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A significant fraction of all stars are in binaries. It is thus reasonable to examine the possibility that the progenitor of SN 1987A was a component of a binary system. We here consider some of the ranges of parameter space in which binary evolution produces progenitors that are applicable to models of SN 1987A [1, 2, 3]. Other binary models have been proposed by FABIAN et al. [4] and CHEVALIER and SOKER [5]. Such models may help to explain several of the anomalies of this supernova, including the blue color of the progenitor, the asymmetries in the ejecta, the barium anomaly, and the mystery spot (see [1, 2, 3] for further discussion and references). Unlike many single-star models (see [1, 2, 3] for references), the fits of these models to the observations do not rely on the assumption of low metallicity, a non-standard treatment of convection, and/or the ad hoc stipulation of severe mass loss from the presupernova star. The binary models presented here make definite predictions that can be checked against observations; moreover, the models are sufficiently general that the results may be relevant to other supernovae as well.

The existence of a new class of astrophysical object, luminous supersoft X-ray sources, has been established through ROSAT satellite observations and analysis during the past approximately 3 yr. Because most of the radiation emitted by supersoft sources spans a range of wavelengths readily absorbed by interstellar gas, a substantial fraction of these sources may not be detectable with present satellite instrumentation. It is therefore important to derive a reliable estimate of the underlying population, based on the approximately 30 sources that have been observed to date. The work reported here combines the observational results with a theoretical analysis, to obtain an estimate of the total number of sources likely to be present in M31, the Magellanic Clouds, and in our own Galaxy. We find that in M31, where approximately 15 supersoft sources have been identified and roughly an equal number of sources are being investigated as supersoft candidates, there are likely to be approximately 2500 active supersoft sources at the present time. In our own Galaxy, where about four supersoft sources have been detected in the Galactic plane, there are likely to be approximately 1000 active sources. Similarly, with about six and about four (nonforeground) sources observed in the Large (LMC) and Small Magellanic Clouds (SMC), respectively, there should be approximately 30 supersoft sources in the LMC, and approximately 20 in the SMC. The likely uncertainties in the numbers quoted above, and the properties of observable sources relative to those of the total underlying population, are also derived in detail. These results can be scaled to estimate the numbers of supersoft sources likely to be present in other galaxies. The results reported here on the underlying population of supersoft X-ray sources are in good agreement with the results of a prior population synthesis study of the white dwarf accretor model for luminous supersoft X-ray sources. It should be emphasized, however, that the questions asked in these two investigations are distinct, that the approaches taken to answer these questions are largely independent and that the findings of these two studies could in principle have been quite different.

Luminous supersoft X-ray sources, with characteristic luminosities of approximately 10(exp 38) ergs/s and temperatures, kT, of approximately 35 eV, have been established as a new and distinct class of X-ray source through recent Roentgen Satellite (ROSAT) observations. Several possible physical models have been proposed for these sources. One promising scenario (van den Heuvel et al. 1992) involves mass transfer, which is unstable on a thermal timescale, from a main-sequence or subgiant donor star onto the surface of a white dwarf. For a narrow range of accretion rates, steady nuclear burning of the accreted matter can take place. This process can provide the high luminosities and the correct range of temperatures observed in the supersoft sources. However, given the limited range of mass transfer rates that are consistent with this phenomenon, it is far from obvious that a sufficient population of such systems exists in galaxies such as our own, M31, and the Magellanic Clouds, in order to account for the large number of supersoft sources which can be inferred from present observations. This work addresses the population question in detail, through a Monte Carlo simulation of the formation and evolution of such systems, which starts with zero-age primordial binaries. In order to evolve into close binary systems which contain a white dwarf component and a companion transferring mass at a rate within the requisite narrow range, a binary system must undergo a specific progression of evolutionary steps. We find that a sufficient subset of our initial binaries evolve to become systems with the requisite properties, so that they can account for the population of supersoft sources that is inferred from observations. In particular, we find that there should be more than 1000 systems in the Galaxy today with properties that very closely match those of the observed supersoft sources. From our models, we find expected luminosities, white dwarf effective temperatures, and orbital periods in the ranges of 10(exp 37) - 10(exp 38) ergs/s, (1-5) x 10(exp 5) K, and 8 hr-1.4 days, respectively. The masses of the white dwarf and donor star are expected to lie in the range of 0.7-1.05 solar mass and 1.3-2.7 solar mass. Finally, we discuss the role that supersoft X-ray sources may play as the progenitors of Type Ia supernovae, and estimate the rate of production via this channel.

