INTEGRAL and RXTE power spectra of Cygnus X-1

doi:10.1016/j.asr.2005.04.032

Advances in Space Research

Volume 38, Issue 7, 2006, Pages 1350-1353

https://doi.org/10.1016/j.asr.2005.04.032 Get rights and content

Abstract

We evaluate 0.03–20 Hz power spectra of the bright black hole binary Cyg X-1 obtained from non-deconvolved INTEGRAL-ISGRI event data. The ISGRI power spectra are compared to contemporary RXTE-PCA ones in the same hard X-ray energy band of 15–70 keV. They agree well in shape. Since the ISGRI power spectrum of Cyg X-1 is not background corrected it lies about an order of magnitude below the PCA values. In 2003 a soft outburst of Cyg X-1 occurred. From the RXTE-ASM and Ryle radio long term lightcurves and the RXTE spectra we see a canonical “hard state–intermediate state–soft state” evolution. We discuss the evolution of the power spectra in the 15–70 keV range which so far is much less well studied than that at softer energies. We interpret our results regarding the origin of certain variability components.

Section snippets

Introduction and data extraction

Timing studies of black hole binaries allow for a very precise state classification and are essential for understanding the accretion process in these objects (Kalemci et al., 2004, Pottschmidt et al., 2003). In this work, we analyze continuum power spectra derived from the Soft Gamma-Ray Imager (ISGRI; Lebrun et al., 2003) on-board ESAs International Gamma-Ray Astrophysics Laboratory (INTEGRAL; Winkler et al., 2003), i.e., of the upper layer of the coded mask imager IBIS. By comparing

Comparison of ISGRI and PCA power spectra

Comparing typical PCA (2003-03-22) and ISGRI (2003-03-24) hard state 15–70 keV power spectra, we find that they agree well in shape up to ∼5 Hz where the ISGRI power spectrum becomes noise dominated (Fig. 2). However, the variability measured with ISGRI lies about an order of magnitude too low. This can mainly be attributed to the much higher ISGRI background and can in principle be corrected. Note that the normalization of the power spectrum scales as 1/(S + B), where S is the source count rate

Evolution over the flare

The rise of the outburst in 2003 is regularly sampled by INTEGRAL and RXTE observations. We concentrate on these observations, pointing out that also the remaining ones behave as expected from Fig. 1. Black hole binary timing behavior is usually characterized in the soft X-ray band: for the 2003 flare rise we find that the <4 keV PCA power spectra display a characteristic state transition sequence which is fully consistent with the spectral evolution. A similar sequence of power spectra has

Summary and conclusions

•
Contemporary INTEGRAL-ISGRI and RXTE-PCA 15–70 keV power spectra of Cyg X-1 are consistent in shape (data up to 2003-02-09 have to be rise-time filtered and suffer from additional instrumental effects).
•
Before deriving absolute rms values from the ISGRI power spectra, a background correction is required. In the case of Cyg X-1, the uncorrected power is an order of magnitude too low. A better characterization of the background influence is work in progress.
•
This is one of only a few studies

Acknowledgements

This work has been financed by Deutsches Zentrum für Luft- und Raumfahrt Grants 50 OG 95030, 50 OG 9601, and 50 OG 302 as well as the KBN Grants PBZ-KBN-054/P03/2001, and 1P03D01827. We thank all people involved in building and calibrating INTEGRAL for their efforts, and E. Smith and J. Swank for the very smooth scheduling of the RXTE observations.

References (9)

E. Churazov et al.
Soft state of Cygnus X-1: stable disc and unstable corona
Mon. Not. Roy. Astron. Soc.
(2001)
E. Kalemci et al.
A close look at the state transitions of galactic black hole transients during outburst decay
Astrophys. J.
(2004)
D.A. Leahy et al.
On searches for pulsed emission with application to four globular cluster X-ray sources: NGC 1851, 6441, 6624, and 6712
Astrophys. J.
(1983)
F. Lebrun et al.
ISGRI: the integral soft gamma-ray imager
Astron. Astrophys.
(2003)

There are more references available in the full text version of this article.

Cited by (7)

The INTEGRAL view on black hole X-ray binaries
2021, New Astronomy Reviews
Citation Excerpt :
Pottschmidt et al. (2003) were able to obtain 15–70 keV PDS using ISGRI, focusing on a flaring episode, while Cabanac et al. (2011) used SPI up to 130 keV, concentrating on long-term averaged PDS for the LHS and the HSS. The power spectral shapes are generally consistent with those seen at lower energies with RXTE (Pottschmidt et al., 2006b; Grinberg et al., 2015 and references therein) and can be described by a sum of several Lorentzian components which show a characteristic dependency on the spectral hardness of the source (Grinberg et al., 2014). These studies showed that Cyg X-1 varies significantly up to at least 130 keV.
INTEGRAL is an ESA mission in fundamental astrophysics that was launched in October 2002. It has been in orbit for over 18 years, during which it has been observing the high-energy sky with a set of instruments specifically designed to probe the emission from hard X-ray and soft $γ$ -ray sources. This paper is devoted to the subject of black hole binaries, which are among the most important sources that populate the high-energy sky. We present a review of the scientific literature based on INTEGRAL data, which has significantly advanced our knowledge in the field of relativistic astrophysics. We briefly summarise the state-of-the-art of the study of black hole binaries, with a particular focus on the topics closer to the INTEGRAL science. We then give an overview of the results obtained by INTEGRAL and by other observatories on a number of sources of importance in the field. Finally, we review the main results obtained over the past 18 years on all the black hole binaries that INTEGRAL has observed. We conclude with a summary of the main contributions of INTEGRAL to the field, and on the future perspectives.
Astrophysics of X-Ray Binary Spectra
2023, Defect and Diffusion Forum
The integral view on black hole x-ray binaries
2021, arXiv
Long term variability of Cygnus X-1: VI. Energy-resolved X-ray variability 1999-2011
2014, Astronomy and Astrophysics
Timing analysis with INTEGRAL: Comparing different reconstruction Algorithms
2011, Acta Polytechnica
The X-ray power spectral density function of the seyfert active galactic nucleus NGC 7469
2010, Astrophysical Journal

View all citing articles on Scopus

View full text

INTEGRAL and RXTE power spectra of Cygnus X-1

Abstract

Section snippets

Introduction and data extraction

Comparison of ISGRI and PCA power spectra

Evolution over the flare

Summary and conclusions

Acknowledgements

Soft state of Cygnus X-1: stable disc and unstable corona

Mon. Not. Roy. Astron. Soc.

A close look at the state transitions of galactic black hole transients during outburst decay

Astrophys. J.

On searches for pulsed emission with application to four globular cluster X-ray sources: NGC 1851, 6441, 6624, and 6712

Astrophys. J.

ISGRI: the integral soft gamma-ray imager

Astron. Astrophys.