2006A&A...447..245W


Query : 2006A&A...447..245W

2006A&A...447..245W - Astronomy and Astrophysics, volume 447, 245-261 (2006/2-3)

Long term variability of Cygnus X-1. IV. Spectral evolution 1999-2004.

WILMS J., NOWAK M.A., POTTSCHMIDT K., POOLEY G.G. and FRITZ S.

Abstract (from CDS):

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 15GHz. 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 (1994ApJ...434..570T, compTT) and by Coppi (1999, 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 ∼10keV. 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 Ldisk ∝ (lh/ls)–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 lh/ls∼3), and that there is a strong correlation between the 10-50keV 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.

Abstract Copyright:

Journal keyword(s): stars: individual: Cyg X-1 - stars: binaries: close - X-rays: binaries - black hole physics

Simbad objects: 13

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Number of rows : 13
N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2022
#notes
1 V* CM Tau Psr 05 34 31.9474694616 +22 00 52.153698024           ~ 5076 0
2 M 1 SNR 05 34 32 +22 00.8           ~ 5956 1
3 X LMC X-3 HXB 05 38 56.6323605504 -64 05 03.317937504   17 17.2     B2.5Ve 649 0
4 X LMC X-1 HXB 05 39 38.8284304464 -69 44 35.531553624   14.8 14.5     O8(f)p 604 2
5 V* IL Lup HXB 15 47 08.2768672752 -47 40 10.284587760     11.96     ~ 453 1
6 V* V381 Nor HXB 15 50 58.6637920704 -56 28 35.258385000   17.95 16.6     K3III 1103 0
7 X Nor X-1 LXB 16 34 01.610 -47 23 34.80           ~ 468 0
8 [GHJ2008] 3 HXB 16 50 00.980 -49 57 43.60     11.89     K4V 370 0
9 V* V821 Ara HXB 17 02 49.3876391280 -48 47 23.087954544 16.20 16.30 15.5     ~ 1950 0
10 NAME Slow Burster LXB 17 31 57.73 -33 50 02.5     15.50     ~ 799 1
11 [KRL2007b] 353 HXB 19 08 53.080 +09 23 04.84     15.80     ~ 101 0
12 HD 226868 HXB 19 58 21.6757355952 +35 12 05.784512688 9.38 9.72 8.91 8.42   O9.7Iabpvar 4138 0
13 V* V1408 Aql LXB 19 59 24.0074252040 +11 42 29.859773292 18.40 18.97 18.95 18.70 18.66 ~ 183 0

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2022.10.03-00:08:16

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