OBSERVATION OF TeV GAMMA RAYS FROM THE UNIDENTIFIED SOURCE HESS J1841-055 WITH THE ARGO-YBJ EXPERIMENT

We report the observation of a very high energy gamma-ray source whose position is coincident with HESS J1841-055. This source has been observed for 4.5 years by the ARGO-YBJ experiment from 2007 November to 2012 July. Its emission is detected with a statistical significance of 5.3 standard deviations. Parameterizing the source shape with a two-dimensional Gaussian function, we estimate an extension sigma = (0.40(-0.22)(+0.32))degrees, which is consistent with the HESS measurement. The observed energy spectrum is dN/dE = (9.0 +/- 1.6) x 10(-13)(E/5 TeV)(-2.32 +/- 0.23) photons cm(-2) s(-1) TeV-1, in the energy range 0.9-50 TeV. The integral gamma-ray flux above 1 TeV is 1.3 +/- 0.4 Crab, which is 3.2 +/- 1.0 times the flux derived by HESS. The differences in the flux determination between HESS and ARGO-YBJ and possible counterparts at other wavelengths are discussed.