibration of the outer detector elements. The remaining systematic uncertainties in the effective area calibration for point sources observed both on and off axis are generally less than 5%-10%. The energy scale is known to better than 0.5% at 6.0 keV for both detectors. The results presented here have an impact on the calibration of other medium resolution X-ray experiments such as the CCDs on board ASCA (Astro-D) as well as the Advanced X-Ray Astrophysics Facility detectors.

We present the spectrum of the black hole candidate LMC X-1 as observed by the Broad-Band X-ray Telescope (BBXRT). The spectrum cannot be fitted by a simple model, but it requires a soft disk blackbody component and a power-law tail, confirming earlier studies. The blackbody disk component is essentially unchanged since the Ginga measurement in 1987. The implied mass of the compact object is approximately 4.7 (square root of cosine i) solar mass from the soft component fit. We report a 95% confidence detection of weak emission features at approximately 5.1 keV and approximately 7.3 keV. If the 5.1 keV feature is attributed to Fe I K-alpha at 6.39 keV, then the redshift is approximately 0.19. No quasi-periodic behavior is found in the data at this epoch.

The first moderate-resolution (FWHM∼160 eV) X-ray spectrum of a galactic black hole candidate in the 1-11 keV band has been obtained with the BBXRT experiment aboard Astro 1. There is a broad excess of flux in the 6-7 keV band above a simple power-law continuum which is consistent with that expected from reflection of the observed continuum from a disk of neutral material surrounding the central source. The edge at 7.1 keV due to photoelectric absorption by neutral Fe is deeper than that predicted for material of solar abundances, which suggests an overabundance of Fe in the source. There is little evidence for any emission features due to Fe with the possible exception of a narrow line at 6.4 keV with an equivalent width of 13±11 eV

We present the results of an observation of the high-luminosity quasar H 1821+643 with the Broad-Band X-Ray Telescope (BBXRT) performed in 1990 December. The 2-10 keV flux and power-law spectral index are found to be consistent with previous values obtained by EXOSAT and Ginga which indicates that the medium-energy continuum has remained steady for at least ∼6.5 yr. Contrasting with this is the result that the Fe Kα line present in Ginga observations of this source (observed equivalent width 210±80 eV) is not detected by BBXRT. We estimate that a narrow iron line, if it had been present during the BBXRT observation at the same strength as it was in the Ginga observations, should have been detected with a probability of 88%

We report on the results of a 2000 s observation of the nearby spiral galaxy M81 using the Broad-Band X-Ray Telescope (BBXRT). The observed X-ray emission is dominated by the flux from the nucleus, classified optically as a low-ionization nuclear emission-line region (LINER) (Filippenko & Sargent 1988). The 0.5-10 keV spectrum is well fit by a simple power law of photon index 2.20 (+0.3, -0.15), distinct from the flatter index observed in Seyfert galaxies. An upper limit of 90 eV has been placed on the equivalent width of any Fe K fluorescent feature. Taken together with the nondetection in the optical and UV of any nonthermal continuum emission, this argues strongly for the absence of an accretion disk around the M81 nucleus

The cluster of galaxies A2256 was observed with BBXRT (Broad Band X-ray Telescope) during the Astro 1 mission with a total exposure of ∼4000 s. Moderate resolution spectra of parts of this cluster of galaxies give information complementary to the high spatial resolution observation of the same cluster by ROSAT. ROSAT spectral images (Briel et al.) have shown evidence of a merger with the northwest clump being cooler than the main cluster body. The BBXRT spectra also show an indication of a lower temperature [kT=4.6(+0.9, −0.7) keV, 90% confidence errors] in the same general area

Cyg X-3 is well-known to be the brightest source of 6.7 keV iron K-line photons in the X-ray sky; this line has been unambiguously detected in data from OSO 8, Ariel 5, HEAO 1 A-2, the EXOSAT GSPC, Tenma, and Ginga, with measured physical widths (FWHM) ranging from 0.6 to 1.0 keV and equivalent widths typically from 0.5 to 1.7 keV. However, when the Shuttle-borne X-ray telescope BBXRT observed this source on 1990 December 5, the line was not detected. The BBXRT data show Cyg X-3 to be in an unusually high, soft state, with a luminosity of ∼2×10 38 ergs s -1 (1-10 keV; at 10 kpc), above the Eddington limit

