Identification of a Likely Radio Counterpart to the Rapid Burster

We have identified a likely radio counterpart to the low-mass X-ray binaryMXB 1730-335 (the Rapid Burster). The counterpart has shown 8.4 GHz radioon/off behavior correlated with the X-ray on/off behavior as observed by theRXTE/ASM during six VLA observations. The probability of an unrelated, randomlyvarying background source duplicating this behavior is 1-3% depending on thecorrelation time scale. The location of the radio source is RA 17h 33m 24.61s;Dec -33d 23' 19.8" (J2000), +/- 0.1". We do not detect 8.4 GHz radio emissioncoincident with type II (accretion-driven) X-ray bursts. The ratio of radio toX-ray emission during such bursts is constrained to be below the ratio observedduring X-ray persistent emission at the 2.9-sigma level. Synchrotron bubblemodels of the radio emission can provide a reasonable fit to the full data set,collected over several outbursts, assuming that the radio evolution is the samefrom outburst to outburst, but given the physical constraints the emission ismore likely to be due to ~hour-long radio flares such as have been observedfrom the X-ray binary GRS 1915+105.