PSR J2021+4026 IN THE GAMMA CYGNI REGION: THE FIRST VARIABLE γ-RAY PULSAR SEEN BY THE Fermi LAT

A. Allafort , Luca Baldini , Jean Ballet (1) , Guido Barbiellini , D. Bastieri , R. Bellazzini , E. Bonamente , E. Bottacini , T. J. Brandt (2) , J. Bregeon , Pascal Bruel (3) , R. Buehler , G. A. Caliandro , R. A. Cameron , P. A. Caraveo , C. Cecchi , R.C.G. Chaves , A. Chekhtman , G. Chiaro , R. Claus , F. d'Ammando , F. de Palma , L. Di Venere , P. S. Drell , C. Favuzzi , E. C. Ferrara , A. Franckowiak , F. Gargano (4) , D. Gasparrini , N. Giglietto , M. Giroletti , T. Glanzman , G. Godfrey , S. Guiriec , D. Hadasch (5) , A. K. Harding , M. Hayashida , K. Hayashi , E. Hays , J. Hewitt , D. Horan (3) , T. Jogler , M. Kerr , Jürgen Knödlseder , J. Lande , S. Larsson , L. Latronico , M. Lemoine-Goumard , F. Longo , F. Loparco (4) , P. Lubrano , D. Malyshev , M. Marelli , M. Mayer , M. N. Mazziotta , J. Mehault (6) , T. Mizuno , M. E. Monzani , A. Morselli , S. Murgia , N. Omodei , M. Orienti , E. Orlando , D. Paneque , M. Pesce-Rollins , M. Pierbattista (1) , F. Piron (6) , G. Pivato , T.A. Porter , R. Rando , M. Razzano , T. Reposeur (7) , A. Sartori , P. M. Saz Parkinson , C. Sgro , P. Spinelli , A. W. Strong , H. Takahashi , J. B. Thayer , D. J. Thompson , L. Tibaldo , M. Tinivella , D. F. Torres , G. Tosti , Y. Uchiyama , T. L. Usher , J. Vandenbroucke , V. Vasileiou (6) , C. Venter , G. Vianello , V. Vitale , B. L. Winer , K. S. Wood

1 AIM (UMR7158 / UMR_E_9005 / UM_112) - Astrophysique Interprétation Modélisation
2 IRAP - Institut de recherche en astrophysique et planétologie
3 LLR - Laboratoire Leprince-Ringuet
4 INFN, sezione di Bari - Istituto Nazionale di Fisica Nucleare, sezione di Bari
5 IEEC-CSIC
6 LUPM - Laboratoire Univers et Particules de Montpellier
7 FERMI

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.

Mots clés: gamma rays: stars; pulsars: individual (PSR J2021+4026); stars: neutron

Domaines: Phénomènes cosmiques de haute energie [astro-ph.HE]; Phénomènes cosmiques de haute energie [astro-ph.HE]

A. Allafort, Luca Baldini, Jean Ballet, Guido Barbiellini, D. Bastieri, et al.. PSR J2021+4026 IN THE GAMMA CYGNI REGION: THE FIRST VARIABLE γ-RAY PULSAR SEEN BY THE Fermi LAT. The Astrophysical journal letters, 2013, 777, pp.L2. ⟨10.1088/2041-8205/777/1/L2⟩. ⟨in2p3-00915598⟩