The use of x-ray scattering to study the anomalous elastic properties of fe-ni alloys
X-ray scattering technique for study of elastic properties of nickel-iron alloy
X-RAY SCATTERING↗
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Spectra of Her X-1 near a turn-on in the 35-day cycle
X-ray spectra for Her X-l are presented for times before, during, and after a turn-on in the 35 day on-off cycle, as well as during an anomalous dip in the X-ray intensity. All four spectra are well represented by a power law of number index approximately .9 with a high energy cutoff near 20 keV. However, the column density of cold matter along the line of sight as estimated by the low energy cutoff varies substantially among the four intervals. The low level flux present prior to turn-on does not pulse and shows very little low energy absorption, in contrast to the X-rays observed during the turn-on and the anomalous dip. It seems likely that the pre-turn-on flux is composed of X-rays scattered into the line of sight by material away from the accretion disk.
Becker, R. H.↗
Spectra of Hercules X-1 near a turn-on in the 35 day cycle
X-ray spectra for Her X-1 are presented for times before, during, and after a turn-on in the 35 day on-off cycle, as well as during an anomalous dip in the X-ray intensity. All four spectra are well represented by a power law of number index 0.9 with a high-energy cutoff near 20 keV. However, the column density of cold matter along the line of sight as estimated by the low-energy cutoff varies substantially among the four intervals. The low level flux present prior to turn-on was not seen to pulse and showed very little low-energy absorption, in contrast to the X-rays observed during the turn-on and the anomalous dip. It seems likely that the pre-turn-on flux is composed of X-rays scattered into the line of sight by material away from the accretion disk. An accurate determination of the pulsation period for Her X-1 during 1975 August finds the period has decreased to 1.2378065 plus or minus 0.0000001 s.
Becker, R. H.↗
Effect of Scattering on Instabilities in Line-driven Stellar Winds
Line driven O-B stellar winds are unstable to perturbations of short spatial wavelength and the growth rates for such instabilities are very rapid. The nature of the nonlinear development of this instability is unknown, but might possibly be one of blobs of gas driven through ambient gas or a quasiregular train of outward moving shocks. In either case the resulting dissipation of mechanical energy might explain the observed anomalous heating n O-B stars as evidenced by their X-ray emission and high ionization state. It also might explain the observed fine structure of the absorption lines and their time variability. The driving due to the absorption of the stellar continuum flux was considered and the effects of the diffuse, scattered radiation field were neglected. It was shown that under certain special conditions the effect of scattering could reduce the instability growth rate to zero. A stability analysis that includes scattering, but that uses the more physically realistic assumption of complete redistribution instead of coherent scattering, and that includes the effects of transverse velocity gradients, which become important as the flow moves away from the stellar surface is presented. It is found that the instability is eliminated right at the base of the wind, but that as the flow moves outward the instability rate rapidly becomes equal to a substantial fraction of the calculated value, the fraction asymptotically reaching 80% at large radii. Since this still implies many e folds in a characteristic outflow time, the primary conclusion that these winds are highly unstable is unchanged.
Owocki, S. P.↗
High-Resolution X-Ray Spectroscopy of the Galactic Supernova Remnant Puppis A with the XMM-Newton RGS
We present high-resolution X-ray spectra of cloud-shock interaction regions in the eastern and northern rims of the Galactic supernova remnant Puppis A, using the Reflection Grating Spectrometer onboard the XMM-Newton satellite. A number of emission lines including K(alpha) triplets of He-like N, O , and Ne are clearly resolved for the first time. Intensity ratios of forbidden to resonance lines in the triplets are found to be higher than predictions by thermal emission models having plausible plasma parameters. The anomalous line ratios cannot be reproduced by effects of resonance scattering, recombination, or inner-shell ionization processes, but could be explained by charge-exchange emission that should arise at interfaces between the cold/warm clouds and the hot plasma. Our observations thus provide observational support for charge-exchange X-ray emission in supernova remnants.
Katsuda, Satoru↗
Chandra X-Ray Observations of the Anomalous X-Ray Pulsar 1E 2259+58.6
We present X-ray imaging, timing, and phase resolved spectroscopy of the anomalous X-ray pulsar 1E 2259+58.6 using the Chandra X-ray Observatory. Time resolved X-ray spectra show no significant variation as a function of pulsar spin phase. The phase averaged spectrum is well described by a powerlaw plus blackbody model; we find no evidence for spectral features. We derive a spin period. We have detected a halo beyond the central source, possibly due to dust scattering in the ISM (interstellar matter).
