A New TeV Binary: The Discovery of an Orbital Period in HESS J0632+057

Abstract

HESS J0632+057 is a variable, point-like source of Very High Energy ($>100$ GeV) gamma-rays located in the Galactic plane. It is positionally coincident with a Be star, it is a variable radio and X-ray source, has a hard X-ray spectrum, and has low radio flux. These properties suggest that the object may be a member of the rare class of TeV/X-ray binary systems. The definitive confirmation of this would be the detection of a periodic orbital modulation of the flux at any wavelength. We have obtained {\it Swift} X-ray telescope observations of the source from MJD 54857 to 55647 (Jan. 2009 - Mar. 2011) to test the hypothesis that HESS J0632+057 is an X-ray/TeV binary. We show that these data exhibit flux modulation with a period of $321\pm 5$ days and we evaluate the significance of this period by calculating the null hypothesis probability, allowing for stochastic flaring. This periodicity establishes the binary nature of HESS J0632+057.

12 pages, 3 figures, accepted to ApJ Letters

References in corpus (6)

• VERITAS Observations of the gamma-Ray Binary LS I +61 303
• Discovery of a point-like very-high-energy gamma-ray source in Monoceros
• HESS J0632+057 : A new gamma-ray binary?
• Ten-year optical monitoring of PKS 0735+178: historical comparison, multiband behaviour and variability timescales
• Long-term X-ray monitoring of LS I +61 303: analysis of spectral variability and flares
• The TeV binary HESS J0632+057 in the low and high X-ray state

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• Highlights from VERITAS on VHE Gamma-ray Sources in our Galaxy
• NuSTAR Hard X-ray Observation of the Gamma-ray Binary Candidate HESS J1832-093
• Decade-long X-ray observations of HESS J0632+057
• Probing the Properties of the Pulsar Wind in the Gamma-Ray Binary HESS J0632+057 with NuSTAR and VERITAS Observations
• Observing the Energetic Universe at Very High Energies with the VERITAS Gamma Ray Observatory
• Multi-Wavelength Observation Campaign of the TeV Gamma-Ray Binary HESS J0632+057 with NuSTAR, VERITAS, MDM, and Swift
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• A Decade of TeV Observations of the Gamma-ray Binary HESSJ0632+057 with VERITAS
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• The Very Energetic Radiation Imaging Telescope Array System (VERITAS)