Short term X-ray rms variability of Cyg X-1

A linear dependence of the amplitude of broadband noise variability on flux for GBHC and AGN has been recently shown by Uttley & McHardy (2001). We present the long term evolution of this rms-flux-relation for Cyg X-1 as monitored from 1998-2002 with RXTE. We confirm the linear relationship in the hard state and analyze the evolution of the correlation for the period of 1996-2002. In the intermediate and the soft state, we find considerable deviations from the otherwise linear relationship. A possible explanation for the rms-flux-relation is a superposition of local mass accretion rate variations.Comment: 3 pages, 3 figures, Proceedings of the 4th Microquasar Workshop, eds. Ph Durouchoux, Y. Fuchs and J. Rodriguez, published by the Center for Space Physics: Kolkat

Different kinds of long-term variability from Cygnus X-1

We present a study of the long-term variability of Cyg X-1 using data from the RXTE/ASM and the RXTE/PCA during the time between the two soft states of 1996 and 2001/2002. This period has been characterized by many short ASM flaring episodes which we have identified as "failed state transitions". The 150 d period which has been seen before and shortly after the 1996 soft state is not obviously present in the ASM rate during most of this time. Applying selection criteria from our pointed RXTE/PCA observations to exclude the flaring episodes we show that the 150 d period can indeed still be significantly detected in the hard state. Furthermore, while the ~420 d timescale associated with the flaring is reduced in the selected hard state count rate, it is still pronounced in the temporal evolution of the corresponding hardness ratios. The Ryle radio flux is also consistent with the 150 d period being present but distorted during this time.Comment: 4 pages, 6 figures, to appear in Proceedings of "X-ray Timing 2003: Rossi and Beyond", ed. P. Kaaret, F.K. Lamb, & J.H. Swan

INTEGRAL-RXTE observations of Cygnus X-1

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~50-90 keV and an optical depth of tau~1.0-1.3 plus reflection from a cold or mildly ionized slab with a covering factor of Omega/2pi~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.Comment: 6 pages, 3 figures. Figs. 2 and 3 are best viewed in color. Accepted for publication in the INTEGRAL special edition of A&A

Short-Term Radio-X-ray Correlations of Cygnus X-1

We analyze simultaneous radio-X-ray data of Cygnus X-1 from the Ryle telescope (RT) and RXTE over more than 4 a. We show that apparent correlations on short time scales in the lightcurves of Cyg X-1 are probably the coincidental outcome of white noise statistics.Comment: 1 page, 1 figure. Proceedings of the IAU Colloquium 194 "Compact Binaries in the Galaxy and Beyond", to be published in: Revista Mexicana de Astronomia y Astrofisica, Conference Serie

Rms-flux relation of Cyg X-1 with RXTE: dipping and nondipping cases

The rms (root mean square) variability is the parameter for understanding the emission temporal properties of X-ray binaries (XRBs) and active galactic nuclei (AGN). The rms-flux relation with Rossi X-ray Timing Explorer (RXTE) data for the dips and nondip of black hole Cyg X-1 has been investigated in this paper. Our results show that there exist the linear rms-flux relations in the frequency range 0.1-10 Hz for the dipping light curve. Moreover, this linear relation still remains during the nondip regime, but with the steeper slope than that of the dipping case in the low energy band. For the high energy band, the slopes of the dipping and nondipping cases are hardly constant within errors. The explanations of the results have been made by means of the ``Propagating Perturbation'' model of Lyubarskii (1997).Comment: 15 pages, 12 figures, Accepted for publication in Astrophysics & Space Scienc

The 2009 outburst of H~1743-322 as observed by RXTE

We analyze the RXTE observations of the 2009 outburst of H~1743-322, as well as the observations of the previous five outbursts for comparison. The hardness-intensity diagram (HID) shows a complete counter-clockwise q-track for the 2009 outburst and, interestingly, the track falls in} between a huge one in 2003, with a complete transition to high/soft state, and that of} the failed outburst in 2008. It leaves the low/hard state but does not reach the leftmost edge of the overall HID. While the lowest hardness (6--19 keV/3--6 keV) values} in the HID is about 0.3--0.4 for the 2009 outburst, similar to the ``failed state transition" seen in the persistent black hole XRB Cyg X-1, the timing analysis shows that a transition to the high soft state occurred. During the low/hard state of the 2009 outburst, the inner radius of the accretion disk is found to be closer to the central black hole and have an anti-correlation with the disk temperature. These results may be understood as the reprocessing} of the hot corona on the disk's} soft X-rays, which can lead to an underestimation of the inner radius of the accretion disk. In the luminosity diagram of the corona versus the disk, the tracks of the outbursts} in 2003 and 2009 cross the line which represents a roughly equal contribution to the entire emission from the thermal and the non-thermal components;} the track of the 2008 outburst has the turn-over falling} on this line. This may be indicative of an emission balance between the corona and the disk, which prevents the state transition from going further than the low/hard state.Comment: accepted by A&

The black hole candidate MAXI J1659-152: spectral and timing analysis during its 2010 outburst

We present a comprehensive spectral-timing study of the black hole candidate MAXI J1659-152 during its 2010 outburst. We analysed 65 RXTE observations taken along this period and computed the fundamental diagrams commonly used to study black hole transients. We fitted power density and energy spectra and studied the evolution of the spectral and timing parameters along the outburst. We discuss the evolution of the variability observed at different energy bands on the basis of the relative contribution of the disc and hard components to the energy spectrum of the source. We conclude that hard emission accounts for the observed fast variability, it being strongly quenched when type-B oscillations are observed. We find that both disc and hard emission are responsible for local count-rate peaks until the system reaches the soft state. From that point, the peaks are only observed in the hard component, whereas the thermal component drops monotonically probably following the accretion rate decrease. We have also computed time-lags between soft and hard X-ray variability confirming that lags are larger during the hard-to-soft transition than during the hard state.Comment: Accepted for publication in MNRAS. 12 pages, 8 figures, 2 table

The rms-flux relations in different branches in Cyg X-2

In this paper, the rms-flux (root mean square-flux) relation along the Z-track of the bright Z-Source Cyg X-2 is analyzed using the observational data of Rossi X-ray Timing Explorer (RXTE). Three types of rms-flux relations, i.e. positive, negative, and 'arch'-like correlations are found in different branches. The rms is positively correlated with flux in normal branch (NB), but anti-correlated in the vertical horizontal branch (VHB). The rms-flux relation shows an 'arch'-like shape in the horizontal branch (HB). We also try to explain this phenomenon using existing models.Comment: Accepted for publication in Astrophysics & Space Scienc