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Astron. Astrophys. 322, 507-510 (1997)

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The August 1993 outburst of the black hole candidate GRO J0422+32 *

A.J. Castro-Tirado 1, J.L. Ortiz 2 and J. Gallego 3

1 Laboratorio de Astrofísica Espacial y Física Fundamental (LAEFF-INTA), P.O. Box 50727, E-28080 Madrid, Spain
2 Consejo Superior de Investigaciones Científicas, Instituto de Astrofísica de Andalucía (IAA), P.O. Box 3004, E-18080 Granada, Spain
3 Departamento de Astrofísica, Universidad Complutense, Facultad de Ciencias, E-28040 Madrid, Spain

Received 29 October 1996 / Accepted 2 December 1996


One year after the X-ray outburst, the optical counterpart of the black hole candidate GRO J0422+32 underwent an unexpected one-month outburst beginning on 10 August 1993. CCD photometry was obtained for the optical counterpart with the 1.5-m telescope at Calar Alto on 6 consecutive nigths since the onset of this event, never seen before in other transients belonging to the black-hole class. Two spectra were also taken with the 2.2-m telescope on 14 August. We suggest the Mass Transfer Instability model as possible explanation of the event on the basis of the observational facts presented here.

Key words: X-ray: bursts; stars – stars: GRO J0422+32 – instabilities – accretion disks

* Based on observations collected at the German-Spanish Astronomical Center, Calar Alto, Spain, operated jointly by the Max-Planck-Institut fur Astronomie (MPIA), Heidelberg, and the Spanish National Commission for Astronomy.

Send offprint requests to: A.J. Castro-Tirado (ajct@laeff.esa.es)

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© European Southern Observatory (ESO) 1997

Online publication: June 5, 1998