Strong X-ray Sources Research Articles

Composite spectraPaper 10: the equal-mass binary HR 2030 (K0 IIb+B8 IV)

We separate the spectra of the individual components of HR 2030, a sixth-magnitude composite-spectrum binary system, and show that they have types close to K0 IIb and B8 IV, and masses that are equal to within the precision of the measurements (mass The orbit appears to have a very small eccentricity, although reasons are given for believing that such eccentricity is spurious; it has a period of 66 d and an inclination estimated at 30° to the line of sight. Our photometric model of the system confirms the luminosity types derived from the spectra and indicates an interstellar absorption of 0.4 mag, in accord with the observed strength of the interstellar K line. We derive the physical parameters (Teff, Mbol, R, L) of the components, and calculate that the mass of each star is close to 4.0 M⊙. We further show that the hot component has already evolved to a position significantly above the zero-age main sequence (ZAMS), and we propose that the primary is making its first ascent of the red-giant branch. From comparisons with evolutionary tracks, we deduce that the age of the binary (since its arrival at the ZAMS) is in the range While we suspect that the components are sufficiently close for some tidal distortion to occur, the effects are not discernible in our data owing to the rather low orbital inclination. The system shows Si i in emission as a result of irradiation of the primary by the hot secondary, but in the optical spectrum we see little other clear evidence of interaction between the components even though the object has a relatively short period and is a strong X-ray source. On the other hand, Hipparcos photometry suggests the existence of a major non-uniformity of the surface of the primary star.

Study of the high rate performance of the MicroCAT detector

The recently developed micro-pattern detectors (CAT, MIRCOMEGAS, GEM, MicroCAT, etc.) are a very promising enrichment for applications with gaseous x-ray detectors. In order to determine their suitability for imaging measurements using strong x-ray sources, in particular synchrotron light sources, the high rate capability has to be considered carefully. Here, a study of the high rate performance of the MicroCAT detector is presented, focusing on the four major high rate parameters: dead time effects, space charge effects, gas gain stability and rate-induced breakdowns.

The X-ray global view of the Galactic Center region with the ASCA survey

We present the pre iminary results of the hard X-ray global mapping of the Galactic Center region with ASCA. Many point sources and diffuse structures are resolved more clearly than before in the 2–10 keV band. Iron line emission is a so intensely distributed along the Galactic plane. It is interpreted that either high temperature plasma concentrates on the Plane, or the molecular clouds illuminated by externa strong X-ray sources are densely distributed along the Plane, or possibly both mechanisms are important.

MERLIN observations of WR 147 (WN8(h)+B0.5V)

WR147 was first discovered to be a strong radio, X-ray and infra-red emission source by Caillault et al. (1985). It was classified as a WN8 type star with a very large mass loss rate and unusual radio emission (α < 0) for a thermal source. This unusual behaviour was explained by MERLIN (Moran et al. 1989) and VLA (Churchwell et al. 1992) observations in which it was resolved into two components: a ‘thermal’ source associated with the Wolf-Rayet star and a non-thermal component ∼ 600 mas to the north. Churchwell et al. showed that the southern component had the expected spectral index of α ≃ 0.6 for free-free emission from a stellar wind. They also showed that the northern component had a spectral index of α ≃ −0.5 and was therefore a non-thermal source, now thought to be due to a colliding wind region.

Observations of colliding-wind effects at long wavelengths: IR to radio

The supersonic winds of the most luminous stars carry kinetic energy as well as mass. Where such stars are members of binary systems, some of this energy is released in strong shocks which form on both sides of the wind-collision boundary. Originally, the consequent heating of the gas in such systems was predicted to make the stars strong X-ray sources. However, the most conspicuous colliding-wind effects have been observed at longer wavelengths: synchrotron radiation from the shock-accelerated electrons and, most unexpectedly, infrared emission from dust condensing in the shock-compressed gas. Recent developments in observational techniques, especially increased spatial resolution, have led to delineation of these effects, and extensive observing campaigns have given a better idea of their incidence.