The Broad-Band X-Ray Telescope obtained moderate-resolution (about 90 eV) X-ray spectra of the O4 f star Xi Pup during the STS 35/Astro 1 mission in 1990 December. Despite the shortness of the observation (600 s), the data show a surprising amount of detail. We report the detection of an O absorption edge produced by ionized overlying wind material and K-shell line emission from Mg produced by a thermal plasma of temperature near 6 x 10 exp 6 K. The data are used to place constraints on the location, temperature, and amount of the X-ray-emitting gas, as well as the abundance and ionization of the wind material.

We present our analysis and interpretation of spatially resolved X-ray spectroscopy of the elliptical galaxies NGC 1399 and NGC 4472 obtained with the Broad Band X-Ray Telescope. The X-ray emission from both galaxies is dominated by thermal emission from a hot interstellar medium. The temperature of the plasma in NGC 1399 is 1.0-1.2 keV with a mild positive temperature gradient; for NGC 4472 the average temperature is 0.7-1.0 keV. The temperature of NGC 1399, when combined with other X-ray and optical data, implies that, if the gas is gravitationally confined, about 70 percent of the mass inside a radius of about 8.6 arcmin (38 kpc) is nonluminous. The derived metallicities and metallicity gradients are consistent with optically determined stellar metallicities, and allow surprisingly small upper limits to be placed on Type Ia supernovae rates in both galaxies. The implications of this for the gasdynamical evolution of the two galaxies are discussed. Limits on the oxygen-to-iron ratio and the line-of-sight column density are derived. There is a possible detection of cold gas in the line of sight to NGC 1399 that exceeds the Galactic value. Constraints on the contribution from a harder spectral component are placed, and likely candidates for the origin of this secondary component are evaluated.

We report on BBXRT observations of the cataclysmic variable H0538 + 608 (BY Cam). The unexcelled energy resolution of BBXRT in the vicinity of the iron K line allows the line strength and energy to be constrained more tightly than has previously been possible. We are able to rule out a significant contribution from fluorescence on iron more neutral than Fe XVIII. Implications for the conditions in the accreting gas are discussed.

The Astro-1 Space Shuttle payload's Broad Band X-ray telescope has been used to obtain high-quality, moderate-resolution spectroscopy of Cygnus X-2 which allow the resolving of the physical width of the 6.7 keV Fe K-alpha feature with a factor-of-4 energy resolution improvement over past experiments. Three possible sites are noted for the Fe K-alpha emission: the accretion disk, its corona, and the source itself. It is judged that reflection from the accretion disk can generate a line of the observed energy, width, and equivalent width, provided that the disk surface is highly ionized.

We present new X-ray observations of Mrk 335 in the 0.4-10 keV band using BBXRT and in the 2-20 keV band with Ginga. The BBXRT data show a break to a softer spectrum below about 1 keV. The Ginga data show evidence for variability in absorption, uncorrelated with flux changes of the continuum source. The inconsistency between the opacity observed at the iron K edge and at softer X-ray energies implies that the absorber has an ionization state about FeXV. We suggest that the nuclear emission can be explained by a self-consistent pair cascade model as developed by Zdziarski et al. (1990) and Zdziarski and Coppi (1991), where the compactness parameter inferred from the spectral fits to both data sets is in good agreement with the value calculated from the ratio of observed X-ray luminosity and variability time scale.

