Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userX-ray Variability of Cygnus X-1 In Its Soft State
541
0
0.0
(
0
)
Authors
W. Cui
Ask ChatGPT about the research
No Arabic abstract
We reported previously that for Cyg X-1 there is a settling period following the transition from hard to soft state (astro-ph/9610071). During the transiton, The low energy spectrum (below ~10 keV) varies significantly from observation to observation while the high energy portion changes little. The source reaches nominal soft-state brightness during the settling period. It can be characterized by a soft low-energy spectrum and significant low-frequency 1/f noise and white noise on the power density spectrum (PDS). The low-energy spectrum becomes even softer, and the PDS is completely dominated by the 1/f noise, when the ``true soft state is reached. In this paper, subsequent RXTE observations of Cyg X-1 in the soft state are examined, and the results confirm our earlier conclusions. Furthermore, we show the results from observations taken during a soft-to-hard transition. As expected, the white noise appears again, and accordingly, the 1/f noise becomes less dominant, similar to the settling period at the end of the hard-to-soft transition. The low-frequency 1/f noise has not been observed when Cyg X-1 is in the hard state. Therefore, it seems to be positively correlated with the disk mass accretion rate which is low in the hard state and high in the soft state. The difference in the observed spectral and timing properties between the hard and soft states is qualitatively consistent with a simple ``fluctuating corona model (astro-ph/9610071). Here we present more evidence for it.
rate research
Read More
This paper reports the results of Suzaku observation of the spectral variation of the black hole binary LMCX-1 in the soft state. The observationwas carried out in 2009 from July 21 to 24. the obtained net count rate was $sim$30 counts s$^{-1}$ in the 0.5--50 keV band with $sim$10% peak-to-peak flux variation. The time-averaged X-ray spectrum cannot be described by a multi-color disk and single Compton component with its reflection, but requires additional Comptonized emissions. This double Compton component model allows a slightly larger inner radius of the multi-color disk, implying a lower spin parameter. Significant spectral evolution was observed above 8 keV along with a flux decrease on a timescale of $sim$10$^4$--10$^5$ s. By spectral fitting, we show that this behavior is well explained by changes in the hard Comptonized emission component in contrast to the maintained disk and soft Comptonized emission.
(Shortened) Ultraviolet observations of the black hole X-ray binary Cygnus X-1 were obtained using the STIS on HSTubble. We detect P Cygni line features show strong, broad absorption components when the X-ray source is behind the companion star and noticeably weaker absorption when the X-ray source is between us and the companion star. We fit the P Cygni profiles using the SEI method applied to a spherically symmetric stellar wind subject to X-ray photoionization from the black hole. The Si IV doublet provides the most reliable estimates of the parameters of the wind and X-ray illumination. The velocity $v$ increases with radius $r$ according to $v=v_infty(1-r_star/r)^beta$, with$betaapprox0.75$ and $v_inftyapprox1420$ km s$^{-1}$.The microturbulent velocity was $approx160$ km s$^{-1}$. Our fit implies a ratio of X-ray luminosity to wind mass-loss rate of L$_{X,38}/dot M_{-6} approx 0.33$, measured at $dot M_{-6}$ = 4.8. Our models determine parameters that may be used to estimate the accretion rate onto the black hole and independently predict the X-ray luminosity. Our predicted L$_x$ matches that determined by contemporaneous RXTE ASM remarkably well, but is a factor of 3 lower than the rate according to Bondi-Hoyle-Littleton spherical wind accretion. We suggest that some of the energy of accretion may go into powering a jet.
Orbital variability has been found in the X-ray hardness of the black hole candidate Cygnus X-1 during the soft/high X-ray state using light curves provided by the Rossi X-ray Timing Explorers All Sky Monitor. We are able to set broad limits on how the mass-loss rate and X-ray luminosity vary between the hard and soft states. The folded light curve shows diminished flux in the soft X-ray band at phase 0 (defined as the time of of the superior conjunction of the X-ray source). Models of the orbital variability provide slightly superior fits when the absorbing gas is concentrated in neutral clumps and better explain the strong variability in hardness. In combination with the previously established hard/low state dips, our observations give a lower limit to the mass loss rate in the soft state (Mdot<2x10^{-6} Msun/yr) than the limit in the hard state (Mdot<4x10^{-6} Msun/yr). Without a change in the wind structure between X-ray states, the greater mass-loss rate during the low/hard state would be inconsistent with the increased flaring seen during the high-soft state.
We present the results from the RXTE observations of Cygnus X-1 in its high state. In the energy range of 2-200 keV, the observed X-ray spectrum can be described by a model consisting of a soft blackbody component and a broken power-law with a high energy cutoff. The low energy spectrum (below about 11 keV) varies significantly from observation to observation while the high energy portion changes little. The X-ray flux varies on all timescales down to milliseconds. The power density spectrum (PDS) can be characterized by excess red noise (``1/f) at low frequencies and a white noise component that extends to 1-3 Hz before being cut off. At higher frequencies, the PDS becomes power-law again, with a slope of roughly -2 (i.e., ``1/f^2). Broad peaks in the range of 3-9 Hz are present, and might be due to quasi-periodic oscillations. The PDS shows interesting spectral dependence: the 1/f component becomes more prominent when the low-energy spectrum becomes softer. The difference in the observed spectral and timing properties between the low and high states is qualitatively consistent with a simple ``fluctuating corona model.
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 the 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.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
