A possible association of the new VHE gamma-ray source HESS J1825--137 with the pulsar wind nebula G18.0--0.7

F.A. Aharonian , A.G. Akhperjanian , A.R. Bazer-Bachi , M. Beilicke , W. Benbow , D. Berge , K. Bernlohr , C. Boisson , O. Bolz , V. Borrel , I. Braun , F. Breitling , A.M. Brown , P.M. Chadwick , L.-M. Chounet (1) , R. Cornils , L. Costamante , B. Degrange (1) , H.J. Dickinson , A. Djannati-Ataï (2) , L.O'C. Drury , G. Dubus (1) , D. Emmanoulopoulos , P. Espigat (2) , F. Feinstein (3) , G. Fontaine (1) , Y. Fuchs , S. Funk , Y.A. Gallant (3) , B. Giebels (1) , S. Gillessen , J.F. Glicenstein , P. Goret , C. Hadjichristidis , M. Hauser , G. Heinzelmann , G. Henri , G. Hermann , J.A. Hinton , W. Hofmann , M. Holleran , D. Horns , A. Jacholkowska (3) , O.C. de Jager , B. Khelifi , Nu. Komin , A. Konopelko , I.J. Latham , R. Le Gallou , A. Lemiere (2) , M. Lemoine-Goumard (1) , N. Leroy (1) , T. Lohse , J.M. Martin , O. Martineau-Huynh (4) , A. Marcowith , C. Masterson , T.J.L. Mccomb , M. de Naurois (4) , S.J. Nolan , A. Noutsos , K.J. Orford , J.L. Osborne , M. Ouchrif (4) , M. Panter , G. Pelletier , S. Pita (2) , G. Puhlhofer , M. Punch (2) , B.C. Raubenheimer , M. Raue , J. Raux (4) , S.M. Rayner , A. Reimer , O. Reimer , J. Ripken , L. Rob (1) , L. Rolland (4) , G. Rowell , V. Sahakian , L. Sauge , S. Schlenker , R. Schlickeiser , C. Schuster , U. Schwanke , M. Siewert , H. Sol , D. Spangler , R. Steenkamp , C. Stegmann , J.-P. Tavernet (4) , R. Terrier (2) , C.G. Theoret (2) , M. Tluczykont (1) , G. Vasileiadis (3) , C. Venter , P. Vincent (4) , H.J. Volk , S.J. Wagner

1 LLR - Laboratoire Leprince-Ringuet
2 APC (UMR_7164) - AstroParticule et Cosmologie
3 LPTA - Laboratoire de Physique Théorique et Astroparticules
4 LPNHE - Laboratoire de Physique Nucléaire et de Hautes Énergies

We report on a possible association of the recently discovered very high-energy $\gamma$-ray source HESS J1825--137 with the pulsar wind nebula (commonly referred to as G 18.0--0.7) of the $2.1\times 10^{4}$ year old Vela-like pulsar PSR B1823--13. HESS J1825--137 was detected with a significance of 8.1 $\sigma$ in the Galactic Plane survey conducted with the H.E.S.S. instrument in 2004. The centroid position of HESS J1825--137 is offset by 11\arcmin south of the pulsar position. \emph{XMM-Newton} observations have revealed X-ray synchrotron emission of an asymmetric pulsar wind nebula extending to the south of the pulsar. We argue that the observed morphology and TeV spectral index suggest that HESS J1825--137 and G 18.0--0.7 may be associated: the lifetime of TeV emitting electrons is expected to be longer compared to the {\it XMM-Newton} X-ray emitting electrons, resulting in electrons from earlier epochs (when the spin-down power was larger) contributing to the present TeV flux. These electrons are expected to be synchrotron cooled, which explains the observed photon index of $\sim 2.4$, and the longer lifetime of TeV emitting electrons naturally explains why the TeV nebula is larger than the X-ray size. Finally, supernova remnant expansion into an inhomogeneous medium is expected to create reverse shocks interacting at different times with the pulsar wind nebula, resulting in the offset X-ray and TeV $\gamma$-ray morphology.

Domaines: Cosmologie et astrophysique extra-galactique [astro-ph.CO]; Astrophysique [astro-ph]

F.A. Aharonian, A.G. Akhperjanian, A.R. Bazer-Bachi, M. Beilicke, W. Benbow, et al.. A possible association of the new VHE gamma-ray source HESS J1825--137 with the pulsar wind nebula G18.0--0.7. Astronomy and Astrophysics - A&A, 2005, 442, pp.L25-L29. ⟨10.1051/0004-6361:200500180⟩. ⟨in2p3-00025035⟩