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RX J1856.5$-$3754 is the brightest and nearest ($sim 120$ pc) source among thermally emitting isolated neutron stars. Its spectra observed with {sl XMM-Newton} and {sl Chandra} satellites are well-fitted with the two-temperature ($kT^infty sim$ 32 and 63 eV) blackbody model. Fitting ten sets of the data from {sl Suzaku} XIS0, XIS1, XIS3 and {sl XMM-Newton} EPIC-pn with the two-temperature blackbody model, we discover an excess emission, 16--26% in 0.8--1.2,keV. We examine possible causes of this keV-X-ray excess; uncertainty in the background, pile up of the low energy photons and confusion of other sources. None of them succeeds in explaining the keV-X-ray excess observed with different instruments. We thus consider this keV-X-ray excess is most likely originated in RX J1856.5$-$3754. However, it is difficult to constrain the spectral shape of the keV-X-ray excess. The third blackbody component with $kT^infty = 137^{+18}_{-14}$ eV, additional power-law component with a photon index $Gamma = 3.4^{+0.5}_{-0.6}$, or Comptonization of blackbody seed photons into power-law with a photon index $Gamma_c = 4.3^{+0.8}_{-0.8}$ can reproduce the keV-X-ray excess. We also search for the periodicity of 0.8--1.2,keV data, since 7.055 s pulsation is discovered from 0.15--1.2,keV band in the XMM Newton EPIC-pn data ($sim$1.5%). We only obtain the upper limit of pulsed fraction $<$ 3% in the keV-X-ray excess. We shortly discuss the possible origin of the keV-X-ray excess, such as synchrotron radiation and Comptonization of blackbody photons.
We report on submillimetre bolometer observations of the isolated neutron star RX J1856.5--3754 using the LABOCA bolometer array on the Atacama Pathfinder Experiment (APEX) Telescope. No cold dust continuum emission peak at the position of RX J1856.5
The enigma source, RX J1856.5-3754, is one of the so-called dim thermal neutron stars. Two puzzles of RXJ1856.5-3754 exist: (1) the observational X-ray spectrum is completely featureless; (2) the UV-optical intensity is about seven times larger than
The evolution of magnetic field in isolated neutron stars is one of the most important ingredients in the attempt to build a unified description of these objects. A prediction of field evolution models is the existence of an equilibrium configuration
X-ray observations unveiled various types of radio-silent Isolated Neutron Stars (INSs), phenomenologically very diverse, e.g. the Myr old X-ray Dim INS (XDINSs) and the kyr old magnetars. Although their phenomenology is much diverse, the similar per
We report on a detailed spectral analysis of all the available XMM-Newton data of RX J1856.5-3754, the brightest and most extensively observed nearby, thermally emitting neutron star. Very small variations (~1-2%) in the single-blackbody temperature