Radio observations of the 33.8 ms X-ray pulsar SAX J0635+0533

The hard X-ray source SAX J0635+0533 shows pulsations at a period of 33.8 m s and is thought to be associated with a bright Be star. We here report on radio observations towards this source with the VLA and Arecibo radiotelesc opes. With the VLA we do not detect any radio Aux at the Be-star position, but one 4.7 mJy (at a radio frequency of 1.4 GHz) source lies just on the b order of the 30 " X-ray error circle. Periodicity searches at 430 MHz perfo rmed with the Arecibo telescope failed to detect any pulsation. We argue th at the 4.7 mJy source is not the radio counterpart of SAX J0635+0533. Most likely SAX J0635+0533 is a rather "non-standard" Be-star/neutron-star X-ray binary pulsar, probably with a relatively short orbital period. It could s till be a radio emitting pulsar but with an emission beam not pointing towa rd the Earth.