Change search
ReferencesLink to record
Permanent link

Direct link
Vanishing hardness-flux correlation in Cygnus X-1: signs of the disc moving out
Stockholm University, Faculty of Science, Department of Astronomy.
Stockholm University, Faculty of Science, Department of Astronomy.
Responsible organisation
2008 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 490, no 1, 253-258 p.Article in journal (Refereed) Published
Abstract [en]

We investigate observations of the X-ray binary Cygnus X-1 with unusually high hardness and low flux. In particular, we study the characteristic frequencies seen in the PDS and the hardness-flux correlation within and between these observations.Methods. We analyse observations of Cyg X-1 during periods when the source reaches its highest hardness levels (1 for the 9–20 keV over 2–4 keV RXTE/PCA count ratios, corresponding to

). Using the relativistic precession model to interpret the PDS, we estimate a value for the inner radius of the accretion disc. We also study the hardness-flux correlation.Results. In the selected observations, the characteristic frequencies seen in the power spectrum are shifted to the lowest end of their frequency range. Within a single observation, the hardness-flux correlation is very weak, contrary to the negative correlation normally observed in the hard state. We suggest that this could be interpreted as the inner disc boundary being at large radii (50 ), thereby requiring more time to adjust to a changing accretion rate than allowed by a single RXTE observation, and compare our findings to estimates of the viscous time scale responsible for small scale variability in the system.

Place, publisher, year, edition, pages
2008. Vol. 490, no 1, 253-258 p.
Keyword [en]
accretion, accretion disks -- X-rays: binaries -- X-rays: individuals: Cyg X-1
National Category
Astronomy, Astrophysics and Cosmology
URN: urn:nbn:se:su:diva-25518DOI: 10.1051/0004-6361:200810172OAI: diva2:199887
Available from: 2008-10-09 Created: 2008-10-03 Last updated: 2011-05-16Bibliographically approved
In thesis
1. X-ray variability in Galactic high-mass black hole binaries
Open this publication in new window or tab >>X-ray variability in Galactic high-mass black hole binaries
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The stars of the night sky can to the naked eye appear to be steady and unchanging, apart from the twinkling created by air moving in the atmosphere. However, when viewed in X-rays, the sky is far from constant, with detectable changes occurring on very short timescales.

Black hole X-ray binaries are strong sources of X-rays. These systems contain a star and a black hole in orbit around each other. As matter from the companion star is accreted by the black hole, large amounts of gravitational energy are released, giving rise to strong X-ray emission. The accretion flow close to a black hole is characterized by strong gravity, high-energy radiation and variability on timescales down to milliseconds. These systems allow us to probe physics under conditions we cannot recreate in a laboratory, and provide some of the strongest observational indications of the existence of black holes. Temporal analysis is a powerful diagnostic of the geometry and physical processes of this environment.

The bulk of this thesis concerns studies of the rapid variability of perhaps the most well-known of all black hole binaries: Cygnus X-1. By tapping into the large amount of archival data available, a systematic study of the variability, in the form of the power spectrum, is conducted. The results show that timing studies can indeed give valuable information on the emission mechanisms and accretion geometry. Tying characteristic frequencies to effects predicted by general relativity directly gives information about the parameters of the compact object. Using these results, the past evolution of the binary system is studied.

In addition, results from temporal analysis of the possible black hole binary Cygnus X-3 are presented. The study of X-ray variability covers timescales from years to seconds, and shows that while temporal analysis provides clues to this complex system, it does not provide immediate insight into the accretion geometry, or the nature of the compact object

Place, publisher, year, edition, pages
Lidingö: Xvanen, 2008. 47 p.
Accretion, high-energy astrophysics, temporal variability, X-ray binaries
National Category
Astronomy, Astrophysics and Cosmology
Research subject
urn:nbn:se:su:diva-8245 (URN)978-91-633-3548-8 (ISBN)
Public defence
2008-10-30, Observatoriesalen, Observatoriemuseet, Drottninggatan 120, Stockholm, 14:00
Available from: 2008-10-09 Created: 2008-10-03Bibliographically approved

Open Access in DiVA

No full text

Other links

Publisher's full text

Search in DiVA

By author/editor
Axelsson, MagnusLarsson, Stefan
By organisation
Department of Astronomy
In the same journal
Astronomy and Astrophysics
Astronomy, Astrophysics and Cosmology

Search outside of DiVA

GoogleGoogle Scholar
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

Altmetric score

Total: 38 hits
ReferencesLink to record
Permanent link

Direct link