A new X-ray observation of NGC 1068, in which improved spectral resolution (R is approximately equal to 40) and broad energy range provide important new constraints on models for this galaxy, is reported. The observed X-ray continuum of NGC 1068 from 0.3 to 10 keV is well fitted as the sum of two power-law spectra with no evidence for absorption intrinsic to the source. Strong Fe K emission lines with a total equivalent width of 2700 eV were detected due to iron less ionized than Fe XX and to iron more ionized than Fe XXIII. No evidence was seen for lines due to the recombination of highly ionized oxygen with an upper limit for the O Ly-alpha emission line of 40 eV. The discovery of multiple Fe K and Fe L emission lines indicates a broad range of ionization states for this gas. The X-ray emission from the two components is modeled for various geometries using a photoionization code that calculates the temperature and ionization state of the gas. Typical model parameters are a total Compton depth of a few percent, an inner boundary of the hot component of about 1 pc, and an inner boundary of the warm component of about 20 pc.

The Fe K-alpha emission line is a potentially powerful diagnostic tool in the X-ray spectra of AGNs, however, this feature has previously been observed with relatively poor spectral resolution. The Broad Band X-Ray Telescope has provided us with the first high-quality, medium-resolution X-ray spectral data. We are able to constrain the width of the 6.4 keV Fe K-alpha line in NGC 4151 to be less than 160 eV FWHM (7,500 km/s), in contrast with former measurements of the line width. Also, we have limited information on the shape of the line profile. In addition to the strong narrow Fe K-alpha feature, we detect weaker broad residuals between 5-8 keV.

The Batuski-Burns list of candidate superclusters was searched for X-ray emission in the HEAO 1 A-2 data base. No significant flux in excess of integrated member cluster emission was detected in directions associated with estimated supercluster centroids; a 3 sigma upper limit to the mean individual excess flux is 5 x 10 to the -12th ergs/sq cm/s. Implications of this bound are discussed in terms of fainter member clusters, hot diffuse gas, and active and normal galaxies. Prospects of supercluster observations related to future X-ray missions are also outlined.

Expectations for the angular correlation function of intensity fluctuations of the extragalacitc 2-10 keV X-ray background are discussed in relation to the two-point spatial correlation functions, xi(r), of X-ray sources. A simple analytic formula for the amplitude of intensity correlations, Gamma(theta), holding in the low-redshift, small-separation approximation, is derived. The HEAO 1 A-2 upper limits on Gamma(theta) have been exploited to derive constraints on the local xi(r) functions of rich clusters of galaxies, of AGNs, and on the AGN-cluster cross-correlation, as well as on evolution of the correlation functions with cosmic time. X-ray data are found to be compatible with the Bahcall and Soneira estimates of xi(cluster-cluster) as well as with the results of recent studies of quasar clustering.

The diffusive streaming of 1.3- to 2.3-MeV per nucleon protons has been found to be predominantly toward the sun during periods between prompt solar particle events. This sunward streaming occurs for essentially all proton intensities from

We have analyzed the HEAO-1 A2 all-sky survey data to investigate the autocorrelation function of the surface brightness fluctuations of the extra-galactic 2–10 keV X-ray background on angular scales ranging from 3° to 27°. No significant signal has been detected on any scale. The derived upper limits set important bounds on correlated emission on scales ≥ 10 Mpc. X-ray data are found to be compatible with optical estimates of the two-point spatial correlation function of rich clusters of galaxies and with recent predictions for their cosmological evolution. Constraints on clustering of Active Galactic Nuclei (AGNs) and on its dependence on cosmic time are analyzed in the light of results of recent optical studies. We also discuss bounds on very large scale structures, on correlations between AGNs and clusters and between clumps of hot gas.

HEAO 1 A-2 data are used to determine hard X-ray fluxes, or upper limits, for complete optically selected samples of active and normal galaxies, in order to estimate or to constrain their local X-ray luminosity functions. It is found that the luminosity function of Seyfert nuclei must flatten down drastically shortly below the observational limit of Piccinotti et al (1982); little can be added by dwarf active nuclei hidden in otherwise normal galaxies. Also analyzed is the possible contribution to the X-ray background from galaxies with strong star-formation activity, in the light of the possibility of a substantial cosmological evolution suggested by recent radio and IRAS data. 94 refs.

