Measurements using Optic and RF Waves

Chapter 11High Precision Pulsar Timing in CentimetricRadioastronomy¹

 

 

 

11.1. Introduction

Pulsars are very compact astrophysical objects detected via periodic signal and characterized by an exceptional stability — competing with the best man-made clocks. Those quasi-perfect clocks, spread throughout the Galaxy and sometimes embedded in excessively strong gravitational fields are used for many different studies. Two Nobel Prizes in Physics were already awarded for pulsar related works. In 1974, the first prize celebrated the discovery of pulsars. The second prize celebrated the discovery of binary pulsars and confirmation of general relativity in 1993. Continuing instrumental developments, always at the state of the art of the technology, are ever stimulated by the extraordinary capabilities provided by those astronomical objects. After a short description of the numerous scientific applications, we will describe the different methods used to time as precisely as possible, the regular radio pulses received from those objects. We will point out the coherent dedispersion method and we will demonstrate the astonishing possibilities of this method with several results obtained at the Nançay radiotelescope in France.

11.2. Ultra-stable clocks to the limits of the Galaxy

During studies of the interplanetary radio scintillation in 1967, highly magnetized neutron stars were discovered by serendipity (Hewish et al., 1968). Received as periodic pulses from unknown radio sources, they ...