Presentation details
» Highly structured wind in Vela X-1
Presentation duration: 30 minutes
Presenter: Ingo Kreykenbohm
I present the results of an in-depth analysis of the spectral and temporal properties of a two week long uninterrupted INTEGRAL observation of Vela X-1 in Nov/Dec 2003. In addition to an already high activity level, Vela X-1 exhibited several very intense flares with a maximum intensity of more than 5 Crab in the 20--40 keV band and unexpected off states where the source became undetectable with ISGRI. I discuss a possbile scenario to explain these off states and flares in the frame work of a strongly structured wind of the donor star: The neutron star can encounter cavities with a strongly reduced density as well as dense blobs of material. When the neutron star enters such a cavity, the accretion rate will drop, thus potentially triggering the onset of the propeller effect, which then inhibits further accretion. At the same time, this structured wind can also give rise to giant flares when a large blob of dense material is accreted. Further temporal analysis revealed that a short lived QPO with a period of ~6800 sec is present in the light curve. The part of the light curve during which the QPO is present is very close to the off states and just following a high intensity state, thus showing that all these phenomena are related.
Authors:- Ingo Kreykenbohm
- Jörn Wilms
- Peter Kretschmar
- Jose Miguel Torrejon
- Katja Pottschmidt
- Manfred Hanke
- Andrea Santangelo
- Carlo Ferrigno
- Rüdiger Staubert