We have studied the number of cataclysmic variables (CVs) that should be active in globular clusters during the present epoch as a result of binary formation via two-body tidal capture. We predict the orbital period and luminosity distributions of CVs in globular clusters. The results arebased on Monte Carlo simulations combined with evolution calculations appropriate to each system formed during the lifetime of two specific globular clusters, omega Cen and 47 Tuc. From our study of these two clusters, which represent the range of core densities and states of mass segregation that are likely to be interesting, we extrapolate our results to the Galactic globlular cluster system. Although there is at present little direct observational evidence of CVs in globular clusters, we find that there should be a large number of active systems. We predict that there should be more than approximately 100 CVs in both 47 Tuc and omega Cen and several thousand in the Galactic globular cluster system. These numbers are based on two-body processes alone and represent a lower bound on the number of systems that may have been formed as a result of stellar interaction within globular clusters. The relation between these calculations and the paucity of optically detected CVs in globular clusters is discussed. Should future observations fail to find convincing evidence of a substantial population of cluster CVs, then the two-body tidal capture scenario is likely to be seriously constrained. Of the CVs we espect in 47 Tuc and omega Cen, approximately 45 and 20, respectively, should have accretion luminosities above 10(exp 33) ergs/s. If one utilizes a relation for converting accretion luminosity to hard X-ray luminosity that is based on observations of Galactic plane CVs, even these sources will not exhibit X-ray luminosities above 10(exp 33) ergs/s. While we cannot account directly for the most luminous subset of the low-luminosity globular cluster X-ray sources without assuming an evolutionary pattern that is different from that of the majority of CVs in the disk, we are able to account for all of the observed lower luminosity subset of these sources, many of which have been recently discovered through ROSAT observations. In order for our predicted integrated cluster X-ray luminosities to be consistent with observational upper limits, the relation between accretion and X-ray luminosities should be something like that inferred from the Galactic plane population of CVs. Our calculations predict a large number of systems with L(sub acc) is less than 10(exp 32) ergs/s. Although our calculations imply that globular clusters should have an enhancement of CVs relative to the number thought to be present in the Galactic disk, this enhancement is at most roughly an order of magnitude, not comparable to the factor of approximately 100 for low-mass X-ray binaries (LMXBs).

The results are reported of three observations of the binary X ray pulsar SMC X-1 with the Ginga satellite. Timing analyses of the 0.71 s X ray pulsations yield Doppler delay curves which, in turn, provide the most accurate determination of the SMC X-1 orbital parameters available to date. The orbital phase of the 3.9 day orbit is determined in May 1987, Aug. 1988, and Aug. 1988 with accuracies of 11, 1, and 3.5 s, respectively. These phases are combined with two previous determinations of the orbital phase to yield the rate of change in the orbital period: P sub orb/P sub orb = (-3.34 + or - 0.023) x 10(exp -6)/yr. An interpretation of this measurement and the known decay rate for the orbit of Cen X-3 is made in the context of tidal evolution. Finally, a discussion is presented of the relation among the stellar evolution, orbital decay, and neutron star spinup time scales for the SMC X-1 system.

The evolution of low-mass X-ray binary systems is calculated with the inclusion of heating of the secondary star by the X-radiation from the primary. The secondary is assumed to be nonsynchronously rotating with the orbit, so that the X-ray heating may be taken to be approximately uniform over its surface. Due to the shadowing effect of a postulated accretion disk, only a portion of the X-ray flux reaches the secondary star. The evolution of binary systems with secondary stars of initial mass 0.4 and 1 M ⊙ is computed

The results of a 2.4 day observation of the binary X-ray pulsar LMC X-4 with the Ginga satellite are reported. A high-quality X-ray spectrum which includes an Fe emission line with an equivalent width of 0.18 keV is presented. Timing analyses of the 13.5 s X-ray pulsations yield a Doppler delay curve, which, in turn, provides the most accurate determination of the LMC X-4 orbital parameters available to date. The phase of the 1.4 day orbit is determined with an accuracy of ∼60 s. This phase is combined with four previous determinations of the orbital phase to yield an estimate of the rate of change in the orbital period of (1.1 ± 0.8)×10 −6 1/yr

