A study of the long term variability of RX J1856.5-3754 with XMM-Newton

TL;DR

This study analyzes XMM-Newton data of neutron star RX J1856.5-3754, finding minimal spectral variability likely due to instrumental effects, and suggests a possible slight temperature increase over several years.

Contribution

It provides the first detailed long-term spectral analysis of RX J1856.5-3754, establishing limits on variability and modeling its spectrum with two blackbody components.

Findings

Spectral variations are minimal and likely instrumental.

A potential temperature increase of about 0.15 eV/year from 2002 to 2005.

The spectrum is well modeled by two blackbody components.

Abstract

We report on a detailed spectral analysis of all the available XMM-Newton data of RX J1856.5-3754, the brightest and most extensively observed nearby, thermally emitting neutron star. Very small variations (~1-2%) in the single-blackbody temperature are detected, but are probably due to an instrumental effect, since they correlate with the position of the source on the detector. Restricting the analysis to a homogeneous subset of observations, with the source at the same detector position, we place strong limits on possible spectral or flux variations from March 2005 to present-day. A slightly higher temperature (kT~61.5 eV, compared to the average value kT~61 eV) was instead measured in April 2002. If this difference is not of instrumental origin, it implies a rate of variation of about 0.15 eV/yr between April 2002 and March 2005. The high-statistics spectrum from the selected observations is well fit by the sum of two blackbody models, which extrapolate to an optical flux level in agreement with the observed value.