Investigating the X-ray Emission from the Galactic TeV Gamma-ray Source MGRO J1908+06

Abstract: MGRO J1908+06 is a bright, extended TeV gamma-ray source located near the Galactic plane. The TeV emission has previously been attributed to the pulsar wind nebula of the radio-faint gamma-ray pulsar PSR J1907+0602 discovered with Fermi. However, studies of the TeV morphology with VERITAS have shown that MGRO J1908+06 is somewhat larger than other pulsar wind nebulae of similar age and that the TeV spectrum does not soften with distance from the pulsar as is observed for other pulsar wind nebulae. Although MGRO J1908+06 is very bright in gamma rays with a flux corresponding to ~80% of the Crab Nebula flux at 20 TeV, no extended emission at other energies has so far been detected. We report on our analysis of X-ray data obtained with XMM-Newton of the region near MGRO J1908+06. We searched the data for point-like sources and detected several hard-spectrum X-ray sources that could be associated with the TeV emission, including the gamma-ray pulsar PSR J1907+0602. We also performed an extended source analysis to search for diffuse emission from MGRO J1908+06 but found no evidence of diffuse X-ray emission coincident with the TeV source. We place an upper limit of $8.7\times10^{33}\rm~erg~s^{-1}$ on the X-ray luminosity of MGRO J1908+06 in the 1-10 keV energy range. The corresponding limit on the ratio of gamma-ray to X-ray luminosity is consistent with the ratios found for other pulsar wind nebulae of similar age.