Searching for $\gamma$-Ray Pulsars among Fermi Unassociated Sources: 2FGL J1906.5+0720

Abstract

We report the results from our analysis of the \textit{Fermi} Large Area Telescope data of the \textit{Fermi} unassociated source 2FGL J1906.5$+$0720, which is a high-ranked candidate pulsar. In order to better study our target, we first update the ephemeris for PSR J1907$+$0602, which is used to help remove any possible contamination due to strong emission from this nearby pulsar. From our analysis, 2FGL J1906.5$+$0720 is confirmed to have a significant low energy cutoff at $\sim$ 1~GeV in its emission (14$\sigma$--18$\sigma$ significance), consistent with those seen in young pulsars. We search for pulsations but no spin frequency signals are found in a frequency range of 0.5--32 Hz. No single model can fully describe the source's overall \fermi\ $\gamma$-ray spectrum, and the reason for this is the excess emission detected at energies of $\geq$4 GeV. The high-energy component possibly indicates emission from a pulsar wind nebula, when considering 2FGL J1906.5$+$0720 as a young pulsar. We conclude that 2FGL J1906.5$+$0720 is likely a pulsar based on the emission properties we have obtained, and observations at other energies are needed in order to confirm its pulsar nature.