Fermi LAT Observations of LS 5039

A. A. Abdo , Markus Ackermann , Marco Ajello , William B. Atwood , Magnus Axelsson , Luca Baldini , Jean Ballet (1) , Guido Barbiellini , D. Bastieri , B. M. Baughman , K. Bechtol , R. Bellazzini , B. Berenji , R. D. Blandford , E.D. Bloom , E. Bonamente , A.W. Borgland , J. Bregeon , A. Brez , M. Brigida , Pascal Bruel (2) , T.H. Burnett , S. Buson , G. A. Caliandro , R. A. Cameron , P. A. Caraveo , J.M. Casandjian (1) , E. Cavazzuti , C. Cecchi , O. Celik , S. Chaty (1) , A. Chekhtman , C.C. Cheung , J. Chiang , S. Ciprini , R. Claus , J. Cohen-Tanugi (3) , L.R. Cominski , J. Conrad , S. Corbel , R. Corbet , S. Cutini , C. D. Dermer , A. de Angelis , F. de Palma , S. W. Digel , E. Do Couto E Silva , P.S. Drell , R. Dubois , G. Dubus (4) , D. Dumora (5) , C. Farnier (3) , C. Favuzzi , S.J. Fegan (2) , W.B. Focke , P. Fortin (2) , M. Frailis , Y. Fukazawa , S. Funk , P. Fusco , F. Gargano , D. Gasparrini , N. Gehrels , S. Germani , B. Giebels (2) , N. Giglietto , F. Giordano , T. Glanzman , G. Godfrey , I.A. Grenier (1) , M.H. Grondin (5) , J.E. Grove , L. Guillemot (5) , S. Guiriec (3) , Y. Hanabata , A.K. Harding , M. Hayashida , E. Hays , A.B. Hill (4) , D. Horan (2) , R.E. Hugues , M.S. Jackson , G. Jóhannesson , T. J. Johnson , W. N. Johnson , A.S. Johnson , T. Kamae , H. Katagiri , J. Kataoka , N. Kawai , M. Kerr , Jürgen Knödlseder (6) , M. L. Kocian , F. Kuehn , M. Kuss , J. Lande , S. Larsson , L. Latronico , M. Lemoine-Goumard (5) , F. Longo , F. Loparco , B. Lott (5) , M.N. Lovellette , P. Lubrano , G. M. Madejski , 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 (3) , T. Ohsugi , N. Omodei , E. Orlando , J.F. Ormes , M. Ozaki , D. Paneque , J.H. Panetta , D. Parent (5) , V. Pelassa (3) , M. Pepe , M. Pesce-Rollins , F. Piron (3) , T.A. Porter , S. Rainò , R. Rando , P.S. Ray , M. Razzano , N. Rea , A. Reimer , O. Reimer , T. Reposeur (5) , S. Ritz , L.S. Rochester , A.Y. Rodriguez , R.W. Romani , M. Roth , F. Ryde , D. Sanchez (2) , A. Sander , P.M. Saz Parkinson , J.D. Scargle , C. Sgrò , A. Sierpowska-Bartosik , E.J. Siskind , D. A. Smith (5) , P. D. Smith , G. Spandre , P. Spinelli , M.S. Strickman , D.J. Suson , H. Tajima , H. Takahashi , T. Takahashi , T. Tanaka , Y. Tanaka , J.B. Thayer , D.J. Thompson , L. Tibaldo (1) , D.F. Torres , G. Tosti , A. Tramacere , Y. Uchiyama , T.L. Usher , V. Vasileiou , C. Venter , N. Vilchez (6) , V. Vitale , A. P. Waite , E. Wallace , P. Wang , B. L. Winer , K.S. Wood , T. Ylinen , M. Ziegler

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

The first results from observations of the high mass X-ray binary LS 5039 using the Fermi Gamma-ray Space Telescope data between 2008 August and 2009 June are presented. Our results indicate variability that is consistent with the binary period, with the emission being modulated with a period of 3.903 +/- 0.005 days; the first detection of this modulation at GeV energies. The light curve is characterized by a broad peak around superior conjunction in agreement with inverse Compton scattering models. The spectrum is represented by a power law with an exponential cutoff, yielding an overall flux (100 MeV - 300 GeV) of 4.9 +/- 0.5(stat) +/- 1.8(syst) x 10^-7 photon cm^-2 s^-1, with a cutoff at 2.1 +/- 0.3(stat) +/- 1.1(syst) GeV and photon index Gamma = 1.9 +/- 0.1(stat) +/- 0.3(syst). The spectrum is observed to vary with orbital phase, specifically between inferior and superior conjunction. We suggest that the presence of a cutoff in the spectrum may be indicative of magnetospheric emission similar to the emission seen in many pulsars by Fermi.

Mots clés: binaries: close; gamma rays: observations; stars: variables: other; X-rays: binaries; X-rays: individual (LS 5039)

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

A. A. Abdo, Markus Ackermann, Marco Ajello, William B. Atwood, Magnus Axelsson, et al.. Fermi LAT Observations of LS 5039. The Astrophysical journal letters, 2009, 706, pp.L56-L61. ⟨10.1088/0004-637X/706/1/L56⟩. ⟨in2p3-00436279⟩