A deep search for the optical counterpart to the anomalous X-ray pulsar 1E 2259+58.6

TL;DR

This study used deep optical imaging to search for the counterpart of the anomalous X-ray pulsar 1E 2259+58.6, setting limits on its optical brightness and implications for its powering mechanism.

Contribution

The paper provides improved X-ray positioning and deep optical limits, constraining models of the pulsar's nature and ruling out certain accretion scenarios.

Findings

No optical counterpart detected down to R=25.7 and I=24.3 magnitudes.

Constraints suggest the pulsar is unlikely powered by accretion from a disk.

Results challenge accretion-based models for this anomalous X-ray pulsar.

Abstract

We present Keck R and I band images of the field of the anomalous X-ray pulsar 1E 2259+58.6. We derive an improved X-ray position from archival ROSAT HRI observations by correcting for systematic (boresight) errors. Within the corresponding error circle, no object is found on the Keck images, down to limiting magnitudes R = 25.7 and I = 24.3. We discuss the constraints imposed by these limits, and conclude that it is unlikely that 1E 2259+58.6 is powered by accretion from a disk, irrespective of whether it is in a binary or not, unless the binary is extremely compact.