Astrophysical Journal Letters 652,2 (2006) L109-L112;
We present high-resolution X-ray images taken with the Chandra X-Ray Observatory of the field that contains the unidentified TeV gamma-ray source HESS J1804-216. A total of 11 discrete sources were detected with a posteriori significance of > 5 sigma over the entire field of view. Among them, only one, designated as CXOU J180351.4-213707, is significantly extended. The source is about 40" away from the radio pulsar PSR J1803-2137, which was the target of the Chandra observation but was not detected in X-rays. A natural question is whether the two sources are physically related. While it is conceivable that CXOU J180351.4-213707 could be associated with a previously unknown supernova remnant (SNR), in which the pulsar was born, it seems equally plausible that it might be a pulsar wind nebula (PWN) that is powered by a different pulsar whose emission is beamed away from us. In either case, we argue that CXOU J180351.4-213707 is likely the X-ray counterpart of HESS J1804-216, based on the fact that the Galactic TeV gamma-ray sources are predominantly SNRs or PWNe. The X-ray spectrum of the source can be well fitted with a power law, although the model is not well constrained due to large statistical uncertainties. The spectrum seems to be very hard, with a best-fit photon index of about 1.2. Under the assumption that CXOU J180351.4-213707 is the X-ray counterpart of HESS J1804-216, we attempted to model the X-ray and TeV emission as synchrotron and inverse Compton scattered radiation from relativistic electrons. We briefly discuss the results.
acceleration of particles;; gamma rays : theory;; pulsars : individual (psr j1803-2137);; radiation mechanisms : nonthermal;; supernova remnants;; x-rays : general;; supernova-remnants;; synchrotron nebula;; vela pulsar;; association;; discovery
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