Discovery of a keV-X-ray Excess in RX J1856.5--3754

Understand

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.