Wideband Pulsar Timing System

Introduction

NRAO is building a wide-band (approximately 0.5 – 3 GHz) prime-focus receiver system and matching backend with Tsys (on cold sky) of 25-30K across most of the band, to be used primarily for high-precision pulsar timing projects such as NANOGrav. This system will simultaneously capture the entire portion of the radio spectrum best suited for pulsar timing - below about 500 MHz, interstellar scattering and galactic background radiation affect the pulsar signal, while above about 3 GHz pulsars typically become too faint for high-precision measurements. Currently this frequency range can only be observed with a set of smaller-bandwidth receivers that cannot be used simultaneously. In addition to increasing total signal-to-noise ratio, the very wide band of the new receiver will improve pulsar timing by providing much more precise measurements of interstellar dispersion. It will also enable new cutting-edge research into removal of higher order frequency-dependent interstellar medium effects that can systematically limit some pulsar timing observations.

Coherently dedispersed observations (using GUPPI) of the millisecond pulsar B1821-24 over a portion of the band that would be covered by the new system. These data include the PF1 820MHz system(200 MHz of BW), L-band (800 MHz of BW centered at 1500MHz) and an additional 500 MHz of BW from the S-band system (up until the WiFi band). The proposed system would extend the lower part of the band by several hundred MHz (where pulsars are brighter) and increase the high end by over 500 MHz. Changes in the intrinsic pulse shape (ignored until only the most recent generation of wide-band pulsar systems) are blatantly obvious in the data.