Optical observations of the black hole candidate XTE J1550-564 during the September/October 1998 outburst

Astronomy & Astrophysics Letters 348, L9 (1999)

C. Sanchez-Fernandez [1], A. J. Castro-Tirado [1][2], H. W. Duerbeck [3], L. Mantegazza [4], V. Beckmann [5], V. Burwitz [6], L. Vanzi, [7], A. Bianchini[8], M. Della Valle [8], A. Piemonte [9], B. Dirsch [10], I. Hook [11], L. Yan [12], A. Gimenez [1][2]

  1. Laboratorio de Astrofisica Espacial y Fisica Fundamental (LAEFF-INTA), P.O. Box 50727, E-28080 Madrid, Spain
  2. Free University Brussels (VUB), Pleinlaan 2, B-1050 Brussels, Belgium
  3. Consejo Superior de Investigaciones Cientificas, Instituto de Astrofisica de Andalucia (IAA), P.O. Box 3004, E-18080 Granada, Spain
  4. Osservatorio Astronomico di Brera, Via Bianchi 46, I-23807 Merate, Italy
  5. Hamburger Sternwarte, Gojenbergsweg 112, D-21029 Hamburg, Germany
  6. Max-Planck-Institut für extraterrestische Physik, P.O. Box 1603, D-85740 Garching, Germany
  7. European Southern Observatory, Alonso de Cordova 3107, Santiago, Chile
  8. Osservatorio Astronomico di Padova, vicolo dell'Osservatorio 5, 35122 Padova, Italy
  9. Osservatorio Astrofisico di Asiago, Universita di Padova, I-36012 Asiago, Italy
  10. Sternwarte, Universität Bonn, Auf dem Hügel 71, D-53121 Bonn, Germany
  11. European Southern Observatory, Karl-Schwarzschild-Strasse 2, D-85748 Garching bei München, Germany
  12. Carnegie Observatories, 813 Santa Barbara St., Pasadena, CA 91101, USA


We report here optical observations during the September/October 1998 outburst of the black hole candidate XTE J1550-564. CCD photometry was obtained for the optical counterpart with the 0.9m Dutch telescope at La Silla since the onset of this event. We analysed 211 U, V and i frames, from Sep 10 to Oct 23. Stochastic flaring activity was observed on Sep 11-16, but no evidence for a superhump period, as seen in other soft X-ray transients, was found. An optical flare nearly simultaneous to an X-ray flare that occurred on Sep 21 was observed in the V-band. A reddened optical spectrum showed the typical emission lines corresponding to X-ray transients in outburst. From the interstellar absorption lines, we derive E(B-V) = 0.70 +/- 0.10 and suggest a distance of about 2.5 kpc. In such case, MB = +7 mag for the progenitor, which is consistent with the spectral type of a low-mass K0-K5 main-sequence companion.

Key words: Black hole physics - Stars: neutron - Stars: binaries: general - X-rays: general

Contact: Volker Beckmann.

Preprint (compressed PS-File, 70 Kb)