In-flight measurement of the absolute energy scale of the Fermi Large Area Telescope

Markus Ackermann , Marco Ajello , A. Allafort , W.B. Atwood , Magnus Axelsson , Luca Baldini , Guido Barbiellini , D. Bastieri , K. Bechtol , R. Bellazzini , B. Berenji , E.D. Bloom , E. Bonamente , A.W. Borgland , A. Bouvier , J. Bregeon , A. Brez , M. Brigidam , Pascal Bruel (1) , R. Buehler , S. Buson , G.A. Caliandro , R.A. Cameron , P. A. Caraveo , J.M. Casandjian , C. Cecchi , E. Charles , A. Chekhtman , J. Chiang , S. Ciprini , R. Claus , J. Cohen-Tanugi , S. Cutini , F. de Palmam , C.D. Dermer , S.W. Digel , E. Silva , P.S. Drell , A. Drlica-Wagner , R. Dubois , T. Enoto , L. Falletti , C. Favuzzim , S.J. Fegan (1) , W.B. Focke , P. Fortin (1) , Y. Fukazawa , S. Funk , P. Fuscom , F. Gargano , N. Gehrels , S. Germani , N. Giglietto , F. Giordano , M. Giroletti , T. Glanzman , G. Godfrey , I.A. Grenier , J.E. Grove , S. Guiriec , D. Hadasch , M. Hayashida , E. Hays , R.E. Hughes , G. Jóhannesson , A.S. Johnson , T.J. Johnson , T. Kamae , H. Katagiri , J. Kataoka , Jürgen Knödlseder (2) , M. Kuss , J. Lande , L. Latronico , S.-H. Lee , F. Longo , F. Loparco , M.N. Lovellette , P. Lubrano , G.M. Madejski , M.N. Mazziotta , J.E. Mcenery , P.F. Michelson , T. Mizuno , A.A. Moiseev , C. Monte , M.E. Monzani , A. Morselli , I.V. Moskalenko , S. Murgia , T. Nakamori , M. Naumann-Godo (3) , P.L. Nolan , J.P. Norris , E. Nuss (4) , T. Ohsugi , A. Okumura , N. Omodei , E. Orlando , J.F. Ormes , M. Ozaki , D. Paneque , J.H. Panetta , D. Parent , M. Pesce-Rollins , M. Pierbattista (3) , F. Piron (4) , S. Rainò , R. Rando , M. Razzano , A. Reimer , O. Reimer , T. Reposeur (5) , S. Ritz , L.S. Rochester , C. Sgrò , E.J. Siskind , P.D. Smith , G. Spandre , P. Spinelli , D.J. Suson , H. Takahashi , T. Tanaka , J.G. Thayer , J.B. Thayer , D.J. Thompson , L. Tibaldo , G. Tosti , E. Troja , T.L. Usher , J. Vandenbroucke , V. Vasileiou (4) , G. Vianello , N. Vilchez (2) , V. Vitale , A.P. Waite , P. Wang , B.L. Winer , K.S. Wood , Z. Yang , S. Zimmer

1 LLR - Laboratoire Leprince-Ringuet
2 IRAP - Institut de recherche en astrophysique et planétologie
3 AIM (UMR7158 / UMR_E_9005 / UM_112) - Astrophysique Interprétation Modélisation
4 LUPM - Laboratoire Univers et Particules de Montpellier
5 GLAST

The LargeAreaTelescope (LAT) on-board the Fermi Gamma-ray Space Telescope is a pair-conversion telescope designed to survey the gamma-ray sky from 20 MeV to several hundreds of GeV. In this energy band there are no astronomical sources with sufficiently well known and sharp spectral features to allow an absolute calibration of the LAT energyscale. However, the geomagnetic cutoff in the cosmic ray electron-plus-positron (CRE) spectrum in low Earth orbit does provide such a spectral feature. The energy and spectral shape of this cutoff can be calculated with the aid of a numerical code tracing charged particles in the Earth's magnetic field. By comparing the cutoff value with that measured by the LAT in different geomagnetic positions, we have obtained several calibration points between ∼6 and ∼13 GeV with an estimated uncertainty of ∼2%. An energy calibration with such high accuracy reduces the systematic uncertainty in LAT measurements of, for example, the spectral cutoff in the emission from gamma ray pulsars.

Mots clés: Cosmic-rays Geomagnetic cutoff Absolute energy scale Fermi Large Area Telescope

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

Markus Ackermann, Marco Ajello, A. Allafort, W.B. Atwood, Magnus Axelsson, et al.. In-flight measurement of the absolute energy scale of the Fermi Large Area Telescope. Astroparticle Physics, 2012, 5, pp.346-353. ⟨10.1016/j.astropartphys.2011.10.007⟩. ⟨in2p3-00684886⟩