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Using a 16.2 hr radio observation by the Australia Telescope Compact Array(ATCA) and archival Chandra data, we found $>5\sigma$ radio counterparts to 4known and 3 new X-ray sources within the half-light radius ($r_\mathrm{h}$) ofthe Galactic globular cluster NGC 6397. The previously suggested millisecondpulsar (MSP) candidate, U18, is a steep-spectrum ($S_\nu \propto \nu^\alpha$;$\alpha=-2.0^{+0.4}_{-0.5}$) radio source with a 5.5 GHz flux density of$54.7\pm 4.3~\mathrm{\mu Jy}$. We argue that U18 is most likely a "hidden" MSPthat is continuously hidden by plasma shocked at the collision between thewinds from the pulsar and companion star. The nondetection of radio pulsationsso far is probably the result of enhanced scattering in this shocked wind. Onthe other hand, we observed 5.5 GHz flux of the known MSP PSR J1740-5340 (U12)to decrease by a factor of $>2.8$ during epochs of 1.4 GHz eclipse, indicatingthat the radio flux is absorbed in its shocked wind. If U18 is indeed a pulsarwhose pulsations are scattered, we note the contrast with U12's flux decreasein eclipse, which argues for two different eclipse mechanisms at the same radiofrequency. In addition to U12 and U18, we also found radio associations for 5other Chandra X-ray sources, four of which are likely background galaxies. Thelast, U97, which shows strong H$\alpha$ variability, is mysterious; it may beeither a quiescent black hole low-mass X-ray binary, or something more unusual.

The MAVERIC survey: A hidden pulsar and a black hole candidate in ATCA radio imaging of the globular cluster NGC 6397