Detection of very high energy radiation from HESS J1908+063 confirms the Milagro unidentified source MGRO J1908+06

Abstract

Aims. Detection of a $\gamma$-ray source above 300 GeV is reported, confirming the unidentified source MGRO J1908+06, discovered by the Milagro collaboration at a median energy of 20 TeV. Methods. The source was observed during 27 h as part of the extension of the HESS Galactic plane survey to longitudes >30 ${\hbox {$^\circ $ }}$. Results. HESS J1908+063 is detected at a significance level of 10.9$\sigma $ with an integral flux above 1 TeV of (3.76 $\pm$ 0.29 $_{\rm ~stat}\pm$ 0.75 $_{\rm sys})\times10^{-12}$ ph cm-2 s-1, and a spectral photon index $\Gamma = 2.10\pm 0.07_{\rm ~stat}\pm 0.2_{\rm sys}$. The positions and fluxes of HESS J1908+063 and MGRO J1908+06 are in good agreement. Possible counterparts at other wavelengths and the origin of the $\gamma$-ray emission are discussed. The nearby unidentified GeV source, GRO J1908+0556 (GeV) which also remains unidentified and the new Fermi pulsar 0FGL J1907.5+0617, may be connected to the TeV sourceAims. Detection of a γ-ray source above 300 GeV is reported, confirming the unidentified source MGRO J1908+06, discovered by the Milagro collaboration at a median energy of 20 TeV. Methods. The source was observed during 27 h as part of the extension of the HESS Galactic plane survey to longitudes >30°. Results. HESS J1908+063 is detected at a significance level of 10.9σ with an integral flux above 1 TeV of (3.76 ± ± )10-12 ph cm-2 s-1, and a spectral photon index Γ = 2.10±± 0.2. The positions and fluxes of HESS J1908+063 and MGRO J1908+06 are in good agreement. Possible counterparts at other wavelengths and the origin of the γ-ray emission are discussed. The nearby unidentified GeV source, GRO J1908+0556 (GeV) which also remains unidentified and the new Fermi pulsar 0FGL J1907.5+0617, may be connected to the TeV source.