The isolated neutron star candidate 2XMM J104608.7-594306

TL;DR

This paper investigates the properties of the candidate isolated neutron star 2XMM J104608.7-594306, analyzing its X-ray and optical data to determine if it is a cooling neutron star or an accreting one, contributing to understanding INS diversity.

Contribution

It presents detailed observational analysis of a new INS candidate, supporting the cooling neutron star scenario consistent with population models, and discusses the accretion possibility.

Findings

The source is consistent with a distant cooling INS in the Carina Nebula.

It is fainter, hotter, and more absorbed than previous ROSAT INSs.

Accretion scenario requires very slow neutron star velocity (~10 km/s).

Abstract

Over the last decade, X-ray observations unveiled the existence of several classes of isolated neutron stars (INSs) which are radio-quiet or exhibit radio emission with properties much at variance with those of ordinary radio pulsars. The identification of new sources is crucial in order to understand the relations among the different classes and to compare observational constraints with theoretical expectations. A recent analysis of the 2XMMp catalogue provided less than 30 new thermally emitting INS candidates. Among these, the source 2XMM J104608.7-594306 appears particularly interesting because of the softness of its X-ray spectrum and of the present upper limits in the optical, which imply a logarithmic X-ray-to-optical flux ratio greater than 3.1, corrected for absorption. We present the X-ray and optical properties of 2XMM J104608.7-594306 and discuss its nature in the light of two possible scenarios invoked to explain the X-ray thermal emission from INSs: the release of residual heat in a cooling neutron star, as in the seven radio-quiet ROSAT-discovered INSs, and accretion from the interstellar medium. We find that the present observational picture of 2XMM J104608.7-594306 is consistent with a distant cooling INS with properties in agreement with the most up-to-date expectations of population synthesis models: it is fainter, hotter and more absorbed than the seven ROSAT sources and possibly located in the Carina Nebula, a region likely to harbour unidentified cooling neutron stars. The accretion scenario, although not entirely ruled out by observations, would require a very slow (~10 km/s) INS accreting at the Bondi-Hoyle rate.