Results are reported for SAS 3 observations of 22 bursts from the X-ray source designated MXB 1837+05. Assuming that all the bursts come from one source, the source position is determined to be right ascension (1950) 18 hr 37.9 min, declination (1950) 5 deg 4.2 min. Integrated burst intensities are listed along with ratios of counts in different energy channels, and it is found that there are significant variations in these ratios from burst to burst. The bursts are also shown to exhibit a variety of temporal structures (including double peaks) and changes in spectral hardness. No regularity was detected in the burst occurrence times during one observing period, but four bursts during another period seemed to recur at regular intervals of about 6.3 hr. It is concluded that an intensity-interval correlation similar to that for a rapid burster does not exist for MXB 1837+05 and that this source is probably identical with the relatively strong and steady source Ser X.1.

The binary model of gamma ray burst sources wherein the bursts are emitted by a collapsed object in a close-binary stellar system and a small fraction of the gamma radiation is reprocessed into optical radiation in the surface layers of a companion star is considered, and it is concluded that the model is viable. In particular, under the assumption that the optical flashes discovered by Schaefer (1981) and Schaefer et al. (1984) were produced by gamma-ray bursts of about the same intensity as those observed, it is found that nearby binary systems with secondaries whose masses are less than about 0.06 solar mass can fit all the observational constraints for the three optical/gamma-ray pair events.

Most evidence on X-ray emission from the vicinity of Be stars concerns the Be/X-ray binaries. Presently some 20 of these systems are known, making them the most numerous class of massive X-ray binaries. Evidence for the binary nature of these systems comes from (i) Doppler modulation of X-ray pulse periods, (ii) periodic X-ray flaring behavior, and (iii) correlated optical and X-ray variability. The correlation between X-ray pulse period and orbital period found by Corbet (1984) can potentially provide important information on the densities and velocities in the circumstellar disks of Be stars.Evolutionary models indicate that the Be/X-ray binaries represent a later stage in the evolution of normal close binaries with initial primary masses predominantly in the the range 8 to 15 M⊙ . These models indicate that also a class of slightly less massive Be star binaries should exist in which the compact companions are white dwarfs. Be-type blue stragglers in galactic clusters may be such systems.

The present state of empirical knowledge about neutron-star masses is reviewed. It is shown how the mass function of a pulsar-containing binary system can be inferred from measurements of the pulsation period and the projected semimajor axis of the pulsar orbit plus independent information concerning the inclination of the orbital plane, the mass of the companion star, or both. Relevant observational properties, the type of information used to constrain the pulsar mass, and the range of allowable pulsar masses are summarized for the binary systems 3U 0900-40, Cen X-3, SMC X-1, Her X-1, and PSR 1913+16. It is found that as long as the general theory of relativity is correct, neutron-star masses should range from about 1.4 to 1.9 solar masses if the companion is a normal white dwarf or should be less than about 1.9 solar masses if the companion is some other object. It is concluded that these mass estimates are entirely consistent with the predictions of nuclear physics theory.

A number of evolutionary scenarios have been proposed that lead to the formation of binary systems consisting of a degenerate dwarf in orbit with a neutron star. In fact, most degenerate dwarfs in close-binary systems are probably the cores of evolved stars whose envelopes have been stripped by one or more episodes of common-envelope evolution. Once the envelope has been removed, the newly exposed core of the giant will have an effective temperature and radius that are considerably larger than the corresponding quantities in an older, highly degenerate dwarf. It is important for at least two reasons to evaluate the subsequent cooling history of such objects: (i) For detached binaries, we want to be able to infer from the current effective temperature and luminosity of the degenerate dwarf the elapsed time since the core of its progenitor giant was exposed, (ii) For semi-detached binaries, we must know the evolution of the radius of the degenerate dwarf in order to compute important relationships among the orbital period and its rate of change, the mass of the degenerate dwarf, and the mass-transfer rate.

