An eclipsing millisecond pulsar with a possible main-sequence companion in NGC 6397

We present the results of one year of pulse timing observations of PSR J1740-5340, an eclipsing millisecond pulsar located in the globular cluster NGC 6397. We have obtained detailed orbital parameters and a precise position for the pulsar. The radio pulsar signal shows frequent interactions with the atmosphere of the companion, and suffers significant and strongly variable delays and intensity variations over a wide range of orbital phases. These characteristics and the binary parameters indicate that the companion may be a bloated main-sequence star or the remnant (still filling its Roche lobe) of the star that spun up the pulsar. In both cases, this would be the first binary millisecond pulsar system with such a companion.