Young energetic PSR J1617-5055, its underluminous nebula and unidentified TeV source HESS J1616-508

Abstract

We observed the young energetic pulsar J1617-5055 with the Chandra ACIS detector for 60 ks. In addition to the pulsar, the X-ray images show a faint pulsar-wind nebula (PWN) seen up to ~1' from the pulsar. Deconvolution and reconstruction of the image reveal a brighter compact PWN component of ~1'' size, possibly with a jet-torus morphology. The PWN spectrum fits an absorbed power-law (PL) model with the photon index Gamma=1.5. The total PWN luminosity in the 0.5-8 keV band, L_{pwn}=3.2\times10^{33} ergs s^{-1} for d=6.5 kpc, is a fraction of 2\times 10^{-4} of the pulsar's spin-down power and a fraction of 0.2 of the pulsar's X-ray luminosity, which is a factor of 20 lower than one would expect from an average empirical relation found for a sample of PWNe observed with Chandra. The pulsar's spectrum can be described by an absorbed PL with n_{H}=3.5\times10^{22} cm^{-2} and Gamma=1.1, harder than any other pulsar spectrum reliably measured in the soft X-ray band. This non-thermal emission is 50% pulsed showing one peak per period. We have also investigated a possible connection between J1617 and the extended TeV source HESS J1616-508 whose center is located about 10' west of the pulsar. We find no preferential extension of the X-ray PWN toward the TeV source. Therefore, the Chandra data do not provide conclusive evidence for PSR J1617-5055 and HESS J1616-508 association. We have also analyzed archival X-ray, radio, and IR data on the HESS J1616-508 region and found traces of diffuse emission (resembling a shell in the radio) coinciding with the central part of HESS J1616-508. We speculate that the TeV source may be multiple, with most of the emission coming from an unknown SNR or a star-forming region, while some fraction of the TeV emission still may be attributed to the J1617 PWN.