X-ray Intensity Variations Research Articles

ITAL]Rossi X-Ray Timing Explorer[/ITAL] Observations of GRS 1915+105

The Galactic superluminal motion source GRS 1915+105 was observed with the Rossi X-Ray Timing Explorer satellite at several occasions during its ongoing active state. The observed X-ray intensity changes drastically on a variety of timescales ranging from subseconds to days. In particular, the source exhibits quasi-periodic brightness sputters with varying duration and repetition timescale. These episodes occur occasionally, while the more common X-ray intensity variations are faster with much smaller amplitudes. The spectrum during the brightness sputters is remarkably different from the spectrum of the mean high-state emission. We argue that such sputtering episodes are possibly caused by a major accretion disk instability. Based on the coincidence in time of two radio flares following the observed X-ray sputtering episodes, we speculate that superluminal ejections (as observed from GRS 1915+105 during earlier activity periods) are related to episodes of large-amplitude X-ray variations.

Irradiation experiments on high temperature superconductor thin films

Thin single crystalline REBaCuO films (RE = rare earth) grown in different orientations ([100], [001], [110]) were irradiated with 300 keV H + and He + ions at room temperature. Investigations of the ion-induced changes of the transport and especially of the structural properties were performed. The superconducting properties degrade and the unit cell expands under H + and He + irradiations. The loss of superconductivity is not directly connected with an orthorhombic to tetragonal phase transformation for proton irradiated films as in oxygen deficient samples. In a-axis grown films irradiated with protons we observed the formation of a new √2 a c × √2 a c × 3 a c ( a c ∼ 3.8 rA) superstructure induced by oxygen reordering in the basal plane of the unit cell. This is thought to be strongly correlated with the observed metal-insulator transition due to carrier concentration reduction in the CuO 2 planes. Distinct X-ray intensity variations indicate atomic displacements in the cationic sublattices. At higher fluences (i.e. 0.02 dpa) an amorphization process sets in, probably driven by strain in the irradiated films.

Application of Line Modified-Asymmetric Crystal Topography for Qualitative and Quantitative Evaluation of Integrated Circuits

Abstract X-ray diffraction topography is the name given to several x-ray diffraction techniques where large area x-ray beams diffracted from a crystal provide detailed information about the surface structure and internal perfection of crystal microstructures. Since x-ray topographic techniques are based on Bragg (reflection) or Laue (transmission) diffraction from a crystal lattice, they are extremely sensitive to any atomic lattice imperfections and strains. Alterations of the interplanar spacing as small as one part in ten thousand extending over a reasonable number of atomic ce11 lengths can be recorded as a corresponding change in the diffracted beam intensity. Line Modified-Asymmetric Crystal Topography (LM-ACT) is one such reflection technique that shows particular promise in Che field of microelectronics. The LM-ACT system is designed with low angular divergence in the x-ray beam probe. Low probe beam divergence allows details of device geometries on the order of microns to be resolved in the recorded x-ray intensity variation of the diffracted beam. The LM-ACT system was applied here to the study of integrated circuits (IC) after specific processing steps were accomplished during IC fabrication and in the final product condition. Topographs obtained from specular crystal surfaces that were implanted through a patterned mask showed contrast variations between the implanted and non-implanted regions; details of the mask patterns have been resolved on the order of a few microns. LMACT topographs from annealed, and unannealed, Implanted specimens showed marked differences and as a result it is suggested that LM-ACT would be beneficial in optimizing the processing schedule for a particular wafer/electronic system. A significant feature of the LM-ACT technique is the capability for producing high resolution stereo-pair topographs that provide quantitative information through the depth of individual process layers in an integrated circuit.

300 keV proton irradiation effects on structural properties of thin RE 1Ba 2Cu 3O 7− δ films

We report the effects of 300 keV proton irradiations on the structural properties of thin RE 1Ba 2Cu 3O 7− δ films (RE = rare earth) grown in different orientations ([100], [001], [110]). The effects are studied by X-ray and electron diffraction measurements. All three lattice parameters of the orthorhombic structure increase under irradiation and the loss of superconductivity is not directly connected with an orthorhombic to tetragonal phase transition. The irradiation leads to the formation of a new √2 a c×√2 a c×3a c ( a c ≈3.8 A ̊ ) superstructure which forms by an oxygen reordering in the basal plane of the unit cell without oxygen loss. This is thought to be strongly correlated with the observed metal-insulator transition due to a carrier concentration reduction in the CuO 2-planes. Distinct X-ray intensity variations indicate atomic displacements in the cationic sublattices.

