Study of the gamma-ray state changes of PSR J2021+4026 with Fermi-LAT

Abstract

The peculiar radio-quiet PSR J2021+4026, in the Gamma Cygni supernova remnant, is one of the brightest of the over 250 pulsars detected by Fermi-LAT. It is unique in being the only known isolated gamma-ray pulsar to undergo abrupt flux changes, which are also simultaneous with spin-down variations. The first change was observed by Fermi-LAT in October 2011, and it was followed by a recovery over a timescale of 100 days around December 2014. A second change occurred in February 2018. In the last few years, PSR J2021+4026 has been widely studied at different wavelengths. We report our latest results on this source, based on a Fermi-LAT analysis of its gamma-ray variability. In particular, we have studied the changes in the spectral and timing parameters on different timescales. Our results are essential to relate the observed events to changes in the geometry of the particle acceleration regions in the pulsar magnetosphere. Therefore, this study will allow us to enhance our knowledge of this source and its behavior.

An update on Fermi-LAT transients in the Galactic plane, including strong activity of Cygnus X-3 in mid-2020

“…This pulsar experienced a decrease in flux near 2011 October 16 (Allafort et al 2013 ) that corresponds to the end of the high-γ -rayflux state reported in Table 1 . In addition to that dimming event in 2011, further γ -ray state changes of PSR J2021 + 4026 in 2014 and 2018 were reported by Fiori et al ( 2022 ). We found the flux changes in 2014 December and 2018 February with significances of 10.3 σ and 10.4 σ each confirming the result reported by Fiori et al ( 2022 ).…”

“…In addition to that dimming event in 2011, further γ -ray state changes of PSR J2021 + 4026 in 2014 and 2018 were reported by Fiori et al ( 2022 ). We found the flux changes in 2014 December and 2018 February with significances of 10.3 σ and 10.4 σ each confirming the result reported by Fiori et al ( 2022 ). They also reported that PSR J2021 + 4026 was in its low flux state from 2018 February 2 to 2020 May 26.…”

“…The search showed that in addition to the dimming event in 2011 listed in Table 1 , the pulsar, PSR J2021 + 4026, experienced two flaring events, one was between 2014 and 2018 and the other started in 2020. The former had recently been reported by Fiori et al ( 2022 ) and the latter had not been reported. The second flaring event in Cygnus X-3 lasted for two weeks corresponds to a soft X-ray state in 2018 August.…”

A new mode change in the variable gamma-ray pulsar PSR J2021+4026

“…We ran the binned likelihood analysis on each interval separately, keeping all the spectral parameters free to vary. This was not possible our previous report due to a different choice of the spectral model [9]. Therefore, it represents an improvement in our capability of characterizing spectral variations.…”

“…We report on an updated LAT monitoring activity of PSR J2021+4026 that allowed the detection of a new mode change occurred around June 2020. This work also brings improvement to the spectral analysis compared to our previous report [9]. The manuscript is outlined as follows.…”