X‐Ray and Radio Observations of the Cygnus OB2 Association

Several OB stars in the Cygnus OB2 association are among the strongest stellar X-ray and radio sources in the Galaxy. The radio emission is particularly unusual, displaying a high level of variability and nonthermal behavior. We obtained two ROSAT PSPC observations, a ROSAT HRI observation, and three VLA observations of the association during a 2 yr time span. Our study will focus on four stars, Cyg OB2 No. 5, No. 8A, No. 9, and No. 12. Three of the four (Cyg No. 5, No. 9, and No. 12) were relatively constant in their X-ray emission over the 2 yr time frame. The fourth, Cyg OB2 No. 8A, increased in intensity by ~34%. No short-term (hourly) variability was detected. The observed X-ray characteristics (e.g., luminosity, temperature) are found to be consistent with the X-ray properties of other OB stars. The exception is Cyg OB2 No. 12, whose X-ray characteristics are found to be inconsistent with its spectral classification. Detailed spectral analyses of the PSPC data are presented for two absorption models: (1) ISM (cold absorber) and (2) Wind + ISM (warm absorber). The spectral fits suggest that the X-ray sources are located within the stellar wind, and estimates of the X-ray locations are presented. Adopting the radio-derived mass-loss rates, these X-ray locations are found to be consistent with the shock scenario proposed for OB stars. As expected, the radio emission has continued to be highly variable. Nonthermal characteristics are observed in Cyg OB2 No. 8A and No. 12. One of the most unusual nonthermal radio sources, Cyg OB2 No. 9, was found to be thermal in one of our observations. An observation of Cyg OB2 No. 5 also displayed a thermal radio spectrum. A comparison of the observed and intrinsic X-ray fluxes with the observed radio fluxes suggests that these quantities are anticorrelated; the strongest X-ray source is the weakest radio source. This is contrary to normal expectations for a wind-generated model of X-ray and radio emission. We investigate the long-term temporal behavior of both the X-ray and radio emission by comparing our newly acquired data with the previous X-ray (IPC) and radio data over the past 15 yr. Except for three events observed in Cyg OB2 No. 5, which displayed significant increases in its X-ray emission, the X-ray emission has remained relatively constant with a variability level less than 20% over this time span, whereas the radio emission has stayed highly variable with various levels of nonthermal behavior. We present a model to investigate the case in which the X-ray and radio emission are controlled by stellar wind properties and find that the predicted variability should be comparable in both emission processes. This is not observed. It is very intriguing that every time we observe the radio emission, it is different, whereas the X-ray emission always appears to be constant. If the stellar wind is as variable as suggested by the radio data, we believe it is highly implausible that we just happened to miss all periods of X-ray variability. We also investigate the implications of the observed nonthermal radio spectrum of Cyg OB2 No. 8A. Using the synchrotron emission model of White, we find that this nonthermal radio spectrum predicts a mass-loss rate almost 2 orders of magnitude less than that expected for a thermal radio spectrum. This lower mass-loss rate is consistent with an X-ray source located at the base of the stellar wind, contrary to the basic shock scenario. Since these stars show evidence of changing from thermal to nonthermal radio characteristics, it is difficult to understand how such a large change in mass loss did not produce a significant change in the observed X-rays.

A CORAVEL radial-velocity monitoring of S stars: Symbiotic activity vs. orbital separation. III.

Orbital elements are presented for the Tc-poor S stars HR 363 (= HD 7351) and HD 191226. With an or- bital period of 4592 d (=12.6 y), HR 363 has the longest period known among S stars, and yet it is a strong X-ray source. Its X-ray flux is similar to that of HD 35155, an S star with one of the shortest orbital periods (640 d). This surprising result is put in perspective with other diagnos- tics of binary interaction observed in binary S stars. They reveal that there is no correlation between the level of bi- nary interaction and the orbital period. All these activity diagnostics moreover exhibit a strong time-variability. In the well-documented case of HR 1105, this time-variability appears to be a combination of orbital modulation and secular variation. A stream of gas from the red-giant wind, which is heated when funneled through the inner Lagrangian point, has been proposed as the source of the hard photons (Shcherbakov & Tuominen 1992). Dierent viewing angles of the stream during the orbital cycle ac- count for the orbital modulation, whereas long-term fluc- tuations of the mass-loss rate account for the secular vari- ations. Little dependence to the orbital separation is ex- pected for this kind of activity. If such streams are causing the activity observed in the other binary S stars as well, it would provide a natural explanation for the absence of correlation between orbital periods and activity levels, since the red-giant mass loss rate would be the dominant factor. The existence of such funneled streams is moreover predicted by smooth particle hydrodynamics simulations of mass transfer in detached binary systems.

