The $\gamma$-ray pulsar J0633+0632 in X-rays

TL;DR

This study analyzes Chandra X-ray data of the gamma-ray pulsar J0633+0632, revealing an absorption feature, characterizing its thermal and non-thermal emission, constraining its distance, and suggesting its origin in the Rosette nebula.

Contribution

First detailed X-ray spectral analysis of pulsar J0633+0632, identifying an absorption feature and constraining its temperature, distance, and origin.

Findings

Detected an absorption feature at 804 eV.

Constrained the pulsar's distance to 1-4 kpc.

Identified the pulsar's temperature as one of the coldest for its class.

Abstract

We analysed Chandra observations of the bright Fermi pulsar J0633+0632 and found evidence of an absorption feature in its spectrum at $804^{+42}_{-26}$ eV (the errors here and below are at 90% confidence) with equivalent width of $63^{+47}_{-36}$ eV. In addition, we analysed in detail the X-ray spectral continuum taking into account correlations between the interstellar absorption and the distance to the source. We confirm early findings by Ray et al. (2011) that the spectrum contains non-thermal and thermal components. The latter is equally well described by the blackbody and magnetised atmosphere models and can be attributed to the emission from the bulk of the stellar surface in both cases. The distance to the pulsar is constrained in a range of 1--4 kpc from the spectral fits. We infer the blackbody surface temperature of $108^{+22}_{-14}$ eV, while for the atmosphere model, the temperature, as seen by a distant observer, is $53^{+12}_{-7}$ eV. In the latter case J0633+0632 is one of the coldest middle-aged isolated neutron stars with measured temperatures. Finally, it powers an extended pulsar wind nebula whose shape suggests a high pulsar proper motion. Looking backwards the direction of the presumed proper motion we found a likely birthplace of the pulsar -- the Rosette nebula, a 50-Myr-old active star-forming region located at about 1$.\!\!^\circ$5 from the pulsar. If true, this constrains the distance to the pulsar in the range of 1.2--1.8 kpc.