PSR J1907+0602: A RADIO-FAINT GAMMA-RAY PULSAR POWERING A BRIGHT TeV PULSAR WIND NEBULA

Abstract

We present multiwavelength studies of the 106.6 ms γ-ray pulsar PSR J1907+06 near the TeV source MGRO J1908+06. Timing observations with Fermi result in a precise position determination for the pulsar of R.A. = 19^h07^m547(2), decl. = +06°02'16(2)'' placing the pulsar firmly within the TeV source extent, suggesting the TeV source is the pulsar wind nebula of PSR J1907+0602. Pulsed γ-ray emission is clearly visible at energies from 100 MeV to above 10 GeV. The phase-averaged power-law index in the energy range E > 0.1 GeV is Γ = 1.76 ± 0.05 with an exponential cutoff energy E_c = 3.6 ± 0.5 GeV. We present the energy-dependent γ-ray pulsed light curve as well as limits on off-pulse emission associated with the TeV source. We also report the detection of very faint (flux density of 3.4 μJy) radio pulsations with the Arecibo telescope at 1.5 GHz having a dispersion measure DM = 82.1 ± 1.1 cm^–3 pc. This indicates a distance of 3.2 ± 0.6 kpc and a pseudo-luminosity of L ₁₄₀₀ 0.035 mJy kpc². A Chandra ACIS observation revealed an absorbed, possibly extended, compact (4'') X-ray source with significant nonthermal emission at R.A. = 19^h07^m5476, decl. = +06°02'146 with a flux of 2.3^+0.6 _–1.4 × 10^–14 erg cm^–2 s^–1. From archival ASCA observations, we place upper limits on any arcminute scale 2-10 keV X-ray emission of ~1 × 10^–13 erg cm^–2 s^–1. The implied distance to the pulsar is compatible with that of the supernova remnant G40.5 – 0.5, located on the far side of the TeV nebula from PSR J1907+0602, and the S74 molecular cloud on the nearer side which we discuss as potential birth sites.