Studies of the HEAO–1 A2 all–sky survey data have established that the level of anisotropy of the extragalactic X–ray background (XRB) is relatively low: –The cell–to–cell XRB intensity variations can be entirely accounted for by Poisson fluctuations in the space distribution of known classes of sources; the 90% confidence upper limit to any additional contribution on a scale of 26 square degrees is 2.3% (Shafer and Fabian 1983).–No significant correlations of XRB intensity fluctuations appear to be present; the formal 90% confidence upper limit on the amplitude of autocorrelations, relative to the mean background intensity, for an angular scale of 3° is Γ(3°) ≤ 1.9 × 10−2 (Persic et al. 1988).

It has been found that except during the onset of prompt solar particle events the diffusive flow of 1.3 to 2.3 MeV protons at 1 AU is predominantly sunward. The anisotropy of the proton intensity has been measured with the Caltech Electron/Isotope Spectrometer aboard IMP-7 for periods between prompt solar particle events from 72/273 to 74/2. The diffusive anisotropy, which has been determined by subtracting the independently determined convective anisotropy from the observed anisotropy, is predominantly directed toward the sun with a mean radial component of 14%. This sunward diffusion is typical of intensities from 0.012 to 1.2 (cm^² sec sr MeV)^(−1) for 1.3 - 2.3 MeV protons and indicates that a positive radial gradient is characteristic of these modestly enhanced fluxes. The direction of the flow is opposite to that which would be produced by previously proposed models which involve a continuous solar source for the observed particles. A steady-state propagation model which includes adiabatic energy loss with particle injection beyond 1 AU produces the average observed anisotropy for κ_rr∼4 × 10^20 cm^² sec^(−1).

A 13 hr observation of 2S0142+61 on 1984 August 27 by EXOSAT shows the X-ray flux of 2SO142+61 to be modulated with a period of 1456+/-6 s. The 1–10 keV spectrum is two component with a ~0.7 keV thermal and 0.0 energy index power law, with 30% of the total luminosity in the thermal component. The spectrum is absorbed by ~1x1022 H cm-2. Only the hard component is pulsed with a 3 to 10 keV peak to mean amplitude of 35%. Below 2 keV the modulation is less than a few percent. The total 1–10 keV lominosity is 3.5x1032 erg s-1 for a distance of 100 pc. Possible optical counterparts are discussed.

The HEAO 1 A-2 all-sky survey data have been analyzed to investigate the autocorrelation function of the surface brightness fluctuations of the extragalactic 2-10 keV X-ray background on angular scales ranging from 3 to 27 deg. The derived upper limits are compatible with optical estimates of the spatial correlation function of Abell's clusters and set interesting constraints on possible AGN clustering.

A new interplanetary network (IPN) is made possible by the modication of the NEAR mission, now at 2 AU distance. With Ulysses and the near-Earth GRB monitors, this fully long-baseline network will produce GRB localizations at a rate of about one per week, with ac- curacies varying from several to tens of arc minutes. Given the delays inherent in the collection of deep space data, high-precision alerts with delays under one day should be possible at a rate of one to several per month. An auto- matic analysis system is being developed to optimize the process.

It is shown that in addition to many Seyfert galaxies and quasars, N galaxies are also powerful X-ray sources. X-ray emission has been discovered from all six N galaxies in the 3C radio catalogue with redshifts less than 0.06 and from the N galaxy Pic A. Since many of the N galaxies possess compact radio components, it is suggested that the principle cause of X-ray emission may be the synchrotron self-Compton process. An alternate theory suggests that X-rays may be generated by gas clouds colliding with velocities of the order of the Doppler width of the broad lines.