Changes in the 11 minute period of 4U 1820 - 30

Observations made in February and April 1989 with the Ginga satellite show that the times of maximum light for the 685 s X-ray intensity variations of 4U 1820 {minus} 30 occur 71 + or {minus} 21 and 94 + or {minus} 21 s earlier than would be expected for the constant-period ephemeris based on previous observations. The times of maximum light observed between 1976 and 1989 are consistent with a constant rate period decrease of 0.074 + or {minus} 0.013 ms/yr. The decrease is found to be significant at the 99.9 percent level. If this reflected a true change in the orbital period, this result would be inconsistent with the standard model in which the 685 s period is that of the orbit of a binary star consisting of a neutron star whose companion is a low-mass (0.07 solar mass) degenerate helium star, and mass transfer is driven by loss of orbital angular momentum through gravitational radiation. The apparent period change may be explained in two ways: either the standard model is incorrect, or 4U 1820 {minus} 30 is being accelerated toward the earth by the gravitational field of another body. Acceleration of the binary by a distant third companionmore » in a hierarchical triple, or by the cluster potential, are both possibilities. 44 refs.« less

Is the 35 day cycle of her x-1 caused by the free precession of the neutron star?

It has been suggested that the 35 day clock mechanism of Her X-1 is caused by the precession of the neutron star. We made calculations for this model. Comparing our calculated results with observations we find: 1. (1) The theoretical light curve over the the 35 day cycle does not agree with the observed curve by Jones and Forman (1976). 2. (2) The change of pulse width and intensity with the 35 day phase is large in the model, seemingly disagreeing with the observations (e.g., Gruber et al. 1980). 3. (3) Parmer et al. (1985) reported that they did not see the expected 35 day variation in X-ray intensity expected in the model. Pravdo et al. (1977) suggested that the observed X-ray pulses were formed by Thomson scattering of symmetric radiating beams generated near the surface of the neutron star. Our analysis based on the theory of Thomson scattering in strong magnetic fields shows that this model agrees well with the observations.

Calorimetric study of the smectic-Ad-smectic-A2 critical point.

High-resolution heat-capacity measurements are reported for the vicinity of the smectic-${A}_{d}$--smectic-${A}_{2}$ critical point in mixtures of undecyloxyphenyl-cyanobenzyloxy benzoate (11OPCBOB) and nonyloxybiphenyl cyanobenzoate (9OBCB). This type of critical point, which has similarities to the familiar liquid-gas (Ising) critical point, is predicted to belong to a new universality class. The variation of ${C}_{\mathrm{px}}$ in two near-critical mixtures with 11OPCBOB mole fractions X=0.655 and 0.641 can be characterized by the critical exponent \ensuremath{\gamma}/\ensuremath{\Delta}=0.6\ifmmode\pm\else\textpm\fi{}0.2. Previously reported smectic layer thicknesses d(T) for a mixture with X=0.642 vary like ${t}^{1\mathrm{\ensuremath{-}}(\ensuremath{\gamma}/\ensuremath{\Delta})}$ with \ensuremath{\gamma}/\ensuremath{\Delta}=0.62. Extensive rounding of the ${C}_{\mathrm{px}}$(T) peak near ${T}_{c}$, which complicates the critical exponent determination, appears to be an intrinsic effect that may be associated with the unusual x-ray intensity variation near ${T}_{c}$.

Binary phase correlated X-ray intensity variations and flaring activity in the RS CVn binary HR 1099

A study of X-ray variability of the RS CVn binary HR 1099 has been carried out using observations made with the monitor proportional counter (MPC) and the imaging proportional counter (IPC) on board the Einstein Observatory. This star, with a total exposure of 8×104s, was observed once simultaneously with the MPC and the IPC covering all binary phases and with the MPC at three other times at different binary phases. Evidence is found for the variation of the X-ray intensity with the 2.837 day period of the binary. The extent of the correlated variations is ∼30 per cent in the IPC and ∼100 per cent in the MPC. The phase of the X-ray maximum coincides with that of the minimum of the optical wave and the X-ray minimum occurs close to the optical wave maximum reported by Bartolini et al. at the epoch 1979.11, which is close to the epoch of the X-ray observations. An intense X-ray flare, having rise time of |$\geqslant 16$| min, decay time of 76min, and total 2−10 keV X-ray energy release of |$\approx5\times10^{34}$| erg, was detected on 1980 February 17. The X-ray spectrum near the flare peak was hard and is best described by a thermal spectrum with |$kT=11.3^{+2.6}_{-1.8}\enspace\text {keV}$| compared to a quiescent state value of 2.0±0.4 keV. A second but less intense flare having decay time of > 33 min was detected on 1979 January 31. The binary phase correlated variations are explained in terms of the star spot model. From the measured values of the X-ray flare parameters and using the coronal loop model, it is concluded that the flare heated plasma cools either mainly by radiation or equally by conduction and radiation.

