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X-ray variability in Galactic high-mass black hole binaries
Stockholm University, Faculty of Science, Department of Astronomy.
Responsible organisation
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.
Keyword [en]
Accretion, high-energy astrophysics, temporal variability, X-ray binaries
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Astronomy
Identifiers
URN: urn:nbn:se:su:diva-8245ISBN: 978-91-633-3548-8 (print)OAI: oai:DiVA.org:su-8245DiVA: diva2:199890
Public defence
2008-10-30, Observatoriesalen, Observatoriemuseet, Drottninggatan 120, Stockholm, 14:00
Opponent
Supervisors
Available from: 2008-10-09 Created: 2008-10-03Bibliographically approved
List of papers
1. Evolution of the 0.01–25 Hz power spectral components in Cygnus X-1
Open this publication in new window or tab >>Evolution of the 0.01–25 Hz power spectral components in Cygnus X-1
2005 In: Astronomy & Astrophysics, ISSN 0004-6361, Vol. 438, no 3, 999-1012 p.Article in journal (Refereed) Published
Identifiers
urn:nbn:se:su:diva-25516 (URN)
Note
Part of urn:nbn:se:su:diva-8245Available from: 2008-10-09 Created: 2008-10-03Bibliographically approved
2. Probing the temporal variability of Cygnus X-1 into the soft state
Open this publication in new window or tab >>Probing the temporal variability of Cygnus X-1 into the soft state
2006 In: Astronomy & Astrophysics, ISSN 0004-6361, Vol. 452, no 3, 975-984 p.Article in journal (Refereed) Published
Identifiers
urn:nbn:se:su:diva-25517 (URN)
Note
Part of urn:nbn:se:su:diva-8245Available from: 2008-10-09 Created: 2008-10-03Bibliographically approved
3. Vanishing hardness-flux correlation in Cygnus X-1: signs of the disc moving out
Open this publication in new window or tab >>Vanishing hardness-flux correlation in Cygnus X-1: signs of the disc moving out
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.

Keyword
accretion, accretion disks -- X-rays: binaries -- X-rays: individuals: Cyg X-1
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:su:diva-25518 (URN)10.1051/0004-6361:200810172 (DOI)
Available from: 2008-10-09 Created: 2008-10-03 Last updated: 2017-12-13Bibliographically approved
4. Cygnus X-1 evolution and the origin of long duration gamma-ray bursts without supernovae
Open this publication in new window or tab >>Cygnus X-1 evolution and the origin of long duration gamma-ray bursts without supernovae
Show others...
Manuscript (Other academic)
Identifiers
urn:nbn:se:su:diva-25519 (URN)
Note
Part of urn:nbn:se:su:diva-8245Available from: 2008-10-09 Created: 2008-10-03 Last updated: 2010-01-13Bibliographically approved
5. The aperiodic broad-band X-ray variability of Cygnus X-3
Open this publication in new window or tab >>The aperiodic broad-band X-ray variability of Cygnus X-3
2009 (English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 394, no 3, 1544-1550 p.Article in journal (Refereed) Published
Abstract [en]

We study the soft X-ray variability of Cygnus X-3. By combining data from the All-Sky Monitor and Proportional Counter Array instruments on the RXTE satellite with EXOSAT/Medium Energy (ME) detector observations, we are able to analyse the power density spectrum (PDS) of the source from 10−9 to 0.1 Hz, thus covering time-scales from seconds to years. As the data on the longer time-scales are unevenly sampled, we combine traditional power spectral techniques with simulations to analyse the variability in this range. The PDS at higher frequencies (≳10−3 Hz) are for the first time compared for all states of this source. We find that it is for all states well described by a power law, with index ∼−2 in the soft states and a tendency for a less steep power law in the hard state. At longer time-scales, we study the effect of the state transitions on the PDS, and find that the variability below ∼10−7 Hz is dominated by the transitions. Furthermore, we find no correlation between the length of a high/soft-state episode and the time since the previous high/soft state. On intermediate time-scales, we find evidence for a break in the PDS at time-scales of the order of the orbital period. This may be interpreted as evidence for the existence of a tidal resonance in the accretion disc around the compact object, and constraining the mass ratio to M2/M1≲ 0.3.

Keyword
accretion, accretion discs;stars: individual: Cyg X-3;X-rays: binaries
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:su:diva-25520 (URN)10.1111/j.1365-2966.2009.14434.x (DOI)000264820500030 ()
Available from: 2008-10-09 Created: 2008-10-03 Last updated: 2017-12-13Bibliographically approved

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