Fermi-LAT constraints on the pulsar wind nebula nature of HESS J1857+026
R. Rousseau1⋆, M.-H. Grondin2,3, A. Van Etten4, M. Lemoine-Goumard1⋆, S. Bogdanov5, J. W. T. Hessels6,7, V. M. Kaspi8, Z. Arzoumanian9, F. Camilo5, J. M. Casandjian10, C. M. Espinoza11, S. Johnston12, A. G. Lyne11, D. A. Smith1, B. W. Stappers11 and G. A. Caliandro13
1 Centre d’Études Nucléaires de Bordeaux Gradignan, Université Bordeaux 1, CNRS/IN2p3, 33175 Gradignan, France
e-mail: email@example.com; firstname.lastname@example.org
2 Max-Planck-Institut für Kernphysik, 69029 Heidelberg, Germany
3 Landessternwarte, Universität Heidelberg, Königstuhl, 69117 Heidelberg, Germany
4 W. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USA
5 Columbia Astrophysics Laboratory, Columbia University, New York, NY 10027, USA
6 ASTRON, The Netherlands Institute for Radio Astronomy, Postbus 2, 7990 AA, Dwingeloo, The Netherlands
7 Astronomical Institute “Anton Pannekoek”, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands
8 Department of Physics, McGill University, Montreal, PQ H3A 2T8, Canada
9 X-ray Astrophysics Laboratory and CRESST, NASA Goddard Space Flight Center, Code 662, Greenbelt, MD 20771, USA
10 Laboratoire AIM, CEA-IRFU/CNRS/Université Paris Diderot, Service d’Astrophysique, CEA Saclay, 91191 Gif-sur-Yvette, France
11 Jodrell Bank Centre for Astrophysics, School of Physics and Astronomy, The University of Manchester, M13 9PL, UK
12 CSIRO Astronomy and Space Science, Australia Telescope National Facility, Epping NSW 1710, Australia
13 Institut de Ciències de l’Espai (IEEE-CSIC), Campus UAB, 08193 Barcelona, Spain
Received: 20 December 2011
Accepted: 23 May 2012
Context. Since its launch, the Fermi satellite has firmly identified 5 pulsar wind nebulae plus a large number of candidates, all powered by young and energetic pulsars. HESS J1857 + 026 is a spatially extended γ-ray source detected by H.E.S.S. and classified as a possible pulsar wind nebula candidate powered by PSR J1856 + 0245.
Aims. We search for γ-ray pulsations from PSR J1856+0245 and explore the characteristics of its associated pulsar wind nebula.
Methods. Using a rotational ephemeris obtained from the Lovell telescope at Jodrell Bank Observatory at 1.5 GHz, we phase-fold 36 months of γ-ray data acquired by the Large Area Telescope (LAT) aboard Fermi. We also perform a complete γ-ray spectral and morphological analysis.
Results. No γ-ray pulsations were detected from PSR J1856+0245. However, significant emission is detected at a position coincident with the TeV source HESS J1857 + 026. The γ-ray spectrum is well described by a simple power-law with a spectral index of Γ = 1.53 ± 0.11stat ± 0.55syst and an energy flux of G(0.1–100 GeV) = (2.71 ± 0.52stat ± 1.51syst) × 10-11 erg cm-2 s-1. The γ-ray luminosity is LPWNγ (0.1–100 GeV)=(2.5 ± 0.5stat ± 1.5syst) × 1035 (d/9 kpc)2 erg s-1, assuming a distance of 9 kpc. This implies a γ-ray efficiency of ~5% for Ė = 4.6 × 1036 erg s-1, in the range expected for pulsar wind nebulae. Detailed multi-wavelength modeling provides new constraints on its pulsar wind nebula nature.
Key words: pulsars: general / pulsars: individual: PSR J1856+0245 / ISM: individual objects: HESS J1857+026 / gamma rays: general
© ESO, 2012