Submillimetre observations of RX J1856.5--3754

TL;DR

This study used submillimetre observations to search for dust and gas around the neutron star RX J1856.5--3754, setting limits on dust mass and accretion, and exploring its possible interaction with a molecular cloud.

Contribution

First submillimetre observational constraints on dust and gas around RX J1856.5--3754, providing limits on dust mass and accretion rate, and suggesting a past interaction with a molecular cloud.

Findings

No cold dust emission detected, with a flux density upper limit of 5 mJy.

Cold dust mass limit of a few Earth masses established.

Accretion rate constrained to less than 10^{14} g/s.

Abstract

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--3754 was detected. The 3 sigma flux density upper limit of 5 mJy translates into a cold dust mass limit of a few earth masses. We use the new submillimetre limit, together with a previously obtained H-band limit, to constrain the presence of a gaseous, circumpulsar disc. Adopting a simple irradiated-disc model, we obtain a mass accretion limit of dM/dt less than 10^{14} g/s, and a maximum outer disc radius of around 10^{14} cm. By examining the projected proper motion of RX J1856.5--3754, we speculate about a possible encounter of the neutron star with a dense fragment of the CrA molecular cloud a few thousand years ago.