Operational Limits in Tokamak Machines

Different operational limits of tokamaks are reviewed. The finally limiting processes are hard or soft plasma disruptions or a strong x-ray source. The underlying events are explained as far as the physical causes are known. Treated are the density limit, the low-q-limit, the runaway limit, the β–-limit, and the vertical displacement limit. In addition, the spontaneous MHD-instability and a hollow temperature profile situation are presented. The graphical displays are experimental results from the TEXTOR tokamak.VIII. SUMMARYA number of practical limitations for tokamak operation was briefly discussed. These limits play an important role for the operation of future large tokamak devices. They must be avoided by all means to minimize the risk of technical defects on machine and electrical components. The physical mechanisms involved and the precursors to coming disruptions must be known and should be studied on existing experiments today. Strategies to bring the future machines into a safe state, whenever a known precursor to a tokamak disruption is detected, must be developed. Tokamak plasmas are susceptible to disruptive behaviour in the limiting parameter regimes.

The soft X-ray and extremely ultraviolet filters with negligible pinholes transmittance

It is proposed to fabricate two-layer thin film filters without pinholes transmittance of visible and UV light. We describe the design and performance of these filters. Filter consists of two layers of thin metal films fixed to each side of porous membrane with thorough pores or transmission diffraction grating as support. As examples it was made Al or Rh two-layer thin film filters on metallized porous track membrane supports with the 10 −9–10 −10 level of visible and UV light rejection at transmittance T∼0.1 ÷ 0.01 in the Extreme ultraviolet region. Proposed filter is appropriate in the optical experiments with strong continuous X-ray and Extreme ultraviolet radiation sources such as laser plasma, SR sources and the Sun.

X‐Rays from Superbubbles in the Large Magellanic Cloud. V. The HiiComplex N11

The giant H II complex N11 in the Large Magellanic Cloud contains OB associations at several different stages in their life histories. We have obtained ROSAT PSPC and HRI X-ray observations, Curtis Schmidt CCD images, echelle spectra in H? and [N II] lines, and IUE interstellar absorption line observations of this region. The central bubble of N11 has an X-ray luminosity a factor of only 3-7 brighter than that predicted for an energy-conserving superbubble, making this the first detection of X-ray emission from a superbubble without a strong X-ray excess. The region N11B contains an extremely young OB association analogous to the central association of the Carina Nebula, apparently still embedded in its natal molecular cloud. We find that N11B emits diffuse X-ray emission, probably powered by stellar winds. Finally, we compare the tight cluster HD 32228 in N11 to R136 in 30 Dor. The latter is a strong X-ray source, while the former is not detected, showing that strong X-ray emission from compact objects is not a universal property of such tight clusters.

X-RAY OBSERVATIONS OF NGC 1097 AND NEARBY QUASARS

Observations of three different sized regions centered on the optical jet spiral, NGC 1097 have been made with ROSAT. The PSPC observations show a striking excess of bright and medium flux X-ray sources around this hot spot nucleus, Seyfert 1 galaxy. The brightest of these sources are catalogued quasars which suggests the fainter X-ray sources are predominantly quasars also. If so, of the order of at least 10 and possibly considerably more X-ray quasars appear to be associated with NGC 1097 within a radius of 20′. There is a marked segregation, with bright X-ray sources on the side of the bright optical jets and weak X-ray sources on the side of the fainter optical jets. Some, but not all, of this asymmetry could be accounted for by absorption in the plane of the spiral being tilted towards us on the weak source side. Both optical and X-ray evidence point to strong absorption in the disk of NGC 1097 which reaches far beyond the optical limits. High resolution imaging (HRI) of regions closer to NGC 1097 reveal some fainter pairs and lines of X-ray sources aligned across the nucleus near the cones defined by the optical jets. Filaments and patches of ultraviolet emission (1500–1700A) appear to fill in the region between the strong optical jets in the direction of the bright X-ray quasars, suggesting physical association of the ultraviolet emission with the quasars and the galaxy. Finally, ROSAT SURVEY observations have been examined over a 4 × 4 degree field centered on NGC 1097. A line of X-ray sources going through the galaxy in the direction of the strongest optical jet includes a strong X-ray quasar with its X-ray isophotes extended toward NGC 1097. In approximately the opposite direction, 1.9 degrees distant, is a strong X-ray source (.5cts s-1) which is here identified with a 16.5 mag BL Lac object.

蛋白質構造解析法の最近の進歩

Recent development of crystal structure determination methods enables us to produce ab initio solution for protein crystals. Some such methods are based on reciprocal space direct methods and some of them employs real space density modification methods. One of most successful methods called Shake & Bake is a hybrid of reciprocal and real space methods. This article introduces recently developed methods which have been successfully applied to protein crystals.Although many methods described here require atomic resolution data, it is getting possible to collect high resolution data for standard protein crystals with development of data collection technique at low temperature and strong synchrotron X-ray source such as Spring-8.