It is proposed that the progenitor of supernova 1987A was a previously undetected red star in orbit about a blue supergiant. The progenitor was the remnant of an asymptotic-branch giant that had lost most of its hydrogen-rich envelope to its blue companion by type C mass transfer. A detailed evolutionary model strongly supports the feasibility of this proposition. It is found that the original mass of the supernova precursor was 10-15 solar (unless a large fraction of the mass was ejected from the binary sytem), and its final mass, just before the supernova event, was 3-6 solar. The system remained bound, with a new orbital period of 3-10 yr and an eccentricity of 0.1-0.4. This picture can provide plausible qualitative explanations for several anomalies in the observational properties of this supernova.

The pulsing X-ray source 4U 1626-67 is an accreting neutron star in a binary system with a very low mass companion. The source was observed by Exosat continuously for 23 hr on March 30-31, 1986 UT. It is found that, if the orbital inclination angle equals 90 deg, the optical companion star has a mass of less than about 0.002 solar mass; however, it is found that a companion star mass of greater than about 0.06 solar mass is required if gravitational radiation is responsible for driving the mass transfer in this system. Also presented are results on flaring activity in the system on time scales of about 1000 s, the energy-dependent pulse profiles, and the pulse period history over the past decade.

The early history of the development of our understanding of neutron stars has been described by others, and we summarize it only briefly here. Following an early speculation by Baade & Zwicky ( 1934) soon after the discovery of the neutron in 1932, Oppenheimer & Volkoff(1939) presented a classic analysis of the theoretical viability of neutron stars, based on the general theory of relativity and the nuclear physics that was then known. A number of further theoretical studies were published during the next three decades, but it seemed that neutron stars might be virtually unobservable and thus remain little more than a theorist's curiosity piece. In a prophetic paper, Pacini (1967) noted that a rotating neutron star with a magnetic field whose axis was misaligned with the rotation axis should emit intense magnetic dipole radiation. Almost immediately thereafter (but quite independently), Hewish et al. (1968a,b) announced the discovery of radio pulsars. For a brief period, several theoretical models for the pulsar phenomenon were in contention. However, the discovery of the pulsar NP 0532 in the Crab Nebula (Staelin & Reifenstein i968, Comella et al. 1 969), followed by a notably straightforward set of observations and theoretical arguments, soon clinched the case for neutron stars (Gold 1969a).1 (For a review of these remarkable developments, see Gold 1969b.)

Two X-ray burst sources have been discovered in Aquila with the aid of the SAS 3 X-ray Observatory; MXB 1906 + 00 and Aql MXB. The present paper reports on source positions, spectra, time structure, and burst energy. Five bursts were detected from MXB 1906 + 00, and the data are shown to be consistent with the assumption that there was a burst about every 8.9 hr. A comparison of raw counting data for three bursts indicates that the bursts were detected in the energy range from 1.3 to 19 keV and that the spectrum softened during burst decay. The spectrum of the one burst observed from Aql MXB is found not to soften during burst decay. It is suggested that MXB 1906 + 00 and the previously known 'steady' source A 1905 + 00 are very likely to be the same source and that the ratio of time-averaged 'steady' luminosity to time-averaged burst luminosity would be approximately 80.

Be star binaries with neutron star companions are shown to constitute a major class of X-ray sources. Some general observational and interpretive techniques of X-ray astronomy are reviewed. Data for 12 Be/X-ray binary systems are summarized. The Be/X-ray binaries are found to be systematically wider systems, with lower-mass primaries, and with significantly more transient behavior than the “standard” massive X-ray binaries such as Cen X-3 and SMC X-1. The difference between the two types of X-ray binaries is explained in the context of slightly different evolutionary scenarios for the progenitor binaries. The “standard” massive X-ray binaries result from wind-mass-loss dominated evolution of very massive close binaries, while Be/X-ray binaries probably result from mass-transfer dominated evolution of systems with primary masses ≲ 20 M⊙. The implications of the X-ray observations of Be/X-ray binaries for Be stars in general are discussed.

An analysis of the nuclear-active particle component of extensive air showers has yielded evidence that the chemical composition of primary cosmic rays at ${10}^{15}$ eV cannot consist solely of protons or solely of very heavy nuclei. The data are consistent with the mixed composition observed at lower energy (\ensuremath{\sim}${10}^{11}$ eV).

