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 9.758(44) × 10 −13 , yielding a spin-down luminosity 4.4 × 10 36 erg s −1 , characteristic age 3350 yr, and surface dipole magnetic field strength B s = 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 . 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 five years of Fermi Large Area Telescope (LAT) data. The pulsar energetics support an evolutionary PWN model for the broadband spectrum of HESS J1640−465, provided that the pulsar's braking index is n ≈ 2, and that its initial spin period was P 0 ∼ 15 ms.