Spectra of Two X-Ray–Emitting Quasi-Stellar Objects Apparently Ejected from the Seyfert Galaxy NGC 2639

This Letter presents the results of optical spectrophotometry of two blue stellar objects identified at the centers of two strong, compact X-ray sources located nearly symmetrically on either side of the LINER/Seyfert 2 galaxy NGC 2639 in the direction of its minor axis. The spectra presented here show that both are QSOs with remarkably similar spectra; the redshifts are, for NGC 2639 No. 8, z = 0.3048 ± 0.0012, and for NGC 2639 No. 3, z = 0.3232 ± 0.0004 (the former confirms an earlier identification and redshift measurement by Arp). Their location with respect to NGC 2639, the similarity of their optical spectra and redshifts, and their strong compact X-ray emission suggest that they are associated with NGC 2639, in line with the results of an analysis on ROSAT archival data in which an apparently statistically significant excess of strong compact X-ray sources has been found in the fields of X-ray-emitting Seyfert galaxies.

X-ray and molecular emission from the nearest region of recent star formation.

The isolated, young, sunlike star TW Hya and four other young stars in its vicinity are strong x-ray sources. Their similar x-ray and optical properties indicate that the stars make up a physical association that is on the order of 20 million years old and that lies between about 40 and 60 parsecs (between about 130 and 200 light years) from Earth. TW Hya itself displays circumstellar CO, HCN, CN, and HCO+ emission. These molecules probably orbit the star in a solar-system-sized disk viewed more or less face-on, whereas the star is likely viewed pole-on. Being at least three times closer to Earth than any well-studied region of star formation, the TW Hya Association serves as a test-bed for the study of x-ray emission from young stars and the formation of planetary systems around sunlike stars.

ROSAT Observations of Gamma-Ray Burst Error Boxes. II. GRB910814 and GRB920525

view Abstract Citations References (11) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS ROSAT Observations of Gamma-Ray Burst Error Boxes. II. GRB910814 and GRB920525 Harrison, T. E. ; McNamara, B. J. ; Williams, C. L. ; Wagner, R. M. Abstract We present ROSAT PSPC observations of the southeastern quadrant of the COMPTEL error box of GRB9 10814, and ROSAT HRI observations of the Inter- Planetary Network (IPN) error box of GRB920525. The goal of these observations was to search for a quiescent x-ray counterpart of these gamma-ray bursts. The field of the x-ray observations for GRB910814 included 1.5x of the IPN error annulus within the COMPTEL 2σ error contour. Thirty-nine x-ray sources were detected within the 2^deg^ field of the PSPC observation. One of these sources is located within the IPN annulus, but this detection is consistent with the expected background rate for faint x-ray sources. B and V CCD images of the fields of the nine strongest x-ray sources were obtained to try to identify the optical counterparts of these sources. Likely candidates were identified for a number of these x-ray sources. In the field of GRB920525, four x-ray sources were identified, one of which was bright. None of these sources, however, were located within the IPN error box. Publication: The Astronomical Journal Pub Date: July 1996 DOI: 10.1086/118002 Bibcode: 1996AJ....112..216H Keywords: X-RAYS: BURSTS full text sources ADS | data products SIMBAD (94) NED (49) HEASARC (1)

CGRO/OSSE observations of the Cassiopeia A Supernova remnant

Cassipeia A, the youngest known supernova remnant in the Galaxy and a strong radio and X-ray source, was observed by OSSE 1992 July 16-August 6. Its close distance (approximately 3 kpc) and its young age (approximately 300 yr) make Cas A the best candidate among known supernova remnants for detecting Ti-44 gamma-ray lines. We find no evidence of emission at 67.9 keV, 78.4 keV, or 1.157 MeV, the three strongest Ti-44 decay lines. From simultaneous fits to the three lines our 99% confidence upper limit to the flux in each line is 5.5 x 10(exp -5) gamma/sq cm s. We also report upper limits for the 4.44 MeV C-12 nuclear de-excitation line, which could be produced by interactions of acclerated particles in the supernova remnant, and for the hard X-ray continuum.

