Engineering topics

Madejski, G. M.

Publications and source records attributed to Madejski, G. M..

22 records · Page 2

NASA NTRS1992

The X-ray variability of AGN and the anomalous behavior of NGC 6814

The power spectra of the X-ray variable AGN are typically scale invariant with no characteristic timescale. The one strong exception to this is NGC 6814, where the EXOSAT data showed evidence for a periodic component at 12200 +/- 100 seconds. The power spectra of a GINGA lightcurve from this source, found using simulation techniques to account for the uneven sampling, also cannot be well fit by a single power law. A folded light curve analysis of GINGA data shows strong evidence for this periodic component. A second GINGA observation of this source taken one year later is consistent with the phenomena being completely periodic and phase coherent for 7 periods in the range of 12,110-12,145 seconds. Including the (optimistic) limits from the folding selects a period of 12130.39 +/- 0.05 seconds. Phase coherence is not maintained between this and the EXOSAT observations, as the structure of the folded light curves is very different. Thus the periodicity is long lived and stable, but phase coherence is only maintained on timescales of about 1 year.

Done, C.↗

NASA NTRS1991

Einstein Observatory SSS and MPC observations of the complex X-ray spectra of Seyfert galaxies

The X-ray spectra of 25 Seyfert galaxies measured with the Solid State Spectrometer on the Einstein Observatory have been investigated. This new investigation utilizes simultaneous data from the Monitor Proportional Counter, and automatic correction for systematic effects in the Solid State Spectrometer which were previously handled subjectively. It is found that the best-fit single-power-law indices generally agree with those previously reported, but that soft excesses of some form are inferred for about 48 percent of the sources. One possible explanation of the soft excess emission is a blend of soft X-ray lines, centered around 0.8 keV. The implications of these results for accretion disk models are discussed.

Turner, T. J.↗

NASA NTRS1988

High resolution X-ray spectroscopy using microcalorimeters

The use of microcalorimeters for high-resolution, high quantum efficiency, nondispersive X-ray spectroscopy has been demonstrated over the past few years. In this paper, the principles of X-ray calorimetry are reviewed, and the results of ongoing X-ray tests using microcalorimetry are summarized. An approach to building an X-ray calorimeter spectrometer is discussed.

Kelley, R. L.↗

NASA NTRS1983

X-ray studies of BL Lacertae objects with the Einstein Observatory - Confrontation with the synchrotron self-Compton predictions

X-ray flux densities measured with the Einstein Observatory are presented for a set of LB Lac objects with available VLBI angular sizes. The static, single-component synchrotron self-Compton formalism is used to predict the X-ray flux densities. Ratios of 10 to the -6th to the 10 to the -8th are found for the observed to predicted flux densities and it is concluded that such a model, at least in its simplest form, does not explain the X-ray emission from these objects as a class. The hypothesis that the compact source is in relativistic motion allows a simple resolution of the discrepancy. The results agree qualitatively with a broad distribution of bulk Lorentz factors Gamma with a fairly low typical value of Gamma approximately equal to and with a quasi-isotropic distribution of the direction of ejection relative to our line of sight.

Madejski, G. M.↗