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Titolo: S-curves of X-ray heated accretion discs and the black hole soft X-ray transients
Autore: El-Khoury, W; Wickramasinghe, D;
- Indirizzi:
- Australian Natl Univ, Astrophys Theory Ctr, Canberra, ACT 0200, Australia Australian Natl Univ Canberra ACT Australia 0200 rra, ACT 0200, Australia Australian Natl Univ, Dept Math, Canberra, ACT 0200, Australia Australian Natl Univ Canberra ACT Australia 0200 rra, ACT 0200, Australia
- Titolo Testata:
- MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
fascicolo: 2,
volume: 303,
anno: 1999,
pagine: 380 - 392
- SICI:
- 0035-8711(19990221)303:2<380:SOXHAD>2.0.ZU;2-S
- Fonte:
- ISI
- Lingua:
- ENG
- Soggetto:
- EVOLUTION; BINARIES; SYSTEMS; DISKS;
- Keywords:
- accretion, accretion discs; instabilities; binaries : general; X-rays : bursts; X-rays : general;
- Tipo documento:
- Article
- Natura:
- Periodico
- Settore Disciplinare:
- Physical, Chemical & Earth Sciences
- Citazioni:
- 13
- Recensione:
- Indirizzi per estratti:
- Indirizzo: El-Khoury, W Australian Natl Univ, Astrophys Theory Ctr, Canberra, ACT 0200, Australia Australian Natl Univ Canberra ACT Australia 0200 , Australia
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- Citazione:
- W. El-Khoury e D. Wickramasinghe, "S-curves of X-ray heated accretion discs and the black hole soft X-ray transients", M NOT R AST, 303(2), 1999, pp. 380-392
Abstract
It has recently been suggested that the thermal stability of accretion discs in the high (M) over dot regime may be influenced by X-rays that irradiate the disc. We investigate this problem by calculating the vertical structure of externally X-ray irradiated accretion discs using a two-stream bi-grey approximation for radiative transfer. The effects of X-ray heating depend on the hardness of the incident X-ray spectrum, and on the magnitude of the X-ray flux relative to the viscously generated flux. For heating by softX-rays, a temperature inversion occurs in the upper atmosphere of the discwhen X-ray heating dominates. For heating by hard X-rays, no significant X-ray inversion occurs. In general, the S-curves become increasingly distorted as the irradiation flux increases. The location of the upper critical point of the S-curve, and the corresponding critical mass transfer rate (M) over dot(crit) above which the disc is thermally stable, is significantly reduced if the heating is predominantly by soft X-rays. Our results are used to discuss the stability of accretion discs in black hole (BH) soft X-ray transients (SXTs). In particular, we show that the BH-SXTs lie below the X-ray irradiated instability lines, and that the BH-SXT GRO1655-40 is in the regime where the disc instability is first triggered close to the outer edgeof the disc.
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Documento generato il 25/05/13 alle ore 16:32:46