High variability in Vela X-1: giant flares and off states
Kreykenbohm I, Wilms J, Kretschmar P, Torrejon JM, Pottschmidt K, Hanke M, Santangelo A, Ferrigno C, Staubert R (2008)
Publication Status: Published
Publication Type: Journal article
Publication year: 2008
Journal
Publisher: EDP SCIENCES S A
Book Volume: 492
Pages Range: 511-525
Journal Issue: 2
DOI: 10.1051/0004-6361:200809956
Abstract
Aims. We investigate the spectral and temporal behavior of the high mass X-ray binary Vela X-1 during a phase of high activity, with special focus on the observed giant flares and off states.Methods. INTEGRAL observed Vela X-1 in a long almost uninterrupted observation for two weeks in 2003 Nov/Dec. The data were analyzed with OSA 7.0 and FTOOLS 6.2. We derive the pulse period, light curves, spectra, hardness ratios, and hardness intensity diagrams, and study the eclipse.Results. In addition to an already high activity level, Vela X-1 exhibited several intense flares, the brightest ones reaching a maximum intensity of more than 5 Crab in the 20-40 keV band and several off states where the source was no longer detected by INTEGRAL. We determine the pulse period to be 283.5320 +/- 0.0002 s, which is stable throughout the entire observation. Analyzing the eclipses provided an improvement in the ephemeris. Spectral analysis of the flares indicates that there appear to be two types of flares: relatively brief flares, which can be extremely intense and show spectral softening, in contrast to high intensity states, which are longer and show no softening.Conclusions. Both flares and off states are interpreted as being due to a strongly structured wind of the optical companion. When Vela X-1 encounters a cavity with strongly reduced density, the flux will drop triggering the onset of the propeller effect, which inhibits further accretion, giving rise to off states. The sudden decrease in the density of the material required to trigger the propeller effect in Vela X-1 is of the same order as predicted by theoretical papers about the densities in OB star winds. A similarly structured wind can produce giant flares when Vela X-1 encounters a dense blob in the wind.
Authors with CRIS profile
Ingo Kreykenbohm
Dr.Karl-Remeis-Sternwarte Bamberg, Astronomisches Institut
Jörn Wilms
Professur für Astronomie und Astrophysik
Manfred Hanke
Dr.Karl-Remeis-Sternwarte Bamberg, Astronomisches Institut
Involved external institutions
European Space Astronomy Centre (ESAC)
Spain (ES)
Kepler Center for Astro and Particle Physics
Germany (DE)
University of Maryland
United States (USA) (US)
University of Alicante / Universidad de Alicante / Universitat d'Alacant
Spain (ES)
Spain (ES)
Kepler Center for Astro and Particle Physics
Germany (DE)
University of Maryland
United States (USA) (US)
University of Alicante / Universidad de Alicante / Universitat d'Alacant
Spain (ES)
How to cite
APA:
Kreykenbohm, I., Wilms, J., Kretschmar, P., Torrejon, J.M., Pottschmidt, K., Hanke, M.,... Staubert, R. (2008). High variability in Vela X-1: giant flares and off states. Astronomy & Astrophysics, 492(2), 511-525. https://dx.doi.org/10.1051/0004-6361:200809956
MLA:
Kreykenbohm, Ingo, et al. "High variability in Vela X-1: giant flares and off states." Astronomy & Astrophysics 492.2 (2008): 511-525.
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