X ray sources identification and position measurements near galactic center on basis of rocket experiments

Low energy X ray spectra of Sco X-1 and Sagittarius sources measured by Be and Al window proportional counters during rocket flight

A sealed Ti window proportional counter sensitive to x radiation in the energy range 0.35–0.45 keV and >1.5 keV is described. Measurements of the Ti mass absorption coefficients and a graphical summary of the literature values are presented. For a proportional counter with a 930 μg/cm2 (2.1 μ) Ti window, the peak efficiency at 0.45 keV is found to lie between 4.6% and 7.1%. An application in x‐ray astronomy involving a rocket observation of Sco X‐1 is discussed.

As X-ray astronomy enters the Einstein era when faint, distant, and exotic X-ray sources are being investigated, we thought it might be useful to review some of the progress made over the past decade on a class of relatively nearby objects that have contributed richly to our understanding of astrophysics — the binary X-ray pulsars. We shall touch briefly on three general topics related to X-ray pulsar research: (1) pulse profiles, (2) studies of pulse periods, and (3) orbital determinations and the evaluation of binary system parameters. We shall also discuss three special topics of current interest: (1) the apsidal motion test in X-ray binaries; (2) 4U1626-67 and the nature of highly compact X-ray binary systems; and (3) searches for new X-ray pulsars in the Einstein era. Most of the data that we shall invoke were obtained with the Uhuru, Copernicus, Ariel 5, SAS-3, 0S0-8, and HEAO-1 satellites.

Results of the first numerical evolutionary calculations for very low-mass stars with ages up to the age of the Galaxy are presented. The calculations shed new light on the nature of the recently discovered object VB 8B, the companion to Van Biesbroeck's star no. 8, and support the identification of this object as a low-mass star in which hydrogen burning was never able to establish thermal equilibrium. For plausible ages of this binary stellar system, the mass of VB 8B is estimated to be in the range 0.04-0.08 solar mass. The object is supported primarily by degenerate electron pressure; its present values of central density and temperature are found to be 500-2000 g/cu cm and 1.0-1.5 million K. An orbital period of more than about 40 yr is predicted for the binary system. The presented evolutionary tracks are also applicable to the interpretation of observations of other very low-luminosity dwarfs.

SAS 3 observations reveal a pulsation period of 3.61 sec for the transient X-ray source 4U0115+63. Positional measurement is accurate to approximately 30 arc s, and has led to the likely identification of an optical counterpart. The intensity of the pulses, as reported on 5.9 January 1978, is given as approximately 1.7 times that of the Crab Nebula (1-27 keV). Spectral information was also obtained from the ratios of counting rates in the first three energy channels of the center slat collimator detector (1-27 keV). Two classes of models are proposed to explain the transient nature of the X-ray sources: (1) episodic mass transfer in a binary system, and (2) eccentric binary orbits.

After previous searches for radio pulsars in globular clusters1,2, a radio pulsar with a period of 3.054 millisecond has now been discovered in NGC6626 (M28)3. The upper limit of 3×10–17 to the observed period derivative indicates that the pulsar is not in a binary3. Millisecond pulsars are probably 'recycled' old pulsars which have been spun-up through accretion from a binary stellar companion4,5. In a globular cluster such a binary is likely to have formed in a tidally dissipative collision between an old neutron star and a low-mass field star from the cluster. Eventually, a mass-transfer phase ensues and the accretion of only ∼0.1M⊙ from the companion is sufficient to spin up the neutron star to millisecond periods. Later in the history of the binary, it can undergo a catastrophic collision with a passing field star from the cluster, the net result of which may be a neutron star with a massive disk orbiting it. After much of the material is expelled via accretion-generated radiation pressure, only an isolated millisecond radio pulsar remains. We also explore the possibility that accretion from a massive disk is able directly to spin up the neutron star; in this case, however, the predicted number of millisecond pulsars in globular clusters would be ten times the number of bright low-mass X-ray binaries. In the model where the neutron star is spun up in a binary the predicted number of millisecond pulsars is significantly smaller. If the millisecond pulsar in NGC6626 has a magnetic moment similar to that of the other three known millisecond pulsars, the epoch of spin-up must have terminated ≲8×108 yr ago.

