We report the discovery of two binary millisecond pulsars in the core-collapsed globular cluster M30 using the Green Bank Telescope ( GBT ) at 20 cm .
PSR J2140 - 2310A ( M30A ) is an eclipsing 11-ms pulsar in a 4-hr circular orbit and PSR J2140 - 23B ( M30B ) is a 13-ms pulsar in an as yet undetermined but most likely highly eccentric ( e > 0.5 ) and relativistic orbit .
Timing observations of M30A with a 20-month baseline have provided precise determinations of the pulsar ’ s position ( within 4 ^ { \prime \prime } of the optical centroid of the cluster ) , and spin and orbital parameters , which constrain the mass of the companion star to be m _ { 2 } \gtrsim 0.1 \mbox { M } _ { \odot } .
The position of M30A is coincident with a possible thermal X-ray point source found in archival Chandra data which is most likely due to emission from hot polar caps on the neutron star .
In addition , there is a faint ( V _ { 555 } \sim 23.8 ) star visible in archival HST F555W data that may be the companion to the pulsar .
Eclipses of the pulsed radio emission from M30A by the ionized wind from the compact companion star show a frequency dependent duration ( \propto \nu ^ { - \alpha } with \alpha \sim 0.4 - 0.5 ) and delay the pulse arrival times near eclipse ingress and egress by up to 2 - 3 ms. Future observations of M30 may allow both the measurement of post-Keplerian orbital parameters from M30B and the detection of new pulsars due to the effects of strong diffractive scintillation .