X-ray intensity and spectral variations in the BL Lac sources H2155-304 and PKS0548-322

The results from the X-ray observations of two BL Lacertae objects, H2155-304 and PKS0548-322, are presented. The observations were carried out with the HEAO-1 A2 Low Energy Detectors, the High Resolution Imager, and the Monitor Proportional Counter aboard the Einstein Observatory. Correlated X-ray intensity variations of about 20 percent in the 0.15-3.5 keV energy band and about 40 percent in the 1.5-10 keV energy band are observed in H2155-304 over a period of about 8 hr. A factor of two change in the intensity of PKS0548-322 in the 3.5-10 keV energy interval is also detected over a time interval of 1 hr. Variations in the X-ray intensity over a timescale of months and the hardening of the spectrum with increasing intensity are seen in the HEAO-1 A2 data on H2155-304. The shortest observed timescale for the variability is used to derive an upper limit on the mass of the central accreting source in the two BL Lac objects studied here.

An XRPD Investigation of a Face-Centered Cubic Metallic Plating

AbstractInternal elastic strain (i.e., residual stress) and the diffracted X-ray intensity variation over several orientations of crystallites with respect to the specimen surface were investigated as a means of differentiating two qualities of polycrystalline nickel plating. A unique instrument based upon a position-sensitive scintillation X-ray detector was used to apply all of the techniques commonly applied to X-ray stress analysis in this investigation. It was concluded that residual stress measurements did not provide a clear distinction between the two specimens, but comparison of the relative intensities diffracted from crystallographic planes at certain orientations with the surface did provide a distinction.

X-ray intensity variations in BL Lac sources H2155-304 and PKS 0548-322

The X-ray Observations of two BL Lac Objects H2155-304 and PKS 0548-322 made with HRI and MPC on the Einstein Observatory show intensity variations on time scale of hours in both the sources. X-ray spectra of the two BL Lacs are derived. Limits on the mass of the accreting compact objects are obtained from time scale and magnitude of variations. Implications of the results are briefly discussed.

Soft X-ray observations of two BL Lacertae objects - Markarian 421 and 501

view Abstract Citations (8) References (22) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Soft X-ray observations of two BL Lacertae objects : Markarian 421 and 501. Singh, K. P. ; Garmire, G. P. Abstract This paper reports on the soft X-ray (0.15-2.8 keV) observations of two BL Lacertae-type objects, viz., Mrk 421 and Mrk 501. The observations were made with the low-energy detectors on the HEAO 1 satellite during the period 1977 August-1978 December. Steep, soft X-ray power-law spectra with photon index Gamma = 3 are found for both Mrk 421 and Mrk 501. The power-law models are found to give a significantly better fit than the thermal models to the observed pulse-height spectra of Mrk 421 and Mrk 501. Day-to-day soft X-ray (0.25 keV band) intensity variations are observed only in Mrk 501. No significant change is found in Gamma from both the BL Lac objects during the period of observations. However, the sum of all the X-ray observations from 1976 until 1980 can be understood in terms of two spectral components of variable intensity to account for the X-ray emission observed between 0.15 and 20 keV from Mrk 421 and Mrk 501. Publication: The Astrophysical Journal Pub Date: October 1985 DOI: 10.1086/163516 Bibcode: 1985ApJ...297..199S Keywords: Bl Lacertae Objects; Emission Spectra; X Ray Sources; Bremsstrahlung; Synchrotron Radiation; Astrophysics full text sources ADS | data products SIMBAD (2) NED (2)

A STATE ANALYSIS METHOD OF TRANSITION-METAL ELEMENTS BY AN ELECTRON PROBE MICROANALYZER

Abstract It was shown that the chemical state of nickel or cobalt could be identified by the state analysis method utilizing the 9th-order Kα1 line. Probable factors of the X-ray intensity variation with chemical state were the self-absorption, the L2L3M4,5 Coster–Kronig process, and the pseudo Lβ emission.

