The gravitomagnetic clock effect and pulsar timing

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Written by Eva Hackmann

In General Relativity the rotation of a gravitating object influences the spacetime in its vicinity, which is called frame dragging or gravitomagnetism. Related to this is the Lense-Thirring effect due to spin-orbit coupling, measured by the LAGEOS/LARES missions, and the Schiff effect due to spin-spin coupling, measured by the Gravity Probe B mission. Here we will discuss a frame dragging effect on clocks, the gravitomagnetic clock effect first analysed by Cohen and Mashhoon (Physics Letters A 181 (1993) 353) for the case of two clocks on counter-revolving equatorial circular orbits. We show how this effect can be defined for two clocks on arbitrary geodesic orbits in Kerr spacetime and discuss its magnitude for two pulsars orbiting Sagittarius A*.