Fermi LAT observations of the Geminga pulsar

A. A. Abdo , Markus Ackermann , Marco Ajello , Luca Baldini , Jean Ballet (1) , Guido Barbiellini , D. Bastieri , B. M. Baughman , K. Bechtol , R. Bellazzini , B. Berenji , G. F. Bignami , R. D. Blandford , E. D. Bloom , E. Bonamente , A. W. Borgland , J. Bregeon (2) , A. Brez , M. Brigida , Pascal Bruel (3) , T. H. Burnett , G. A. Caliandro , R. A. Cameron , P. A. Caraveo , J. M. Casandjian (1) , C. Cecchi , O. Celik , E. Charles (1) , A. Chekhtman , C. C. Cheung , J. Chiang , S. Ciprini , R. Claus , J. Cohen-Tanugi (4) , J. Conrad , C. D. Dermer , F. de Palma , M. Dormody , E. Do Couto E Silva , P. S. Drell , R. Dubois , D. Dumora (2) , Y. Edmonds , C. Farnier (4) , C. Favuzzi , S. J. Fegan (3) , W. B. Focke , P. Fortin (3) , M. Frailis , Y. Fukazawa , S. Funk , P. Fusco , F. Gargano , D. Gasparrini , N. Gehrels , S. Germani , G. Giavitto , N. Giglietto , F. Giordano , T. Glanzman , G. Godfrey , I. A. Grenier (1) , M.-H. Grondin (2) , J. E. Grove , L. Guillemot (2) , S. Guiriec , D. Hadasch , A. K. Harding , E. Hays , R. E. Hughes , G. Johannesson , A. S. Johnson , T. J. Johnson , W. N. Johnson , T. Kamae , H. Katagiri , J. Kataoka , N. Kawai , M. Kerr , Jürgen Knödlseder (5) , M. Kuss , J. Lande , L. Latronico , M. Lemoine-Goumard (2) , F. Longo , F. Loparco , B. Lott (2) , M. N. Lovellette , P. Lubrano , A. Makeev , M. Marelli , M. N. Mazziotta , J. E. Mcenery , C. Meurer , P. F. Michelson , W. Mitthumsiri , T. Mizuno , A. A. Moiseev , C. Monte , M. E. Monzani , A. Morselli , I. V. Moskalenko , S. Murgia , P. L. Nolan , J. P. Norris , E. Nuss (4) , T. Ohsugi , N. Omodei , E. Orlando , J. F. Ormes , M. Ozaki , D. Paneque , J. H. Panetta , D. Parent (2) , V. Pelassa (4) , M. Pepe , M. Pesce-Rollins , F. Piron (4) , T.A. Porter , S. Raino , R. Rando , P. S. Ray , M. Razzano , A. Reimer , O. Reimer , T. Reposeur (2) , L. S. Rochester , A. Y. Rodriguez , R. W. Romani , M. Roth , F. Ryde , H. F.-W. Sadrozinski , A. Sander , P. M. Saz Parkinson , J. D. Scargle , C. Sgro , E. J. Siskind , David Stanley Smith (2) , P. D. Smith , G. Spandre , P. Spinelli , M. S. Strickman , D. J. Suson , H. Takahashi , T. Takahashi , T. Tanaka , J. B. Thayer , J. G. Thayer , D. J. Thompson , L. Tibaldo (1) , D. F. Torres , G. Tosti , A. Tramacere , T. L. Usher , A. van Etten , V. Vasileiou , C. Venter , N. Vilchez (5) , V. Vitale , A. P. Waite , P. Wang , K. Watters , B. L. Winer , K. S. Wood , T. Ylinen , M. Ziegler

1 AIM (UMR7158 / UMR_E_9005 / UM_112) - Astrophysique Interprétation Modélisation
2 CENBG - Centre d'Etudes Nucléaires de Bordeaux Gradignan
3 LLR - Laboratoire Leprince-Ringuet
4 LPTA - Laboratoire de Physique Théorique et Astroparticules
5 CESR - Centre d'étude spatiale des rayonnements

We report on the \textit{Fermi}-LAT observations of the Geminga pulsar, the second brightest non-variable GeV source in the $\gamma$-ray sky and the first example of a radio-quiet $\gamma$-ray pulsar. The observations cover one year, from the launch of the $Fermi$ satellite through 2009 June 15. A data sample of over 60,000 photons enabled us to build a timing solution based solely on $\gamma$ rays. Timing analysis shows two prominent peaks, separated by $\Delta \phi$ = 0.497 $\pm$ 0.004 in phase, which narrow with increasing energy. Pulsed $\gamma$ rays are observed beyond 18 GeV, precluding emission below 2.7 stellar radii because of magnetic absorption. The phase-averaged spectrum was fitted with a power law with exponential cut-off of spectral index $\Gamma$ = (1.30 $\pm$ 0.01 $\pm$ 0.04), cut-off energy $E_{0}$ = (2.46 $\pm$ 0.04 $\pm$ 0.17) GeV and an integral photon flux above 0.1 GeV of (4.14 $\pm$ 0.02 $\pm$ 0.32) $\times$ 10$^{-6}$ cm$^{-2}$ s$^{-1}$. The first uncertainties are statistical and the second are systematic. The phase-resolved spectroscopy shows a clear evolution of the spectral parameters, with the spectral index reaching a minimum value just before the leading peak and the cut-off energy having maxima around the peaks. Phase-resolved spectroscopy reveals that pulsar emission is present at all rotational phases. The spectral shape, broad pulse profile, and maximum photon energy favor the outer magnetospheric emission scenarios.

Mots clés: gamma rays: stars; pulsars: general; pulsars: individual (PSR J0633+1746; Geminga)

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

A. A. Abdo, Markus Ackermann, Marco Ajello, Luca Baldini, Jean Ballet, et al.. Fermi LAT observations of the Geminga pulsar. The Astrophysical Journal, 2010, 720, pp.272-283. ⟨10.1088/0004-637X/720/1/272⟩. ⟨in2p3-00530035⟩