Investigating the origins of TeV gamma-ray emission of MGRO J1908+06 with VERITAS*

MGRO J1908+06 is a bright TeV gamma-ray source. Since its discovery by the Milagro water Cherenkov telescope, it has been detected by H.E.S.S., VERITAS, ARGO-YBJ, HAWC, and Fermi-LAT. Despite the evident detections in the TeV regime, searches for a counterpart in the radio and X-ray domains have been unsuccessful, and the nature of the TeV gamma-ray production remains unknown. The accelerator candidates in the vicinity include PSR J1907+0602 (leptonic contributor) and SNR G40.5-0.5 (hadronic contributor). This analysis aims to provide new insights into the origin of the MGRO J1908+06 emission with additional VERITAS data targeted on the regions of dense molecular clouds, the application of a newly developed background estimation method for large extended gamma-ray sources, and comparisons with 12CO observation data. An energy-dependent morphology study shows that high-energy (>4 TeV) gamma rays are concentrated toward the location of PSR J1907+0602, which confirms the association with the pulsar. Meanwhile, the new VERITAS data reveals that a newly identified gamma-ray hot spot coincides with a high-density cloud, which suggests additional hadronic component in the region. Several scenarios of the gamma-ray production, which accommodate the uncertainties of distance to the accelerator candidates (including PSR J1907+0602 and SNR G40.5-0.5) mentioned in the recent literature, are also investigated.