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Astronomy and Astrophysics 544 (2012) A3
Fermi-LAT constraints on the Pulsar Wind Nebula nature of HESS J1857+026
R. Rousseau1, M.-H. Grondin, A. Van Etten, M. Lemoine-Goumard1, S. Bogdanov, J. W. T. Hessels, V. M. Kaspi, Z. Arzoumanian, F. Camilo, J. M. Casandjian2, C. M. Espinoza, S. Johnston, A. G. Lyne, D. A. Smith1, B. W. Stappers, G. A. Caliandro

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 gamma-ray source detected by H.E.S.S. and classified as a possible pulsar wind nebula candidate powered by PSR J1856+0245. We search for gamma-ray pulsations from PSR J1856+0245 and explore the characteristics of its associated pulsar wind nebula. Using a rotational ephemeris obtained from the Lovell telescope at Jodrell Bank Observatory at 1.5 GHz, we phase-fold 36 months of gamma-ray data acquired by the Large Area Telescope (LAT) aboard Fermi. We also perform a complete gamma-ray spectral and morphological analysis. No gamma-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 gamma-ray spectrum is well described by a simple power-law with a spectral index of 1.53 \pm 0.11_{\rm stat} \pm 0.55_{\rm syst}$ and an energy flux of $G(0.1$--100 GeV$)=(2.71 \pm 0.52_{\rm stat} \pm 1.51_{\rm syst}) \times 10^{-11}$ ergs cm$^{-2}$ s$^{-1}$. The $\gamma$-ray luminosity is $L_{PWN}^{\gamma} (0.1$--100 GeV$)=(2.5 \pm 0.5_{stat} \pm 1.5_{syst}) \times 10^{35} (\frac{d}{9 kpc})^2$ ergs s$^{-1}$, assuming a distance of 9 kpc. This implies a $\gamma-$ray efficiency of $\sim$ 5% for $\dot{E}=4.6 \times 10^{36}$ erg $s^{-1}$, in the range expected for pulsar wind nebulae. Detailed multi-wavelength modeling provides new constraints on its pulsar wind nebula nature.
1:  CENBG - Centre d'Etudes Nucléaires de Bordeaux Gradignan
2:  AIM - UMR 7158 - Astrophysique Interactions Multi-échelles
Physics/Astrophysics/High Energy Astrophysical Phenomena

Sciences of the Universe/Astrophysics/High Energy Astrophysical Phenomena