Evidence for long-term Gamma-ray and X-ray variability from the unidentified TeV source HESS J0632+057

TL;DR

This study presents long-term gamma-ray and X-ray observations of HESS J0632+057, providing evidence of variability that supports its classification as a gamma-ray binary system, despite non-detections in gamma rays during certain periods.

Contribution

The paper provides the first long-term variability analysis of HESS J0632+057 in gamma-ray and X-ray bands, strengthening its identification as a gamma-ray binary.

Findings

No significant gamma-ray signal detected above 1 TeV in 2006, 2008, 2009.

Gamma-ray flux is variable, with non-steady emission confirmed.

X-ray flux increased by a factor of 1.8, indicating variability.

Abstract

HESS J0632+057 is one of only two unidentified very-high-energy gamma-ray sources which appear to be point-like within experimental resolution. It is possibly associated with the massive Be star MWC 148 and has been suggested to resemble known TeV binary systems like LS I +61 303 or LS 5039. HESS J0632+057 was observed by VERITAS for 31 hours in 2006, 2008 and 2009. During these observations, no significant signal in gamma rays with energies above 1 TeV was detected from the direction of HESS J0632+057. A flux upper limit corresponding to 1.1% of the flux of the Crab Nebula has been derived from the VERITAS data. The non-detection by VERITAS excludes with a probability of 99.993% that HESS J0632+057 is a steady gamma-ray emitter. Contemporaneous X-ray observations with Swift XRT reveal a factor of 1.8+-0.4 higher flux in the 1-10 keV range than earlier X-ray observations of HESS J0632+057. The variability in the gamma-ray and X-ray fluxes supports interpretation of the ob ject as a gamma-ray emitting binary.