Chandra X-ray and Gemini near-infrared observations of the eclipsing msec pulsar SWIFT J1749.4-2807 in quiescence

TL;DR

This study combines Chandra X-ray and Gemini near-infrared observations to identify and analyze the potential counterpart of the eclipsing millisecond pulsar SWIFT J1749.4-2807 in quiescence, aiming to facilitate neutron star mass measurements.

Contribution

First near-infrared identification of the pulsar's counterpart in quiescence, providing positional data and candidate sources for future spectroscopic follow-up.

Findings

Identified a candidate near-infrared source consistent with X-ray position.

Detected potential variability in the brighter candidate source.

Provided precise localization to aid future mass measurements.

Abstract

We report on Chandra X-ray and Gemini-North near-infrared K-band observations of the eclipsing accretion-powered millisecond X-ray pulsar SWIFT J1749.4-2807 in quiescence. Using the Chandra observation we derive a source position of Right Ascencion: 17:49:31.73 and Declination:-28:08:05.08. The position is accurate to 0.6" (90 per cent confidence). We find one source at a magnitude K=18.44+-0.03 with a position fully consistent with the accurate Chandra X-ray localization and a second source at K=19.2+-0.1 that falls close to the edge of the error circle in the deep K-band images. The presence of a few weaker sources as suggested by previous H-band observations presented in the literature cannot the ruled out. There is marginal evidence that the brighter of the these two sources is variable. Follow-up spectroscopy of this potential counterpart will show if this source is the true counterpart to SWIFT J1749.4-2807. If so, baring the presence of complicating effects such as heating of the mass-donor star, it would allow for the mass of the neutron star to be measured through the measurement of periodic radial velocity variations.