The hypothesis that normal galaxies are on the average more luminous in the X-ray region than the Milky Way galaxy or M31 and therefore are possible candidates for the low-luminosity sources of the 2 to 60 keV extragalactic diffuse background is tested. Data from the A-2 detectors on the HEAO-1 spacecraft were examined for emission from positions coincident with 76 selected normal galaxies, and upper limits to the average galactic luminosity for various luminosity distributions resulting in the observed count rate distribution were determined. For uniform and exponential galactic luminosity distributions, limits of 2.7 x 10 to the 38th erg/sec and 3.4 x 10 to the 38th erg/sec, respectively, at the 90% confidence level were obtained. It is shown that the Hubble-constant-independent upper limit to galactic emissivity is less than 1% of the diffuse background emissivity, indicating that normal galaxies are not responsible for the diffuse X-ray background and have luminosities comparable to that of the Galaxy.

Results are reported for a systematic search with the A-2 experiment aboard HEAO 1 for X-ray emission from 28 radio sources that were actually bursting at the epoch of the X-ray observations. Two of these sources are found to lie within the positional errors of X-ray sources: the moderately redshifted quasars NRAO 140 and NRAO 530. The positions of 30 historically variable radio sources that were not active at the time of the search are compared with those of detectable X-ray sources, but no X-ray emission is detected from any of these positions. The implications of the results are discussed in terms of models for the radio emission from compact extragalactic sources. Several possible explanations are presented for the general absence of Compton X-ray emission from the bursting radio sources surveyed.

HEAO 1 A-2 and Einstein Solid State Spectrometer (SSS) observations of SMC X-1 are presented. An unpulsed soft component is found with a blackbody temperature of 0.16 keV and an area for the emission region of 10 to the 15th to 10 to the 17th sq cm. The hard X-ray component is pulsed; the phase-averaged spectrum is a power law with alpha of about 0.5 up to 17 keV, above which it steepens. The SSS sets an upper limit of less than 4 x 10 to the 21st H/sq cm to any absorption, and is consistent with that expected from the wind of Sk 160. Absorption dips with a timescale of several hundred seconds are seen immediately following an eclipse exit, and are probably caused by inhomogeneities in the wind of Sk 160.

X-ray emission has been detected from PG 1658 + 441, a hot, isolated, magnetic white dwarf. The source was first detected in an Einstein IPC observation and was later identified in an Exosat channel multiplier array observation. Both imaging observations were motivated by an attempt to find the optical counterpart to the HEAO 1 soft X-ray source H1659 + 44. Spectral analysis, however, indicates that H1659 + 44 and PG 1658 + 441 are unrelated. The broad-band spectrum of this DA white dwarf can be explained as emission from a homogeneous, high-gravity, pure hydrogen atmosphere with a temperature near 28,000 K. The observations of PG 1658 + 441 support the suggestion that a correlation exists between temperature and helium abundance in white dwarf atmospheres.

The discovery of an extended X-ray source identified with a cluster of galaxies at low galactic latitude is reported. The source, designated the Ophiuchus cluster, was detected near 4U 1708-23 with the HEAO 1 Scanning Modulation Collimator, and identified with the cluster on the basis of extended X-ray size and positional coincidence on the ESO/SRC (J) plate of the region. An X-ray flux density in the region 2-10 keV of approximately 25 microJ was measured, along with an X-ray luminosity of 1.6 x 10 to the 45th ergs/sec and an X-ray core radius of approximately 4 arcmin (0.2 Mpc) for an assumed isothermal sphere surface brightness distribution. The X-ray spectrum in the range 2-10 keV obtained with the HEAO 1 A-2 instrument is well fit by a thermal bremsstrahlung model with kT = 8 keV and a 6.7-keV iron line of equivalent width 450 eV. The steep-spectrum radio source MSH 17-203 also appears to be associated with the cluster, which is the closest and brightest representative of the class of X-ray clusters with a dominant central galaxy.

Spectral studies of LMC X-3 using the HEAO 1 A-2 experiment and the Einstein Solid State Spectrometer show that the X-ray spectrum is extremely soft relative to the vast majority of galactic accretion-driven X-ray sources, but similar to that of black hole candidates in their 'high state'. Rapid approximately 1 s flickering comparable to that seen from Cyg X-1 in its low state was not detected. In the 1977-1979 interval LMC X-3 was for most (if not all) of its time in a 'high state'. The fact that several other steady and transient X-ray sources also have similarly soft X-ray spectra and should be regarded as potential black hole candidates is noted. The spectra of these sources are not well described by any one simple model.

