Long term variability of Cygnus X–1 Pottschmidt, K.; Wilms, J.; Nowak, M. A. ...
Astronomy and astrophysics (Berlin),
09/2003, Letnik:
407, Številka:
3
Journal Article
We study the long term evolution of the relationship between the root mean square (rms) variability and flux (the "rms-flux relation") for the black hole Cygnus X-1 as monitored from 1996 to 2003 ...with the Rossi X-ray Timing Explorer (RXTE). We confirm earlier results by Uttley & McHardy (2001) of a linear relationship between rms and flux in the hard state on time scales >5 s reflecting in its slope the fractional rms variability. We demonstrate the perpetuation of the linear rms-flux relation in the soft and the intermediate state. The existence of a non-zero intercept in the linear rms-flux relation argues for two lightcurve components, for example, one variable and one non-variable component, or a possible constant rms component. The relationship between these two hypothesized components can be described by a fundamental dependence of slope and intercept at time scales 10 ksec with long term averages of the flux.
Long time scale radio-X-ray correlations in black holes during the hard state have been found in many sources and there seems to emerge a universal underlying relationship which quantitatively ...describes this behavior. Although it would appear only natural to detect short term emission patterns in the X-ray and - with a certain time lag - in the radio, there has been little evidence for this up to now. The most prominent source for radio-X-ray correlations on short time scales (minutes) so far remains GRS 1915+105 where a single mass ejection could be detected successively in X-ray, IR, and radio wavebands. We analyze a database of more than 4 years of simultaneous radio-X-ray data for Cygnus X-1 from the Ryle Telescope and RXTE PCA/HEXTE. We confirm the existence of a radio-X-ray correlation on long time scales, especially at hard energies. We show that apparent correlations on short time scales in the lightcurves of Cygnus X-1 are most likely the coincidental outcome of white noise statistics. Interpreting this result as a breakdown of radio-X-ray correlations on shorter time scales, this sets a limit to the speed of the jet.
INTEGRAL-RXTE observations of Cygnus X-1 Pottschmidt, K.; Wilms, J.; Chernyakova, M. ...
Astronomy and astrophysics (Berlin),
11/2003, Letnik:
411, Številka:
1
Journal Article
Recenzirano
Odprti dostop
We present first results from contemporaneous observations of Cygnus X-1 with INTEGRAL and RXTE, made during INTEGRAL's performance verification phase in 2002 November and December. Consistent with ...earlier results, the $3{-}250$ keV data are well described by Comptonization spectra from a Compton corona with a temperature of $kT\sim50{-}90$ keV and an optical depth of $\tau\sim 1.0{-}1.3$ plus reflection from a cold or mildly ionized slab with a covering factor of $\Omega/2\pi\sim 0.2{-}0.3$. A soft excess below 10 keV, interpreted as emission from the accretion disk, is seen to decrease during the 1.5 months spanned by our observations. Our results indicate a remarkable consistency among the independently calibrated detectors, with the remaining issues being mainly related to the flux calibration of INTEGRAL.
This paper reports on a silicon angular rate sensor designed for automotive applications like overroll protection and electronic skidding protection. The sensor is based on a tuning fork principle ...with the tines being piezoelectrically excitated perpendicular to the wafer surface. Due to the Coriolis effect, an angular rate parallel to the axis of the stem generates a periodic torque, which results in a torsional oscillation of the stem. This torsional oscillation is detected with an implanted piezoresistor located in the middle of the stem. A slot in the center of the stem enhances the shear stress at the read-out piezoresistor position resulting in a higher sensitivity. The latest sensor design with a split electrode allows an electronic compensation of mechanical imbalance in order to reduce the sensor offset and offset drift. Additionally, this electrode configuration can generate a periodic torque to perform a permanent test of the sensor functioning and the sensitivity during operation.
A main problem for the applicability of silica aerogels as thermal insulation materials at temperatures above 600°C is viscous sintering, which may lead to a significant density increase with time. ...Modification of silica aerogels via integration of alumina yields aerogels with increased stability against sintering. The onset of sintering of alumina silica aerogels occurs at about 900°C compared with about 600°C for pure silica aerogels. The sintering process was investigated as a function of alumina content, density and particle size. Alumina-modified silica aerogels were studied by dilatometry, viscosimetry and thermogravimetry during non-isothermal and isothermal heat treatment.
