Spitzer IRAC observations of IR excess in Holmberg IX X-1: A circumbinary disk or a variable jet?

TL;DR

This study uses Spitzer IRAC data to identify an IR excess in Holmberg IX X-1, suggesting the presence of either a circumbinary disk or a variable jet, which cannot be explained by standard models.

Contribution

It provides the first IR observations of Holmberg IX X-1 and proposes a novel interpretation of the IR excess as dust emission from a circumbinary disk or jet.

Findings

Detected IR excess in the ULX SED

IR excess not explained by existing models

Suggests dust emission from circumbinary disk or jet

Abstract

We present Spitzer Infrared Array Camera (IRAC) photometric observations of the Ultra-luminous X-ray Source (ULX, X-1) in Holmberg IX. We construct a spectral energy distribution (SED) for Holmberg IX X-1 based on published optical, UV and X-ray data combined with the IR data from this analysis. We modeled the X-ray and optical data with disk and stellar models, however we find a clear IR excess in the ULX SED that cannot be explained by fits or extrapolations of any of these models. Instead, further analysis suggests that the IR excess results either from dust emission, possibly from a circumbinary disk or from a variable jet.