The all-sky data base acquired with the HEAO A-2 experiment was searched for X-ray emission on a variety of metagalactic size scales which were either predicted or previously detected. Results in the 0.2-60 keV energy range are presented. The optically richest clusters, including those from which a microwave decrement were observed, appear to be relatively underluminous in X-rays. Observations of Abell 576 show its luminosity to be less than earlier estimates, and moreover less than the luminosity predicted from its microwave decrement, unless the intracluster gas is a factor of approximately 10 hotter than in typical clusters. Near SC0627 there are two X-ray sources, and the identification of the dominant source with SCO627 is probably incorrect. New spectral observations of Abell 401 and 2147, possible superclusters, reveal that they have typical cluster spectra with iron line emission.

The diffuse 2-60 keV X-ray background has a galactic component clearly detectable by its strong variation with both galactic latitude and longitude. This galactic component is typically 10 percent of the extragalactic background toward the galactic center, half that strong toward the anticenter, and extrapolated to a few percent of the extragalactic background toward the galactic poles. It is acceptably modeled by a finite radius emission disk with a scale height of several kiloparsecs. The averaged galactic spectrum is best fitted by a thermal spectrum of kT about 9 keV, a spectrum much softer than the about 40 keV spectrum of the extragalactic component. The most likely source of this emission is low luminosity stars with large scale heights such as subdwarfs. Inverse Compton emission from GeV electrons on the microwave background contributes only a fraction of the galactic component unless the local cosmic ray electron spectrum and intensity are atypical.

A search for new hard X-ray sources using data from the first complete view of the sky with the HEAO-A2 experiment discovered 47 new sources, detected 7 sources recently discovered with other experiments, and significantly reduced the size of the error boxes for 6 previously known sources. Intensities and error boxes are given for each of these sources; identifications are suggested when an error contains an object similar to known X-ray sources. The new identifications consist of seven Type 1 Seyfert galaxies, including two whose Seyfert characteristics were discovered due to their location in an X-ray error box; one intermediate Seyfert galaxy; three Abell clusters; five N-galaxies; two bursting radio sources; and an additional three nearby galaxies with bright nuclei and narrow emission lines.

Results are presented for HEAO A-2 pointed observations and Ariel 5 A11-Sky Monitor observations of the X-ray transient 4U 0115 + 63. The transient source pulses with a period of 3.6136 s + or - 0.0004 s, has a hard spectrum typical of an X-ray binary pulsar, and has a broad iron line emission feature. A discussion of the transient behavior is given, and inferences are made concerning the nature of the X-ray source based on the pointed data.

The paper presents the 2-50-keV X-ray spectra and time variability information on seven Seyfert 1 galaxies NGC 3783, NGC 4151, NGC 5548, NGC 6814, MK 509, MCG 8-11-11, and ESO 141-G55, obtained with the A2(2) experiment on HEAO 1. It is concluded that the spectra of Seyfert 1 galaxies can be well represented by flat power laws of high-temperature thermal breamsstrahlung models with relatively low column densities.

The number density of serendipitous sources in galactic plane Einstein Observatory IPC fields are compared with predictions based on the intensity of the HEAO-1 A2 unresolved hrd X-ray galactic ridge emission. It is concluded that theoretically predicted X-ray source populations of luminosity 8 x 10 to the 32nd power to 3 x 10 to the 34th power ergs s have 2 KeV to 10 KeV local surface densities of less than approximately .0008 L(32) pc/2 and are unlikely to be the dominant contributors to the hard X-ray ridge. An estimate for Be/neutron star binary systems, such as X Persei, gives a 2 keV to 10 keV local surface density of approximately 26 x 10 to the -5 power L(32) pc/2. Stellar systems of low luminosity, are more likely contributors. Both RS CVn and cataclysmic variable systems contribute 43% + or - 18% of the ridge. A more sensitive measurement of the ridge's hard X-ray spectrum should reveal Fe-line emission. We speculate that dM stars are further major contributors.