Long term variability of Cyg X-1 Gleissner, T.; Wilms, J.; Pottschmidt, K. ...
Astronomy and astrophysics (Berlin),
02/2004, Letnik:
414, Številka:
3
Journal Article
Recenzirano
Odprti dostop
We study the long term evolution of the relationship between the root mean square (rms) variability and flux (the “rms-flux relation”) for the black hole Cygnus X-1 as monitored from 1996 to 2003 ...with the Rossi X-ray Timing Explorer (RXTE). We confirm earlier results by CITE of a linear relationship between rms and flux in the hard state on time scales >5 s reflecting in its slope the fractional rms variability. We demonstrate the perpetuation of the linear rms-flux relation in the soft and the intermediate state. The existence of a non-zero intercept in the linear rms-flux relation argues for two lightcurve components, for example, one variable and one non-variable component, or a possible constant rms component. The relationship between these two hypothesized components can be described by a fundamental dependence of slope and intercept at time scales $\la$10 ksec with long term averages of the flux.
Long term variability of Cygnus X-1 Gleissner, T.; Wilms, J.; Pooley, G. G. ...
Astronomy and astrophysics (Berlin),
10/2004, Letnik:
425, Številka:
3
Journal Article
Recenzirano
Odprti dostop
Long time scale radio–X-ray correlations in black holes during the hard state have been found in many sources and there seems to emerge a universal underlying relationship which quantitatively ...describes this behavior. Although it would appear only natural to detect short term emission patterns in the X-ray and – with a certain time lag – in the radio, there has been little evidence for this up to now. The most prominent source for radio–X-ray correlations on short time scales (minutes) so far remains GRS 1915+105 where a single mass ejection could be detected successively in X-ray, IR, and radio wavebands. We analyze a database of more than 4 years of simultaneous radio–X-ray data for Cygnus X-1 from the Ryle Telescope and RXTE PCA/HEXTE. We confirm the existence of a radio–X-ray correlation on long time scales, especially at hard energies. We show that apparent correlations on short time scales in the lightcurves of Cygnus X-1 are most likely the coincidental outcome of white noise statistics. Interpreting this result as a breakdown of radio–X-ray correlations on shorter time scales, this sets a limit to the speed of the jet.
Long term variability of Cygnus X–1 Pottschmidt, K.; Wilms, J.; Nowak, M. A. ...
Astronomy and astrophysics (Berlin),
09/2003, Letnik:
407, Številka:
3
Journal Article
Recenzirano
Odprti dostop
We present the long term evolution of the timing properties of the black hole candidate Cygnus X–1 in the 0.002–128 Hz frequency range as monitored from 1998 to 2001 with the Rossi X-ray Timing ...Explorer (RXTE). For most of this period the source was in its hard state. The power spectral density (PSD) is well modeled as the sum of four Lorentzians, which describe distinct broad noise components. Before 1998 July, Cyg X–1 was in a “quiet” hard state characterized primarily by the first three of these broad Lorentzians being dominant. Around 1998 May, this behavior changed: the total fractional rms amplitude decreased, the peak frequencies of the Lorentzians increased, the average time lag slightly increased, and the X-ray spectrum softened. The change in the timing parameters is mainly due to a strong decrease in the amplitude of the third Lorentzian. Since this event, an unusually large number of X-ray flares have been observed, which we classify as “failed state transitions”. During these failed state transitions, the X-ray power spectrum changes to that of the intermediate state. Modeling this PSD with the four Lorentzians, we find that the first Lorentzian component is suppressed relative to the second and third Lorentzian during the state transitions. We also confirm our previous conclusion that the frequency-dependent time lags increase significantly in the 3.2–10 Hz band during these transitions. We confirm the interpretation of the flares as failed state transitions with observations from the 2001 January and 2001 October soft states. Both the behavior of the PSD and the X-ray lag suggest that some or all of the Lorentzian components are associated with the accretion disk corona responsible for the hard state spectrum. We discuss the physical interpretation of our results.
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