Search for gamma-ray variability around Fermi-LAT pulsar glitches

TL;DR

This study systematically examined gamma-ray emission variability around pulsar glitches using 14 years of Fermi-LAT data, finding no significant flux changes and highlighting the unique behavior of PSR J2021+4026.

Contribution

Introduced a novel systematic approach to analyze gamma-ray variability associated with pulsar glitches using likelihood-weighted spectral analysis over an extended dataset.

Findings

No significant gamma-ray flux variation detected around glitches.

The Vela pulsar's flux remains stable within 0.5% upper limit.

PSR J2021+4026 exhibits unique gamma-ray variability properties.

Abstract

Pulsars are the most numerous class of Galactic gamma-ray sources detected by the Fermi Large Area Telescope (LAT). Young pulsars occasionally experience sudden timing discontinuities called glitches, characterized by rapid changes in rotational parameters, usually followed by a return to regular rotation. PSR J2021+4026 is unique among Fermi-LAT pulsars, exhibiting quasiperiodic switches between two states with varying spin-down rates approximately every 3-4 years, correlated with sudden changes in gamma-ray emission features. This study searched for gamma-ray emission variability in pulsars correlated with glitch occurrence. We introduced a novel approach to analyzing LAT gamma-ray pulsars through systematic examination of variability associated with spin-down rate changes. We tracked rotation and gamma-ray emission changes for seven promising glitches selected based on observed spin-down rate variations. Using 14 years of Fermi-LAT data, we conducted binned likelihood spectral analysis of data windows around selected glitch epochs. We improved best-fit parameter precision by incorporating likelihood weights calculated from diffuse background models, accounting for systematic error contributions. The phase-averaged flux and spectral parameters of analyzed pulsars showed no significant variation across investigated glitches. The 95% upper limits on relative flux change indicate the Vela pulsar flux is unchanging, with a 0.5% upper limit on relative change, making it promising for further searches. The connection between glitch dynamics and gamma-ray emission remains unclear, and PSR J2021+4026 remains unique in its gamma-ray variability properties. We conclude that comprehensive investigation of glitches is warranted to further unravel their underlying mechanisms.