A sample of 25 QSOs was used to investigate the average spectrum between the soft X-ray energy band of the Einstein Observatory image proportional counter, and the higher energy band of the HEAO 1 A2 experiment. The spectrum is similar to thoe exhibited by Seyfert galaxies and narrow emission line galaxies above 2 keV. The spectrum is soft enough that if these objects are typical of the higher redshift, more radio-quiet QSOs, then it is possible to exclude QSOs as being the dominant origin of the diffuse X-ray background.

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.

Numerous observations of SS 433 were obtained with the Einstein X-ray Observatory over an 18 month period from 1979 March through 1980 October. MPC (as well as imaging) data from these observations show that the central object in SS 433 is variable in intensity and spectrum on a wide range of time scales. Flares appear to be correlated with the 13 day binary period, and may be more numerous at particular phases of the 164 day period. No evidence for variability on time scales less than 5 minutes is seen, suggesting the central X-ray source is extended and that the compact object itself is not directly visible. A model for SS 433 is suggested wherein the companion star has a spin misaligned with the orbital angular momentum. The volume of the Roche lobe reaches a minimum twice per binary orbit, giving rise to enhanced accretion which results in X-ray and radio flares. Additional constraints imposed by the X-ray and optical data suggest the compact object in SS 433 is an approximately 10-solar-mass black hole.

An all-sky survey of X-ray sources was performed, complete to a limiting sensitivity of 3.1 x 10 to the -11 ergs/sq cm/s in the 2-10 keV band. The complete sample has allowed construction of luminosity functions based on a flux-limited sample for clusters of galaxies and active galactic nuclei. Integration of the best-fit luminosity functions indicates that clusters of galaxies contribute about 4% of the 2-10 keV DXRB, and active galactic nuclei about 20%. It is predicted that many of the objects seen in the deep survey should be local, relatively low luminosity active galactic nuclei and clusters of galaxies.

The X-ray source H1908+050 (=4U 1908+05=A1909+04) was observed for three 6 day periods in 1977 and 1978 with the HEAO A-2 experiment. Because of the positional error box and variability of the source, the unusual emission-line object and variable radio source SS 433 has been suggested as the potical counterpart. The X-ray luminosity of the source varied by a factor of approx.2 on a time scale of 6 months, and the spectrum of the object is consistent with either a power law of photon index GAMMA of 2.1 or with 14.3 keV thermal bremsstrahlung emission with a approx.575 eV equivalent-width iron line. These X-ray characteristics argue against the source being extragalactic, but do not uniquely identify the type of source. The measurements are consistent with emission from a white dwarf with approx.10/sup 8/ gauss magnetic field, but are also similar to the X-ray emission sometines seen from Cir X-1. A search has been made for X-ray emission from similar radio sources, but no new X-ray sources were detected. A previously known source, A1850+00, is a possible counterpart for one of these radio sources.

A sample consisting primarily of radio bright quasars was observed in X-rays with the Einstein Observatory for times ranging from 1500 to 5000 seconds. Detected sources had luminosities ranging from 0.2 to 41.0 x 10 to the 45th power ergs/sec in the 0.5 to 4.5 keV band. Three of the fourteen objects which were reobserved showed flux increases greater than a factor of two on a time scale greater than six months. No variability was detected during the individual observations. The optical and X-ray luminosities are correlated, which suggests a common origin. However, the relationship (L sub x is approximately L sub op to the (.89 + or - .15) found for historic radio variables may be significantly different than that reported for other radio bright sources. Some of the observed X-ray fluxes were substantially below the predicted self-Compton flux, assuming incoherent synchrotron emission and using VLBI results to constrain the size of the emission region, which suggests relativistic expansion in these sources. Normal CIV emission in two of the sources with an overpredicted Compton component suggests that although they, like BL Lac objects, have highly relativistic material apparently moving at small angle to the line of sight, they have a smaller fraction of the continuum component in the beam.