The Transient Nature of GRO J1655-40 and Its Evolutionary State
Abstract
We consider the evolutionary state of the black hole X-ray source GRO J1655-40 in the context of its transient nature. Recent optical observations show that the donor in GRO J1655-40 is an intermediate-mass star (~=2.3 Msolar) crossing the Hertzsprung gap. Usually in such systems the donor's radius expansion drives a near-Eddington or super-Eddington mass transfer rate that would sustain a persistently bright accretion disk. We show that GRO J1655-40 is close to a narrow parameter range where disk instabilities can occur. This range corresponds to a short-lived evolutionary stage in which the secondary's radius expansion stalls (or reverses), with a correspondingly lower mass transfer rate. If GRO J1655-40 belongs to this class of transients, the predicted accretion rates imply large populations of luminous persistent and transient sources, which are not seen in X-rays. The transient nature of the related system GRS 1915+105 may reflect spectral variations in a bolometrically persistent source rather than a genuine luminosity increase.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- August 1997
- DOI:
- 10.1086/310810
- arXiv:
- arXiv:astro-ph/9705238
- Bibcode:
- 1997ApJ...485L..33K
- Keywords:
-
- ACCRETION;
- ACCRETION DISKS;
- STARS: BINARIES: CLOSE;
- BLACK HOLE PHYSICS;
- STARS: INDIVIDUAL ALPHANUMERIC: GRO J1655-40;
- STARS: INDIVIDUAL ALPHANUMERIC: GRS 1915+105;
- Accretion;
- Accretion Disks;
- Stars: Binaries: Close;
- Black Hole Physics;
- Stars: Individual: Alphanumeric: GRO J1655-40;
- Stars: Individual: Alphanumeric: GRS 1915+105;
- Astrophysics
- E-Print:
- Accepted for publication in ApJ Letters. LaTeX, 10 pages, including 2 figures