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Is RXJ1856.5-3754 an old neutron star?

S. Campana·S. Mereghetti·L. Sidoli
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Abstract

An unusual X-ray source, RXJ1856.5-3754, has recently been discovered with ROSAT: its spectrum resembles that of supersoft sources, but the very high X-ray to optical flux ratio excludes the presence of a companion star, pointing to an isolated compact object. It has been proposed that RXJ1856.5-3754 is an old, isolated neutron star accreting from the interstellar medium. Here we present a reanalysis of the ROSAT data. The HRI observation reveals an attitude reconstruction problem, resulting in a larger error box than previously reported. Deeper optical observations allow us to reveal a few optical counterparts inside the new error box, but the X-ray to optical flux ratio is still very high (greater than 20) and none of the candidates has peculiar colors.

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S. Campana, S. Mereghetti, L. Sidoli. 1996-10-01. Is RXJ1856.5-3754 an old neutron star?. https://arxiv.org/abs/astro-ph/9610004

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