PSR J2021+4026 in the Gamma Cygni Region: The First Variable γ-Ray Pulsar Seen by the Fermi LAT
Abstract
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 (>5σ) changes in the pulse profile and marginal (<3σ) 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 γ-ray energies of mode changes and intermittent behavior, observed at radio wavelengths for other pulsars. We argue that the change in pulsed γ-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.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- November 2013
- DOI:
- 10.1088/2041-8205/777/1/L2
- arXiv:
- arXiv:1308.0358
- Bibcode:
- 2013ApJ...777L...2A
- Keywords:
-
- gamma rays: stars;
- pulsars: individual: PSR J2021+4026;
- stars: neutron;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- 12 pages, 4 figures, 1 table. Accepted for publication by ApJ Letters. Contact authors: M. Razzano (massimiliano.razzano@pi.infn.it), L. Tibaldo (ltibaldo@slac.stanford.edu)