Nustar Discovery of a Young, Energetic Pulsar Associated with the Luminous Gamma-ray Source Hess J1640−465

We report the discovery of a 206 ms pulsar associated with the TeV γ-ray source HESS J1640−465 using the Nuclear Spectroscopic Telescope Array (NuSTAR) X-ray observatory. PSR J1640−4631 lies within the shell-type supernova remnant (SNR) G338.3−0.0, and coincides with an X-ray point source and putative pulsar wind nebula (PWN) previously identified in XMM-Newton and Chandra images. It is spinning down rapidly with period derivative Ṗ = 9.758(44)× 10, yielding a spindown luminosity Ė = 4.4× 10 erg s, characteristic age τc ≡ P/2Ṗ = 3350 yr, and surface dipole magnetic field strength Bs = 1.4 × 10 13 G. For the measured distance of 12 kpc to G338.3−0.0, the 0.2 − 10 TeV luminosity of HESS J1640−465 is 6% of the pulsar’s present Ė. The Fermi source 1FHL J1640.5−4634 is marginally coincident with PSR J1640−4631, but we find no γ-ray pulsations in a search using 5 years of Fermi Large Area Telescope (LAT) data. The pulsar energetics support an evolutionary PWN model for the broad-band spectrum of HESS J1640−465, provided that the pulsar’s braking index is n ≈ 2, and that its initial spin period was P0 ∼ 15 ms. Subject headings: ISM: individual (G338.3−0.0, HESS J1640−465, 1FHL J1640.5−4634) — pulsars: individual (PSR J1640−4631) — stars: neutron — supernova remnants