HESS J0632+057 : A new gamma-ray binary?

TL;DR

HESS J0632+057 is a newly identified gamma-ray binary candidate, showing X-ray and TeV emissions, spectral variability, and spatial coincidence with a massive star, suggesting it belongs to a rare class of Galactic objects.

Contribution

This study presents evidence that HESS J0632+057 is a new gamma-ray binary, expanding the known population of such systems through multi-wavelength observations.

Findings

Coincidence of X-ray and TeV sources with a massive star

Hard X-ray spectrum with Gamma ~ 1.26

Significant variability on hour timescales

Abstract

The High Energy Stereoscopic System (HESS) survey of the Galactic plane has established the existence of a substantial number (~40) of Galactic TeV gamma-ray sources, a large fraction of which remain unidentified. HESS J0632+057 is one of a small fraction of these objects which is point-like in nature(<2' rms), and is one of only two point-like sources that remain unidentified. Follow-up observations of this object with XMM-Newton have revealed an X-ray source coincident with the TeV source and with the massive star MWC 148, of the spectral type B0pe. This source exhibits a hard spectrum, consistent with an absorbed power law with Gamma = 1.26 +/- 0.04, and shows significant variability on hour timescales. We discuss this spatial coincidence and the implied spectral energy distribution of this object and argue that it is likely a new gamma-ray binary system with a close resemblance to the three known members of this class, and in particular to LS I +61 303. Further X-ray, radio and optical observations of this system are needed to firmly establish HESS J0632+057 as a new member of this rare class of Galactic objects.