1997A&A...323..158M

The accurate radio position of the hard X-ray transient GRS 1739-278 has been observed with different ESO telescopes in a search for optical and near infrared counterpart. A candidate counterpart has been detected in all filters observed within less than 1" of the radio position. No significant optical nor near infrared photometric variability is observed within ∼0.2mag in a time scale of several weeks. Our spectral type and reddening analysis appears to be consistent with either a normal massive X-ray binary or a low mass X-ray binary with a giant companion, both at roughly the galactic center distance. The a priori probability of a chance superposition in a field as crowded as that of GRS 1739-278 is estimated to be 14%. However, this decreases to less than 1% if the source belongs to any of the spectral types and luminosity classes proposed.