ROSAT detection of diffuse hot gas in the edge-on galaxy NGC 4631

ROSAT observation is presented of the edge-on spiral galaxy NGC 4631, a nearby Sc/SBd galaxy best known for its extended radio halo. Because of the low foreground Galactic X-ray-absorbing gas column density, N(sub H) approximately 1.4 x 10(exp 20)cm(exp -2), this observation is sensitive to gas of temperature greater than or equal to a few times 10(exp 5) K. A soft (approximately 0.25 keV) X-ray radiation out to more than 8 kpc above the midplane of the galaxy was detected. The strongest X-ray emission in the halo is above the central disk, a region of about 3 kpc radius which shows high star formation activity. The X-ray emission in the halo is bordered by two extended filaments of radio continuum emission. Diffuse X-ray emission from hot gas in the galaxy's disk was found. The spectrum of the radiation can be characterized by a thermal plasma with a temperature of 3 x 10(exp 6) K and a radiative cooling rate of approximately 8 x 10(exp 39) ergs s(exp -1). This rate is only a few percent of the estimated supernova energy release in the interstellar medium of the galaxy. Analysis of the X-ray spectrum shows evidence for the presence of a cooler (several times 10(exp 5) K) halo gas component that could consume a much larger fraction of the supernova energy. Strong evidence was found for disk/halo interaction. Hot gas apparently blows out from supershells in the galaxy's disk at a rate of approximately 1 solar mass yr(exp -1). This outflow of hot gas drags magnetic field lines up in the halo and forms a magnetized gaseous halo. If the magnetic field lines are still anchored to the disk gas at large disk radii, the outflowing gas may be confined high above the disk by magnetic pressure. A strong X-ray source which coincides spatially with an H I supershell has been identified. However, the source is likely an extremely luminous X-ray binary with L(sub chi)(0.1 - 2 keV) approximately 5 x 10(exp 39) ergs s(exp -1), which makes it a stellar mass black hole candidate.

ROSAT/IUE discovery of a white dwarf companion to HD 33959C (F4V)

We report the discovery, from the ROSAT EUV and X-ray all-sky surveys, and from IUE spectra, of a white dwarf (WD) companion to HD 33959C (= ADS 3824C, F4V, m V = 7.95). RE 0515+324 is among the 10 brightest EUV sources in the sky in the 100-200 A band. It is also a strong soft X-ray source. IUE observations of candidate objects have revealed a previously uncatalogued hot DA WD, visually unresolved from HD 33959C, making the pair one of three or four suggested Sirius-like systems. The estimated EUV luminosity is of the order of 400 times greater than that of Sirius B, implying that the WD is much hotter (cf. T eff = 24 000 K for Sirius B) and probably hydrogen-rich

Small-Angle Scattering of Synchrotron Radiation for Studying Solid State and Biological Systems

Small-angle scattering of X-rays (or neutrons) allows the study of structures with sizes from 1 to 100 nm, and the applications range from biology to materials science. Traditionally, the technique has been applied to stuctural analysis in two very different ways. The first, crystallographic small-angle diffraction, is used to study the periodic arrangement of atoms, molecules, or groups of molecules. In this case one has to interpret sharp Bragg peaks occurring at small scattering angles. This technique, which relates to crystallography, shall not be discussed here. The second way, which is the subject of this paper, consists in the interpretation of the broad, diffuse small-angle scattering containing information on size, shape, and orientation of inhomogeneities (like precipitates, pores, macromolecules in solution, etc.) with sizes ranging from 1 to ≈100 nm. Such kind of information may, in principle, also be obtained by electron microscopy. The advantage of small-angle scattering is the fact that the obtained parameters (size, shape, orientation, etc.) represent average values over macroscopic sample regions, whereas the advantage of electron microscopy is the possibility to image individual objects. Small-angle scattering has been introduced mainly by Guinier [1] and by Kratky and Porod [2]. The principles of the method are reviewed in several textbooks [3-5]. In recent years, the availability of strong X-ray source as well as position-sensitive detectors has increased the potential of the technique and with the use of synchrotron radiation new applications (like, e.g., anomalous scattering, time-resolved studies, three-dimensional reconstruction of anisotropic scattering)

Rapid oscillations in cataclysmic variables. VIII - YY Draconis (=3A 1148 + 719)

A 16th magnitude cataclysmic variable presumably a dwarf nova, was detected near one of the positions permitted for the hard (2-10 keV) X-ray source 3A 1148 + 719. The optical and UV spectra of YY Dra are fairly typical of cataclysmic variables, except that the TiO absorption bands of an M dwarf can be seen for greater than 5000 A. This shows that the accretion disk is intrinsically faint in quiescence, suggesting a very low accretion rate. Yet the fairly blue continuum slope in the vacuum UV indicates the presence of a small hot object, presumably the white dwarf. The radial velocities at H-alpha indicate a 4.0-hr orbital period, and the IR light curve appears to show the expected 'double-humped' waveform from the distorted secondary. High-speed photometry in the U band reveals a stable periodicity of about 1-percent semiamplitude at a period of 275 s, with some power also in the subharmonic at about 550 s.