An analysis of the accretion process in an X-ray pulsar, whereby angular momentum is transferred to the star and its rotation period is changed, is presented, and an expression for the fractional rate of change of the pulse period in terms of X-ray luminosity and other star parameters is derived. It is shown that observed characteristic spin-up time scales for seven X-ray pulsars strongly support the view that in every source (1) the pulse period reflects the rotation period of a compact object, (2) the accretion is mediated by a disk surrounding the compact object and rotating in the same sense, and (3) the compact object is a neutron star rather than a white dwarf.

A quantitative model is presented to account for the observed features of the binary pulsar PSR1953+53. A lower giant branch star is suggested to have evolved on a nuclear time scale while orbiting a neutron star, with mass transfer to the neutron star commencing when the giant attained its Roche lobe. A radius-core mass relationship was used to examined the processes that occurred after the hydrogen atmosphere was drained off to the neutron star. Tidal dissipation has circularized the orbit of the companion during mass transfer, while the orbit expanded. Accretion torques caused spin-up of the neutron star, which had a magnetic moment of no more than 3 x 10 to the 27th G/cu cm. The drained star became a degenerate dwarf with very faint luminosity, which accounts for no visual companion having been observed to date.

In connection with information considered by Illarianov and Sunyaev (1975) and van den Heuvel (1975), a simple physical model for an X-ray burst source in the galactic disk is proposed. The model includes an unevolved OB star with a relatively weak stellar wind and a compact object in a close binary system. For some reason, the stellar wind from the OB star is unable to accrete steadily on to the compact object. When the stellar wind is sufficiently weak, the compact object accretes irregularly, leading to X-ray bursts.

This article presents the results of an analysis of X-ray data from NP0532. Limits on X-ray pulsations from five galactic X-ray sources and ten radio pulsars are also given.

Pulsar NP 0532 in Crab Nebula observed by rocket and telescope showing strong pulsed X ray signal

The Crab Nebula pulsar, NP 0532, is the only one of the 56 known pulsars which has been observed to pulse in the optical spectrum. Even more spectacular are the vast quantities of pulsed X-rays which it has been found to emit. Soft X-rays in the 1–10 keV region have been observed during four sounding rocket flights (Fritz et al., 1969; Bradt et al., 1969; Boldt et al., 1969; Ducros et al. 1970) and harder X-rays, 25–200 keV, have been detected during two balloon flights (Fishman et al., 1969a, b; Floyd et al., 1969). From the results of these six experiments we summarize the properties of the X-ray pulsations from NP 0532.

Progress made over the last decade in the understanding of the binary X-ray pulsars is reviewed. The characteristics of the pulse profiles of the known binary X-ray pulsars are discussed, and observed variations in pulse period corresponding to the spin-up of the neutron star are considered. Determinations of the orbits and binary system parameters of the binary X-ray pulsars from measurements of pulse arrival times are then examined. Attention is also given to current problems in binary X-ray pulsars, including the apsidal motion test, which allows the determination of the mass distribution within a star, the X-ray source 4U 1626-67, which is believed to be a highly compact binary X-ray source, and the observation of very faint X-ray pulsars with the Einstein Observatory.

The High Energy Transient Experiment (HETE), an international mission currently planned for launch in 1992, is presented. Its prime objective is the multiwavelength study of gamma‐ray bursts with UV, X‐ray, and gamma‐ray instruments. A unique feature of the mission is its capability to localize bursts with several arcsecond accuracy, in near real‐time aboard the spacecraft, and to transmit these positions to the ground, thereby enabling rapid, sensitive follow‐up studies. HETE will be launched from a Get Away Special (GAS) cannister on the Shuttle, utilizing a new spacecraft concept, the ‘‘Cheapsat.’’

Low-mass X-ray binaries (LMXB’s) are luminous X-ray sources which are composed of a late-type optical companion (M ≲ 1 M⊙) and a neutron star (or possibly a black hole). They are often referred to somewhat interchangeably as galactic bulge or Population II sources, or as Sco-like sources after the historical archetype of the group Sco X-1. A schematic of one of the best-studied systems, 4U1626-67, is shown superimposed (to scale) on a photograph of the sun’s disk in Figure 1. This is the smallest known LMXB; the optical companion is slightly larger than the sunspot group and the bow-tie shaped accretion disk is the same size as Saturn’s ring system.

