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    PSR J2021+4026 in the gamma cygni region: the first variable γ-ray pulsar seen by the Fermi LAT

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    2013PSRJ2021 2041-8205_777_1_L2.pdf (796.5Kb)
    Date
    2013
    Author
    Allafort, A.
    Venter, C.
    Baldini, L.
    Ballet, J.
    Barbiellini, G.
    Fermi LAT
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    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.
    URI
    http://hdl.handle.net/10394/10474
    https://doi.org/10.1088/2041-8205/777/1/L2
    http://iopscience.iop.org/2041-8205/777/1/L2/pdf/2041-8205_777_1_L2.pdf
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