Counterpart candidates to the unidentified Fermi source 0FGL J1848.6-0138

Abstract

Aims. We aim to contribute to the identification of the counterpart for one of the bright sources of gamma-rays in the catalogue obtained and released by the Fermi collaboration. Methods. Our work is based on a extensive identification of sources from different wavelength catalogues and databases. Results. As a first result, we report the finding of a few counterpart candidates inside the 95% confidence error box of the Fermi LAT unidentified gamma-ray source 0FGL J1848.6−0138. The globular cluster GLIMPSE-C01 is remarkably distinctive being among the most peculiar objects consistent with both the position uncertainty in the gamma-ray source and a conceivable physical scenario for gamma-ray production. The Fermi-observed spectrum is compared with theoretical predictions in the literature and the association is found to be plausible but not yet certain because of its low X-ray to gamma-ray luminosity ratio. Other competing counterparts are also discussed. In particular, we pay special attention to a possible Pulsar Wind Nebula inside the Fermi error box, whose nature is yet to be confirmed. Conclusions. Both a globular cluster and an infrared source resembling a Pulsar Wind Nebula were found to be in positional agreement with 0FGL J1848.6−0138. In addition, other interesting objects in the field are also reported. Future gamma-ray observations will reduce the position uncertainty and we hope eventually confirm one of the counterpart candidates reported here. If GLIMPSE-C01 is confirmed together with the possible Fermi detection of the well known globular cluster 47 Tuc, then this would provide strong support to theoretical predictions that globular clusters are possible gamma-ray sources.