K. Koyama

The X-ray spectra of high-luminosity active galactic nuclei observed by Ginga

Results are presented on the X-ray emission from 13 objects, observed by Ginga as part of a spectral survey of bright quasars in the energy range 2-20 keV. The distribution of the power-law energy index for this sample has a mean of 0.81 and shows significant intrinsic dispersion, σ = 0.31, values which are broadly compatible with those from samples of lower luminosity active galactic nuclei. The mean spectral slope is clearly too sleep to fit the spectrum of the cosmic diffuse X-ray background (CXB) at energies less than 20 keV, confirming the spectral paradox in the discrete-source explanation of the CXB

X-ray spectrum from gamma Cassiopeiae

The X-ray source gamma Cassiopeiae was observed with the X-ray astronomy satellite Tenma. A strong iron line was observed at 6.8 keV with an intensity of 280 eV equivalent width as is expected from a highly ionized plasma. The strength of the iron line at 6.8 keV and the existence of a thin thermal plasma are in conflict with models that require a neutron star as the X-ray source. From many of the X-ray binaries with a neutron star, only a weak ionized iron line (less than 50 eV at 6.7 keV) or strong reprocessed iron line (6.4 keV) has been observed with Tenma. This Letter suggests the possible existence of a degenerate dwarf as a companion for gamma Cas instead of a neutron star. The lack of luminosity from the white dwarf companion is attributed to a nonspherical mass loss from the primary. 23 references.

Spectra and pulse period of the binary X-ray pulsar 4U 1538-52

The 530 s binary X-ray pulsar 4U 1538-52 was observed from the X-ray astronomy satellite Tenma in 1983 June-July. An improved orbital ephemeris was derived. Also, high-quality X-ray spectra were obtained by taking into account the contribution of the Galactic ridge emission. It was found that the iron K-line emission from this source is weak, contrary to previous reports. The observed pulsation period, about 529.8 s, is about 0.4 s longer than that measured in 1976-1977, implying an average spin-down rate of 3.8 x 10 to the -9th s/s. In addition, there is some evidence for a much larger rate of instantaneous period increase. These results suggest that 4U 1538-52 is a wind-fed pulsar, and its pulsation period changes in a random-walk manner in response to fluctuations in the external torque. This is very similar to the case of Vela X-1. 46 references.

Simultaneous Multifrequency Observations of the BL Lacertae Object Markarian 421

Simultaneous multifrequency observations of the BL Lac object Mrk 421 covering radio through X-ray wavelengths were performed on two occasions separated by 5 weeks in January and March 1984, and each observation was coordinated for about 1 week. Composite multifrequency spectra of the central nonthermal component were obtained at the two epochs after subtracting the optical and infrared light of the underlying galaxy. The spectra show the gradual steepening toward high frequency; the power law indices are about 0.1, about 0.6, and about 1.0 for radio, infrared-optical, and UV bands, respectively. The UV and optical-infrared fluxes decreased by about 20 percent in 5 weeks, while the radio flux remained stable. The X-ray flux decreased by a factor of about 2, and the change was more pronounced at hard X-rays, which suggest that X-ray emission possibly consists of two components. The degree of polarization at the optical band varied on the time scale of a few days, while the position angle remained unchanged. Physical parameters of Mrk 421 are discussed in terms of the synchrotron self-Compton model. 55 references.

GINGA observations of three X-ray-luminous early-type galaxies : NGC 4472, NGC 4636, and NGC 3998

Observations of three X-ray luminous early-type galaxies, NGC 4472, NGC 4636 and NGC 3998, with the satellite Ginga, are presented. The X-ray spectra of NGC 4472 and NGC 4636 can be described as thermal emission from an optically thin plasma. The temperatures of the hot gas are determined. The X-ray spectrum of NGC 3998 is well fitted by a power-law model having a photon index of 2.0, the same sort of spectrum typical of AGN.

Delays of Optical Bursts in Simultaneous Optical and X-Ray Observations of MXB 1636-53

Observations of simultaneous optical and X-ray bursts from 4U/MXB 1636-53 were made using the Hakucho burst monitor system and optical telescopes at the European Southern Observatory during 1979 and 1980. The six best cases among the 10 coinciding observations are analyzed in terms of a model in which the optical emission is the result of reprocessing of X-rays (through blackbody heating). From this analysis, the temperature (spatially averaged) and size of a reprocessor, and the smearing and delay of the optical bursts are obtained. For the maximum temperatures of the optical reprocessor, the values differ from burst to burst, ranging from about 3 x 10 to the 4th to about 10 to the 5th K. The present analysis suggests that the size of the reprocessor varies by a factor of a few. For the smearing of the optical bursts an upper limit of a few seconds is derived. The most important result of this analysis is that the delay times are not the same for all bursts. The possible constraints which these results put on a low-mass binary model of this burst source are discussed.

Discovery of 111 second pulsation from the X-ray source Scutum X-1

A 111-sec-period X-ray pulsation from Sct X-1 is reported. The pulse profile was found to exhibit double peaks. The x-ray spectrum of Sct X-1 is fitted by a single power-law function with a photon index of about 1.9. Evidence for extremely large absorption (greater than 10 to the 23rd H/sq cm) has been found in the low-energy band and near the iron K-edge. When combined with the previous observations, these data show that the X-ray flux has been variable over more than two orders of magnitude. 15 refs.

Morphological assessment of chronic total occlusions by combined coronary computed tomographic angiography and intravascular ultrasound imaging

Aims The relationship between CTO morphology and vessel remodelling is unclear. We described chronic total occlusion (CTO) morphology using coronary computed tomographic angiography (CCTA) combined with intravascular ultrasound (IVUS). Methods and results Pre‐intervention CCTA and IVUS of 130 CTO lesions (128 patients) were evaluated. Based on CCTA, positive CTO lesion remodelling [PR, maximum CTO segment vessel diameter > proximal reference vessel diameter (RVD)] was seen in 44 (33.8%) lesions. In the other 86 lesions without PR, 74 (56.9%) had a minimum CTO segment vessel diameter >50% of the proximal RVD and were classified as non‐PR; 12 (9.2%) lesions had a minimum CTO segment vessel diameter ≤50% of the proximal RVD and were classified as collapse. Comparing the three groups, CTO with PR had the greatest maximum atheroma cross‐sectional area (CSA) while the collapse group had the least atheroma CSA (16.0 mm2 [12.0, 19.4] vs. 9.1 mm2 [6.0, 15.9], P < 0.001). The maximum arc of attenuated plaque was greatest in the PR group (51° [0, 167]); and the maximum arc of calcium was greatest in the non‐PR group (91° [51, 174]). In the collapse group distal to the occluded segment, there was a normal‐appearing vessel by IVUS that corresponded to the collapsed segment by CCTA; its minimum plaque burden was 33.2% [19.9, 38.1] with a smooth concave‐shaped lumen surface, implying that the CCTA collapse segment was not occluded. Conclusion Not all CTOs are the same with regard to lesion remodelling and underlying morphology. The combination of IVUS and CCTA can help to categorize CTO morphology.

A prospective, single-center, randomized study to assess whether automated coregistration of optical coherence tomography with angiography can reduce geographic miss

We sought to evaluate whether automated coregistration of optical coherence tomography (OCT) with angiography reduces geographic miss (GM) during coronary stenting.

Effect of orbital atherectomy in calcified coronary artery lesions as assessed by optical coherence tomography

We sought to assess plaque modification and stent expansion following orbital atherectomy (OA) for calcified lesions using optical coherence tomography (OCT).