The isolated neutron star candidate RX J1605.3+3249

TL;DR

This paper presents multi-year X-ray and optical observations of RX J1605.3+3249, identifying it as a likely nearby isolated neutron star emitting thermal radiation, with no observed variability over 6.5 years.

Contribution

It provides detailed spectral analysis and long-term observational data supporting the identification of RX J1605.3+3249 as a probable isolated neutron star.

Findings

X-ray spectrum fits a blackbody with kT = 92 +/- 6 eV

No flux or spectral variability over 6.5 years

Optical counterpart unlikely to be associated with the X-ray source

Abstract

We report on X-ray and optical observations of a ROSAT X-ray source, RX J1605.3+3249, selected from the all-sky survey on the basis of its spectral softness and lack of bright optical counterpart. The ROSAT PSPC energy distribution is well fitted by a blackbody with kT = 92 +/- 6 eV and Nh =1.1 +/- 0.4 x 10^20 cm^-2. X-ray observations spanning 6.5 years fail to reveal any flux or spectral variability on any time scales. The ROSAT HRI error circle only contains a R = 23.25 M star which is unlikely to be associated with the X-ray source. We conclude that RX J1605.3+3249 is a probable nearby isolated neutron star detected from its thermal emission. The present data do not allow to unambiguously determine the X-ray powering mechanism, cooling from a young neutron star or heating by accretion from the interstellar medium onto an old neutron star. However, the long term stability of the X-ray flux favours the young neutron star hypothesis.