The AXAF CCD Imaging Spectrometer (ACIS) is currently being defined as a possible focal plane instrumentto be flown on the Advanced X -ray Astrophysics Facility (AXAF). The imaging spectrometer consists of anarray of charge coupled devices (CCD's) to be placed at the focus of the AXAF mirrors. The array willprovide high angular resolution (ti 0.5 arc seconds), moderate spectral resolution (ti 150 eV) over the energyrange 0.1 to 10 keV, temporal resolution down to ti 60 p sec, and single photon quantum detection efficiencies of up to 90 %. X -ray sensitivity for a point source exceeds 10 -15 ergs /cm2 sec fof a 105 sec exposure. Whenused in conjunction with the objective gratings, the array will yield wavelength resolution of up to X /4a of about 200. IntroductionThe Advanced X -ray Astrophysics Facility (AXAF) is to be launched in the 1990's as a long -lived 15 years) space observatory for observations of celestial X -ray sources. The principle elements andcharacteristics of the observatory are a set of six nested Wolter Type 1 mirrors of 1.2 m maximum aperturewith a 10 m focal length and an on -axis point spread function of 0.65 arc -second diameter. A set ofobjective gratings immediately behind the mirrors will allow a dispersive spectroscopic capability, and fourfocal surface instrument positions will be provided to accommodate image detectors and spectroscopic

A background optical suppression scheme utilizing a double-beam interferometer-spectrometer with coaligned beams and tailored modulation, transfer functions is presented. The system is designed to enhance the detectability of localized sources in the presence of strong spatially structured background in the IR region of the spectrum. The principles of the double-beam interferometer, several different schemes for tailoring the system MTF, and the results of calculations of the signal-to-noise for a variety of MTFs and types of backgrounds, are discussed. The optical, mechanical and electrical components of the Visidyne laboratory double-beam interferometer are described . The data system and laboratory test source are also discussed. Laboratory measurements demonstrating the spatial and spectral filtering capabilities are presented. (Author)

A technique is described for suppressing the lower spatial frequencies in the object using an optical system with a time -varying MTF. The technique is applicable to imaging radiometers operating in the infrared region. The required variations in the MTF are produced by causing the image to move in a programmed sequenceof small amplitude circular gyrations on the face of the detector. The gyrations are performed at a frequencyhigh compared to the system frame rate. A series of calculations are described which indicate that, at lowspatial frequencies, average suppression ratios of at least 500 to 1 can be achieved with this technique. Introduction This paper discusses a technique of background suppression on an optical level by means of suitably matchedor tailored pairs of modulation transfer functions which, when subtracted from one another, suppress the lowerspatial frequencies in the object scene. This, in turn, enhances the detectability of point sources ortargets in the presence of structured backgrounds. The technique is intended to be applied to image- formingradiometers operating at or near the diffraction limit in the infrared region of the spectrum.Figure 1 shows a somewhat idealized pair of modulation transfer functions of this type. The MTF labeledT (w) initially drops steeply, then levels off, and finally falls to zero at the cutoff frequency, w =1.0.

A technique for background suppression for use in Dual Beam Interferometers and other imaging systems is described. Background suppression is achieved by using pairs of optical systems whose modulation transfer functions match at low spatial frequencies but not at the higher frequencies which characterize a target. Various pairs of systems are discussed, and signal-to-RMS-clutter-leakages are calculated. (Author)

A dual -input radiometer with matched modulation transfer functions is described. The two MTF's are definedby the form of the two entrance pupils, one of which is annular and the other of which is circular. Theradiometer switches alternately between the two pupils by means of a set of polarizing components. By detect-ing only the resulting fluctuations in the image, the lower spatial frequencies in the cbjrct scene aresuppressed. Preliminary measurements of the suppression characteristics as a function of spatial frequency arc presented. IntroductionThe Background Optical Suppression System (BOSS), which has been described in various forms in References 1through 6, uses pairs of matched modulation transfer functions to suppress the range of lower spatial frequen-cies in a structured background, thereby enhancing the detectability of point sources or targets seen againstthat background. The MTF pairs are tailored to match as closely as possible at low spatial frequencies, butmust diverge significantly from each other at higher frequencies. Then, by detecting only fluctuations whenthe two images corresponding to these two MTF's are alternately projected onto the common detector plane, theMTF's are, in effect, subtracted from one another and the lower spatial frequencies in the object are

