Radio observations of the low-mass X-ray binary 2S 0921-630

The low-mass X-ray binary 2S 0921-630 has an orbital period of 9 d and therefore might be a Z source. To test this, we have performed 6 cm continuum observations of the low-mass X-ray binary 2S 0921-630 using the Australia Telescope Compact Array. The source was not detected and we determined an upper limit of 0.5 mJy (4σ) at 4.8 GHz. Comparing with earlier observations, we estimate that the probability that 2S 0921-630 has similar radio properties as prototype Z source Cyg X-2 is ∼4%