Patel, Sandeep K.↗
On the Extended Emission of the Anomalous X-ray Pulsar IE 1547.0-5408
We present an analysis of the extended emission around the anomalous X-ray pulsar IE 1547.0-5408 using four XMM-Newton observations taken with the source in varying states of outburst as well as in quiescence. We find that the extended emission flux is highly variable and strongly correlated with the flux of the magnetar. Based on this result, as well as on spectral and energetic considerations, we conclude that the extended emission is dominated by a dust-scattering halo and not a pulsar wind nebula (P-VVN), as has been previously argued. We obtain an upper limit on the 2-10 keV flux of a possible PWN of 4.7 x 10(exp -14) erg/s/sq cm, three times less than the previously claimed value, implying an efficiency for conversion of spin-down energy into nebular luminosity of <9 x 10(exp -4) .
Olausen, S. A.↗
X-Ray Spectral Studies of AGN with the ASCA Satellite
This project involved the interpretation of Advanced Satellite for Cosmology and Astrophysics (ASCA) observations of Active Galactic Nuclei (AGN), with emphasis on four different aspects of the AGN phenomenon: (1) Absorption by hot gas in blazars: This anomalous absorption was detected in several objects, notably the BL Lacertae (BL Lac) object 1426+428. (2) Separation of blazar and Seyfert components in superluminal radio galaxies and quasars: Both components were found in the radio galaxies samples, but with no clear trend in which dominates. (3) Detection of high energy Compton components in blazars: Both BL Lacs and quasars show hard X-ray spectra that represent the onset of the Compton-scattered gamma-ray component. (4) Correlation of X- and gamma-ray emission in blazars: Several multiwavelength monitoring campaigns showed a correlation between X- and gamma-rays in blazars.
Urry, C. Megan↗
Chandra Observations of the Anomalous X-ray Pulsar 4U 0142+61
We present X-ray imaging, timing, and phase resolved spectroscopy of the anomalous X-ray pulsar 4U 0142+61 using the Chandra X-ray Observatory. The spectrum is well described by a power law plus blackbody model with Gamma = 3.35(2), kT=0.458(3) keV, and N-H = 0.91(2) x 10(exp 22)/sq cm); we find no significant evidence for spectral features (0.5 - 7.0 keV). Time resolved X-ray spectroscopy shows evidence for evolution in phase in either Gamma, or kT or some combination thereof as a function of pulse phase. We derive a precise X-ray position for the source and determine its spin period, P=8.68866(30) s. We have detected emission beyond 4 arcsec from the central source and extending beyond 100 arcsec, likely due to dust scattering in the interstellar medium.
Patel, Sandeep K.↗
X-ray spectroscopy of the ultrasoft transient 4U 1543 - 47
The X-ray transient 4U 1543 - 47 was observed in August 1983 by the Exosat observatory near the maximum of an outburst. The X-ray spectrum was measured using a gas scintillation proportional counter (GSPC) and a transmission grating spectrometer (TGS). A broad (FWHM about 2.7 keV) line at 5.9 keV is detected in the GSPC, which is interpreted as a redshifted and broadened iron K-alpha line. The line broadening and redshift may arise from either Compton scattering in a cool plasma with small optical depth and/or from Droppler and relativistic effects in the vicinity of compact object. The spectrum below 2 keV, obtained with the TGS, shows evidence for a broad emission feature at 0.74 keV, which may be an iron L-transition complex. However, such an emission feature could be an artifact caused by an anomalously low interstellar absorption by neutral oxygen. The contimuum emission is extremely soft and is well described by an unsaturated Comptonized spectrum from very cool plasma (kT = 0.84 keV) with large scattering depth.
Van Der Woerd, H.↗
The Nature and Cause of Spectral Variability in LMC X-1
We present the results of a long-term observation campaign of the extragalactic wind-accreting black-hole X-ray binary LMC X-1, using the Proportional Counter Array on the Rossi X-Ray Timing Explorer (RXTE). The observations show that LMC X-1's accretion disk exhibits an anomalous temperature-luminosity relation. We use deep archival RXTE observations to show that large movements across the temperature-luminosity space occupied by the system can take place on time scales as short as half an hour. These changes cannot be adequately explained by perturbations that propagate from the outer disk on a viscous timescale. We propose instead that the apparent disk variations reflect rapid fluctuations within the Compton up-scattering coronal material, which occults the inner parts of the disk. The expected relationship between the observed disk luminosity and apparent disk temperature derived from the variable occultation model is quantitatively shown to be in good agreement with the observations. Two other observations support this picture: an inverse correlation between the flux in the power-law spectral component and the fitted inner disk temperature, and a near-constant total photon flux, suggesting that the inner disk is not ejected when a lower temperature is observed.
Ruhlen, L.↗