Simultaneous Absolute Timing of the Crab Pulsar at Radio and Optical Wavelengths

TL;DR

This study precisely measures the time delay between radio and optical emissions from the Crab Pulsar, providing insights into emission mechanisms and site locations across wavelengths.

Contribution

It presents the most accurate optical-radio lag measurement for the Crab Pulsar using simultaneous high-resolution observations, reducing previous uncertainties.

Findings

Optical pulse arrives 255 ± 21 microseconds after the radio pulse.

Evidence suggests a spectral dependence of optical emission linked to giant radio pulses.

Enhanced timing accuracy constrains pulsar emission models.

Abstract

The Crab pulsar emits across a large part of the electromagnetic spectrum. Determining the time delay between the emission at different wavelengths will allow to better constrain the site and mechanism of the emission. We have simultaneously observed the Crab Pulsar in the optical with S-Cam, an instrument based on Superconducting Tunneling Junctions (STJs) with $\mu$s time resolution and at 2 GHz using the Nan\c{c}ay radio telescope with an instrument doing coherent dedispersion and able to record giant pulses data. We have studied the delay between the radio and optical pulse using simultaneously obtained data therefore reducing possible uncertainties present in previous observations. We determined the arrival times of the (mean) optical and radio pulse and compared them using the tempo2 software package. We present the most accurate value for the optical-radio lag of 255 $\pm$ 21 $\mu$s and suggest the likelihood of a spectral dependence to the excess optical emission asociated with giant radio pulses.