PSR J2021+4026 in the Gamma Cygni Region The First Variable gamma-Ray Pulsar Seen by the Fermi LAT

Allafort, A.A.AllafortBaldini, L.L.BaldiniBallet, J.J.BalletVitale, V.V.VitaleCiprini, StefanoStefanoCipriniGasparrini, DarioDarioGasparriniCutini, SaraSaraCutini2020-09-172020-09-172013-11-01https://hdl.handle.net/20.500.13025/3125The Astrophysical Journal Letters, Volume 777, Issue 1, article id. L2, <NUMPAGES>8</NUMPAGES> pp. (2013).Long-term monitoring of PSR J2021+4026 in the heart of the Cygnus region with the Fermi Large Area Telescope unveiled a sudden decrease in flux above 100 MeV over a timescale shorter than a week. The "jump" was near MJD 55850 (2011 October 16), with the flux decreasing from (8.33 0.08) 10-10 erg cm-2 s-1 to (6.86 0.13) 10-10 erg cm-2 s-1. Simultaneously, the frequency spindown rate increased from (7.8 0.1) 10-13 Hz s-1 to (8.1 0.1) 10-13 Hz s-1. Significant (>5sigma) changes in the pulse profile and marginal (<3sigma) changes in the emission spectrum occurred at the same time. There is also evidence for a small, steady flux increase over the 3 yr preceding MJD 55850. This is the first observation at gamma-ray energies of mode changes and intermittent behavior, observed at radio wavelengths for other pulsars. We argue that the change in pulsed gamma-ray emission is due to a change in emission beaming and we speculate that it is precipitated by a shift in the magnetic field structure, leading to a change of either effective magnetic inclination or effective current.gamma rays starspulsars individual PSR J2021+4026stars neutronPSR J2021+4026 in the Gamma Cygni Region The First Variable gamma-Ray Pulsar Seen by the Fermi LAT10.1088/2041-8205/777/1/L2http://adsabs.harvard.edu/abs/2013ApJ...777L...2A2013ApJ...777L...2A