DISCOVERY OF AN ENERGETIC 38.5 ms PULSAR POWERING THE GAMMA-RAY SOURCE IGR J18490-0000/HESS J1849-000

We report the discovery of a 38.5 ms X-ray pulsar in observations of the soft γ-ray source IGR J18490-0000 with the Rossi X-ray Timing Explorer (RXTE). PSR J1849-0001 is spinning down rapidly with period derivative 1.42 x 10-14 s s-1, yielding a spin-down luminosity E-dot = 9.8 x 1036 erg s-1, characteristic age τc≡P/2 P-dot = 42.9 kyr, and surface dipole magnetic field strength Bs = 7.5 x 1011 G. Within the INTEGRAL/IBIS error circle lies a point-like XMM-Newton and Chandra X-ray source that shows evidence of faint extended emission consistent with a pulsar wind nebula (PWN). The XMM-Newton spectrum of the point source is well fitted by an absorbed power-law model with photon index ΓPSR = 1.1 ± 0.2, NH = (4.3 ± 0.6) x 1022 cm-2, and FPSR(2-10 keV) = (3.8 ± 0.3) x 10-12 erg cm-2 s-1, while the spectral parameters of the extended emission are roughly ΓPWN ∼ 2.1 and FPWN(2-10 keV) ∼ 9 x 10-13 erg cm-2 s-1. IGR J18490-0000 is also coincident with the compact TeV source HESS J1849-000. For an assumed distance of 7 kpc in the Scutum arm tangent region, the 0.35-10 TeV luminosity of HESS J1849-000 is 0.13% of the pulsar's spin-down energy, while the ratio F(0.35-10 TeV)/FPWN(2-10 keV) ∼ 2. These properties are consistent with leptonic models of TeV emission from PWNe, with PSR J1849-0001 in a stage of transition from a synchrotron X-ray source to an inverse Compton γ-ray source.