<i>INTEGRAL</i>-<i>RXTE</i>observations of Cygnus X-1

Pottschmidt, K.; Wilms, J.; Chernyakova, M.; Nowak, Michael A.; Rodríguez, J.; Zdziarski, A. A.; Beckmann, V.; Kretschmar, P.; Gleissner, T.; Pooley, G. G.; Martínez-Núñez, S.; Courvoisier, T. J. L.; Schönfelder, V.; Staubert, R.

doi:10.1051/0004-6361:20031258

Cited by 30 publications

(39 citation statements)

References 28 publications

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“…The spectral parameters are in qualitative agreement with those found for Comptonization models of earlier observations (e.g., Pottschmidt et al 2003a;Di Salvo et al 2001;Frontera et al 2001;Gilfanov et al 1999;Gierliński et al 1999;Dove et al 1998). The availability of the large number of observations allows us to study the variation of the spectral parameters in this black hole candidate in unprecedented detail.…”

Section: Discussionsupporting

confidence: 88%

“…We first use the Comptonization model compTT (Titarchuk 1994;Titarchuk & Lyubarskij 1995;Titarchuk & Hua 1995), as historically it has met with good success in describing black hole spectra. Model parameters discussed here, therefore, can be used in comparisons with earlier results and other sources (see, e.g., Pottschmidt et al 2003a). Furthermore, as we shall see below, the behavior of compTT parameters is very similar to that of the more sophisticated Comptonization models, while being substantially faster to fit.…”

Section: Simple Comptonization Models: Compttmentioning

confidence: 76%

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Long term variability of Cygnus X-1

Wilms¹,

Nowak

Pottschmidt

et al. 2006

A&A

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268

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Continuing the observational campaign initiated by our group, we present the long term spectral evolution of the Galactic black hole candidate Cygnus X-1 in the X-rays and at 15 GHz. We present ∼200 pointed observations taken between early 1999 and late 2004 with the Rossi X-ray Timing Explorer and the Ryle radio telescope. The X-ray spectra are remarkably well described by a simple broken power law spectrum with an exponential cutoff. Physically motivated Comptonization models, e.g., by Titarchuk (1994, ApJ, 434, 570, compTT) and by Coppi (1999, in High Energy Processes in Accreting Black Holes, ed. J. Poutanen, & R. Svensson (San Francisco: ASP), ASP Conf. Ser., 161, 375, eqpair), can reproduce this simplicity; however, the success of the phenomenological broken power law models cautions against "overparameterizing" the more physical models. Broken power law models reveal a significant linear correlation between the photon index of the lower energy power law and the hardening of the power law at ∼10 keV. This phenomenological soft/hard power law correlation is partly attributable to correlations of broad band continuum components, rather than being dominated by the weak hardness/reflection fraction correlation present in the Comptonization model. Specifically, the Comptonization models show that the bolometric flux of a soft excess (e.g., disk component) is strongly correlated with the compactness ratio of the Comptonizing medium, with L disk ∝ ( h / s ) −0.19 . Over the course of our campaign, Cyg X-1 transited several times into the soft state, and exhibited a large number of "failed state transitions". The fraction of the time spent in such low radio emission/soft X-ray spectral states has increased from ∼10% in 1996-2000 to ∼34% since early 2000. We find that radio flares typically occur during state transitions and failed state transitions (at h / s ∼ 3), and that there is a strong correlation between the 10-50 keV X-ray flux and the radio luminosity of the source. We demonstrate that rather than there being distinctly separated states, in contrast to the timing properties the spectrum of Cyg X-1 shows variations between extremes of properties, with clear cut examples of spectra at every intermediate point in the observed spectral correlations.

