Speaker
Description
Pulsar-black hole (BH) binary systems, which have not been found yet, are unique celestial laboratories for testing relativistic theories of gravity and understanding the formation of gravitational wave sources. We study the self gravitational lensing effect in a Pulsar-BH system. Because this effect from the BH magnifies the pulsar signal once per orbital period, we find that it may generate apparently ultra-long period ($\sim$hours) radio signal when the intrinsic pulsar signal is weak or the system is at large distances. When the lensed source is a millisecond pulsar, the Shapiro delay would cause an observationally discernable shape distortion of the lensed pulses. The number of such observable systems is estimated. The result shows that there may be hundreds of such systems in our galaxy that are observable for a radio telescope with a sensitivity of $\sim 10\,mJy$. The model is applied to two recently found puzzling long-period radio sources: J162759.5-523504.3 and PSR J0901-4046. If these two sources are self-lensed pulsar-BH systems, the BH mass will be $\sim 10^4$ and $\sim 10^2$ solar masses, respectively. Their coalescence time will become so small ($\sim$ year) that they should have merged by now.