An extended X-ray low state from Hercules X-1

Hercules X-1 exhibits a 35-day cycle in its X-ray intensity1,2 in addition to its pulsar rotational and orbital periodicities of 1.24 s and 1.7 days respectively. The effects of X-ray heating on the companion are visible throughout the 35-day cycle3, suggesting that the observed intensity modulation is caused by periodic blocking of the line of sight to the pulsar. We report here observations made with the EXOSAT Observatory between 1983 June and August that failed to detect the expected 35-day variation in X-ray intensity, although low-level extended X-ray emission was seen. Models where the obscuring of the pulsar is caused by a processing tilted accretion disk have been proposed4–9, although the physics of the tilted disk are not clear10. Alternatively, wave-like thickenings of the accretion disk have been proposed11 to account for the observed modulation. Our EXOSAT observations suggest that a temporary change in the disk structure may have occurred such that the disk was in the line of sight throughout.

Hard X-ray astronomy from balloons

Abstract The region of the electromagnetic spectrum between 15 keV and 300 keV is the first high energy photon band available to the astronomer at balloon altitudes. It also represents the point at which a change in experimental technique is required since grazing incidence X-ray mirrors, and, apart from the use of xenon, gas proportional counters become impracticable Thin, actively shielded sodium iodide detectors form the mainstream X-ray detection units. Directionality is achieved by means of honeycomb and modulation collimators. However as suitable position sensitive planes are developed it is possible to anticipate the increasing usage of the coded aperture mask as the key element for fine angular imaging. Balloon-borne hard X-ray telescopes tend to deploy larger sensitive areas than their satellite cousins, and for this reason, with suitably fast timing of the data, may be used to study the classes of objects which exhibit rapid temporal X-ray intensity variations. Spectral studies are also of great astrophysical importance in this range. Apart from the interest in neutron star line emissions, observations in the soft X-ray region have invariably left doubts as to the true nature of the local production mechanisms for specific objects, this is due to the lack of precise definition of the spectral shape of the emissions, particularly at higher photon energies experimental techniques. The usage of balloons and related astrophysical problems are reviewed.

Dependence of x-ray intensity scaling on target atomic number in laser produced plasmas

We have measured the x-ray emission intensity from plasmas created from a number of targets with atomic number (Z) in the range 6≤Z≤73 using a 1-GW, 5-ns neodymium glass laser. The variation of x-ray intensity with laser intensity (Φ) was observed to depend on the target atomic number and showed a scaling of Φα where α varies from 1.9 to 2.8 for different elements. The observed scalings were found to be consistent with a self-regulating model for plasma heating.

X-ray observations of SS 433 with the Einstein observatory

In this paper I shall discuss observations made of SS 433 in a collaborati study with F.Seward, J.Grindlay and W.Gilmore. The purpose of the study was t investigate the X-ray emitting properties of this object and to search for correlated X-ray and radio intensity variations. The observations were made with the Einstein Observatory, using the High Resolution Ima~er (HRI), the Imaging Proportional Counter (IPC), and the Monitor Proportional Counter (MFC

The variation of pionic X-ray intensity with atomic number

Pionic X-ray intensities have been measured for 57 elemental targets. For each transition, in addition to the broad maximum as a function of Z expected from the Auger effect and the strong absorption, local intensity maxima are observed near Z values of closed atomic shells.

Reciprocity-Law Failure in Radiographic Image-Forming Systems

The Reciprocity-law failure characteristics of three brands of medical blue-sensitive X-ray films exposed with intensifying screens are studied. The variation in X-ray intensity for different points on a reciprocity failure curve is obtained by varying the focus-film distance (FFD), since it is confirmed that the X-ray intensity varies approximately as FFD to the minus 2.15th power, for FFDs from 0.40 to 5.68 meters. All of the films investigated show no high-intensity reciprocity failure effects for exposure times of 1/120 to 5 seconds. However, they show remarkably low-intensity reciprocity failure effects for exposure time longer than about 0.3 sec. It is considered that the existence of this low-intensity reciprocity failure must be taken into consideration, since it would affect the patient dose significantly according to the selection of the exposure conditions.

Anti-correlated hard and soft X-ray intensity variations of the black-hole candidates Cyg X-1 and A0620—00

EXTENDED spectral measurements are now available at more than one time epoch for the powerful Monoceros transient, A0620–00, discovered by Elvis et al.1, and the binary source Cyg X-l. We here point out a basic similarity in the unusual spectral time variations of these sources. Both are black-hole candidates, Cyg X-l by virtue of its orbital dynamics and A0620–00 as suggested by arguments based on the Eddington limit1 and distance estimates of the optical counterpart. Thus the X-ray emission mechanism could be common.