An Investigation of the state changes of PSR J2021+4026 and the Vela pulsar

TL;DR

This study analyzes the gamma-ray emission variability and state changes of pulsars PSR J2021+4026 and Vela, revealing flux recovery, glitch-related magnetospheric disturbances, and the absence of long-term emission changes or high-energy photons.

Contribution

It provides new insights into the timing and flux state changes of these pulsars and their relation to glitch events, with detailed long-term gamma-ray data analysis.

Findings

PSR J2021+4026 shows flux recovery and decrease epochs.

Vela's glitch affects radio pulses but not gamma-ray emission.

No long-term gamma-ray emission change or >100 GeV photons detected.

Abstract

We investigate the high energy emission activities of two bright gamma-ray pulsars, PSR~J2021+4026 and Vela. For PSR~J2021+4026, the state changes in the gamma-ray flux and spin-down rate have been observed. We report that the long-term evolution of the gamma-ray flux and timing behavior of PSR~J2021+4026 suggests a new gamma-ray flux recovery at around MJD~58910 and a flux decrease around MJD~59500. During this epoch, the staying time, the gamma-ray flux difference and spin-down rate are smaller than previous epochs in the same state. The waiting timescale of the quasi-periodic state changes is similar to the waiting timescale of the glitch events of the Vela pulsar. For the Vela pulsar, the quench of the radio pulse was in a timescale of $\sim0.2$~s after the 2016 glitch, and the glitch may disturb the structure of the magnetosphere. Nevertheless, we did not find any evidence for a long-term change in the gamma-ray emission properties using years of $Fermi$-LAT data, and therefore, no long-term magnetosphere structural change. We also conduct searching for photons above 100~GeV using 15-year $Fermi$-LAT data, and found none. Our results provide additional information for the relation between the state change of the gamma-ray emission and the glitch event.