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Section: Discussionsupporting

confidence: 88%

Section: Simple Comptonization Models: Compttmentioning

confidence: 76%

Long term variability of Cygnus X-1

Wilms¹,

Nowak

Pottschmidt

et al. 2006

A&A

Self Cite

146

268

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“…Also, the results are in accordance with what was obtained by SPI, and RXTE with simultaneous observations, which validates the ISGRI matrix in this energy range (Pottschmidt et al 2003).…”

Section: Tests Of the Matrices During Pv Phasesupporting

confidence: 91%

Status of the Integral/IBIS telescope modeling and of the response matrices generation

Laurent

Limousin

Cadolle-Bel

et al. 2003

A&A

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Abstract. The main objective of the IBIS modeling activities is the generation of the IBIS spectral response matrices. This generation has been done step by step by firstly constructing a "calibrated model" of each IBIS sub-system. A "calibrated model" is defined as a GEANT Monte-Carlo model, further checked by intensive corresponding calibration. These calibrated models have been in a second step integrated in the whole IBIS Mass Model. This Mass Model has been checked then using the data obtained during the IBIS telescope calibration, the Payload Ground Calibration at ESA/ESTEC, and will be refined using In-flight calibration data acquired during the whole INTEGRAL mission. The different IBIS response matrices have been generated using the IBIS Mass Model. Here we will present a status of the Mass Model and of the response matrices generation, and show with the Crab pulsar calibration data that, with the new release of the spectral extraction software by ISDC, we will have a good IBIS/ISGRI response from 20 to 600 keV.

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“…Cygnus X-1 was extensively observed (1 Ms) during the calibration phase of the mission (Bouchet et al 2003;Pottschmidt et al 2003;Bazzano et al 2003). At that time, the source presented all the characteristics of the LHS.…”

Section: Introductionmentioning

confidence: 99%

Bimodal spectral variability of Cygnus X-1 in an intermediate state

Malzac¹,

Petrucci

Jourdain³

et al. 2006

A&A

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We report the results of an observation of Cygnus X-1 performed on June 7-11, 2003 with INTEGRAL that we combine with simultaneous radio observations with the Ryle telescope. Both spectral and variability properties of the source indicate that Cygnus X-1 was in an Intermediate State. The INTEGRAL spectrum shows a high-energy cut-off or break around 100 keV. The shape of this cut-off differs from pure thermal Comptonisation, suggesting the presence of a non-thermal component at higher energies. The average broad band spectrum is well represented by hybrid thermal/non-thermal Comptonisation models. However, models with mono-energetic injection, or models with an additional soft component are favoured over standard power-law acceleration models. During the 4 day long observation the broad band (3-200 keV) luminosity varied by up to a factor of 2.6 and the source showed an important spectral variability. A principal component analysis demonstrates that most of this variability occurs through 2 independent modes. The first mode consists in changes in the overall luminosity on time scale of hours with almost constant spectra (responsible for 68% of the variance) that are strikingly uncorrelated with the variable radio flux. We interpret this variability mode as variations of the dissipation rate in the corona, possibly associated with magnetic flares. The second variability mode consists in a pivoting of the spectrum around ∼10 keV (27% of the variance). It acts on a longer time-scale: initially soft, the spectrum hardens in the first part of the observation and then softens again. This pivoting pattern is strongly correlated with the radio (15 GHz) emission: radio fluxes are stronger when the INTEGRAL spectrum is harder We propose that the pivoting mode represents a "mini" state transition from a nearly High Soft State to a nearly Low Hard State, and back. This mini-transition would be caused by changes in the soft cooling photons flux in the hot Comptonising plasma associated with an increase of the temperature of the accretion disc. The jet power then appears to be anti-correlated with the disc luminosity and unrelated to the coronal power. This is in sharp contrast with previous results obtained for the Low Hard State, suggesting a different mode of coupling between the jet, the cold disc, and the corona in Intermediate States. From this interpretation we also infer that the bolometric luminosity jumps by a factor of about 2 during the transition hard to soft, suggesting a radiatively inefficient accretion flow in the Low Hard State.

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INTEGRAL-RXTEobservations of Cygnus X-1

Cited by 30 publications

References 28 publications

Long term variability of Cygnus X-1

Long term variability of Cygnus X-1

Status of the Integral/IBIS telescope modeling and of the response matrices generation

Bimodal spectral variability of Cygnus X-1 in an intermediate state

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