The Crab pulsar seen with Aqueye at Asiago Cima Ekar Observatory

TL;DR

This paper presents the development and deployment of the Aqueye photon-counter instrument at Asiago Observatory, enabling high-precision optical timing of the Crab pulsar and revealing long-term stability in its pulse shape and inclination angle.

Contribution

Introduction of the Aqueye photon-counter with unprecedented timing accuracy for studying rapid variability in astrophysical sources.

Findings

High-quality optical timing data of the Crab pulsar obtained.

Evidence for decadal stability of the pulsar's inclination angle.

Potential for future improvements using GNSS time signals.

Abstract

We are developing fast photon-counter instruments to study the rapid variability of astrophysical sources by time tagging photon arrival times with unprecedented accuracy, making use of a Rubidium clock and GPS receiver. The first realization of such optical photon-counters, dubbed Aqueye (the Asiago Quantum Eye), was mounted in 2008 at the 182cm Copernicus Observatory in Asiago. Aqueye observed the Crab pulsar several times and collected data of extraordinary quality that allowed us to perform accurate optical timing of the Crab pulsar and to study the pulse shape stability on a timescale from days to years with an excellent definition. Our results reinforce the evidence for decadal stability of the inclination angle between the spin and magnetic axis of the Crab pulsar. Future realizations of our instrument will make use of the Galileo Global Navigation Satellite System (GNSS) time signal.