Phase resolved deadtime of the Crab pulsar using IXPE data

TL;DR

This paper develops and validates a formula to correct for detector deadtime effects on the Crab pulsar's folded light curve in X-ray data, enabling more accurate studies of its emission mechanisms.

Contribution

It introduces a simple correction formula for deadtime distortion in pulsar light curves and applies it to IXPE data, improving analysis accuracy.

Findings

Derived a deadtime distortion formula validated with NICER and NUSTAR data.

Developed a correction method for IXPE data with intermediate deadtime.

Confirmed the importance of undistorted FLC for understanding pulsar emission features.

Abstract

After receiving an X-ray photon, an X-ray detector is not operational for a duration known as deadtime. It is detector specific and its effect on the data depends upon the luminosity of the source. It reduces the observed photon count rate in comparison to the expected one. In periodic sources such as the Crab pulsar, it can distort the folded light curve (FLC). An undistorted FLC of the Crab pulsar is required in combination with its polarization properties for studying its X-ray emission mechanism. This work derives a simple formula for the distortion of the FLC of a pulsar caused by the detector deadtime, and validates it using Crab pulsar data from the X-ray observatories {{\it NICER}} and {{\it NUSTAR}}, which have very small and relatively large detector deadtimes respectively. Then it derives a method for correcting the distorted FLC of the Crab pulsar in {{\it IXPE}} data, which has intermediate detector deadtime. The formula is verified after addressing several technical issues. This work ends with a discussion of why an undistorted FLC is important for studying the formation of cusps in the FLC of the Crab pulsar.