Fermi-LAT constraints on the Pulsar Wind Nebula nature of HESS J1857+026

Abstract

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}$andanenergyfluxof$G(0.1$--100GeV$)=(2.71 \pm 0.52_{\rm stat} \pm 1.51_{\rm syst}) \times 10^{-11}$ergscm$^{-2}$s$^{-1}$.The$γ$-rayluminosityis$L_{PWN}^γ (0.1$--100GeV$)=(2.5 \pm 0.5_{stat} \pm 1.5_{syst}) \times 10^{35} (\frac{d}{9 kpc})^2$ergss$^{-1}$,assumingadistanceof9kpc.Thisimpliesa$γ-$rayefficiencyof$\sim$5$\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.

A&A - Year: 2012 Accepted: 05/23/12

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• The soft gamma-ray pulsar population: an high-energy overview
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• A high-magnetic-field radio pulsar survey with Swift/XRT
• Radio study of HESS J1857+026. Gamma-rays from a superbubble?
• Constraints on the collimated X-ray emission of SS 433 from the reflection on molecular clouds