Letter to the Editor

Optical identification of the transient supersoft X-ray source RX J0527.8-6954, in the LMC^*

¹ IP&D, Universidade do Vale do Paraíba, Av. Shishima Hifumi, 2911, CEP 12244-000, São José dos Campos, SP, Brasil e-mail: alexandre@univap.br
² Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo, 05508-900, São Paulo, SP, Brasil

Received: 12 April 2010
Accepted: 20 June 2010

Abstract

Context. Close binary supersoft X-ray sources (CBSS) are binary systems that contain a white dwarf with stable nuclear burning on its surface. These sources, first discovered in the Magellanic Clouds, have high accretion rates and near-Eddington luminosities (10³⁷ - 10³⁸ erg s^-1) with high temperatures (T = 2–7 × 10⁵ K).

Aims. The total number of known objects in the MC is still small and, in our galaxy, even smaller. We observed the field of the unidentified transient supersoft X-ray source RX J0527.8-6954 in order to identify its optical counterpart.

Methods. The observation was made with the IFU-GMOS on the Gemini South telescope with the purpose of identifying stars with possible or Balmer emission or else of observing nebular extended jets or ionization cones, features that may be expected in CBSS.

Results. The X-ray source is identified with a B5e V star that is associated with subarcsecond extended Hα emission, possibly bipolar.

Conclusions. If the primary star is a white dwarf, as suggested by the supersoft X-ray spectrum, the expected orbital period exceeds 21 h; therefore, we believe that the 9.4 h period found so far is not associated to this system.