Congregated near the nuclear bulge of our own Galaxy, and also that of M31, are a handful of bright (≳1037 ergs s-1) persistent X-ray sources. These sources account for most of the total X-ray luminosity of each of these bulges, and their space distribution conforms closely to that of an old disk population (Markers et al. 1977; Van Speybroeck et al. 1979). They have (at least in our own Galaxy) very similar X-ray flux distributions (Jones 1977), and lack the X-ray pulsations frequently found in massive X-ray binaries. Presumably, they are old, low-mass binaries in which the magnetic fields of the neutron stars have decayed.

Magnetic braking is probably an important process in the evolution of low-mass compact binaries, such as cataclysmic variables (CV’s) and low-mass X-ray sources (Verbunt and Zwaan 1981). A simplified stellar evolution code, which describes the mass-losing star as an n= 3/2 polytrope, was developed previously to study the evolution of binaries with a secondary of low mass (0.01 < M/M⊙ < 0.4), when the angular momentum losses are due to gravitational radiation (Rappaport et al. 1982). We have extended this code by using a composite polytrope model for the secondary, wherein the structure of the radiative core is described by an n. = 3 polytrope and the convective envelope by an n = 3/2 polytrope. Our results are described in Rappaport et al. 1983; this paper is a short summary.

A series of laboratory measurements made with a double-beam interferometer having tailored modulation transfer functions is presented. These measurements demonstrate the capability of this instrument to detect faint point sources in the presence of a structured background on the basis of spatial frequency differences and/or spectral differences between the source and the background. Measurements are presented which indicate that this detection process can be carried out at a level of spectral resolution of 1 cm-1 or better.

In this work we carry out a theoretical investigation of a new type of astrophysical gaseous nebula, viz., ionized regions surrounding supersoft X-ray sources. Supersoft X-ray sources, many of which have characteristic luminosities of approximately 10(exp 37)-(10(exp 38) ergs/s and effective temperatures of approximately 4 x 10(exp 5) K, were first discovered with the Einstein Observatory. These sources have now been shown to constitute a distinct class of X-ray source and are being found in substantial numbers with ROSAT. We predict that these sources should be surrounded by regions of ionized hydrogen and helium with properties that are distinct from other astrophysical gaseous nebulae. We present caluations of the ionization and temperature structure of these ionization nebulae, as well as the expected optical line fluxes. The ionization profiles for both hydrogen and helium exhibit substantially more gradual transitions from the ionized to the unionized state than is the case for conventional H II regions. The calculated optical line intensitites are presented as absolute fluxes from sources in the Large Magellanic Cloud and as fractions of the central source luminosity. We find, in particular, that (O III) lambda 5008 and He II lambda 4686 are especially prominent in these ionization nebulae as compared to other astrophysical nebulae. We propose that searches for supersoft X-rays via their characteristic optical lines may reveal sources in regions where the soft X-rays are nearly completely absorbed by the interstellar medium.

Observations made with the Rotation Modulation Collimator system (RMC) have revealed that X-ray source X-4 in the Large Magellanic Cloud (LMC X-4) is most likely part of a binary system. An analysis of the star's coordinates is presented, with attention given to orbital period and flux intensity variations. Stellar mass and orbital inclination angle are estimated for both X-4 and its companion star.

A celestial location with an error circle of radius one minute is reported for the mid-latitude X-ray source 3U 0042+32; comparison of observations from the Ariel-5 and Uhuru satellites with data obtained from two independent rotation modulation collimators yields the precise position. Studies to detect regular pulsations and energy spectra of the X-ray source are also discussed. Analysis of the peak X-ray flux in the error circle, as well as certain distance constraints, suggests that the source of the flux may be a neutron star in a distant galactic binary system having a companion that undergoes episodes of mass transfer due to eruption or orbital eccentricity.