Probing the nature of the TeV gamma-ray binary HESS J0632+057 by monitoring Be disk variability

Abstract

We report on monitoring observations of the TeV gamma-ray binary HESS J0632+057, which were carried out to constrain the interaction between the Be circumstellar disk and the compact object of unknown nature, and provide for the first time high-dispersion (R > 50000) optical spectra in the second half of the orbital cycle, from apastron through periastron. The Halpha, Hbeta, and Hgamma line profiles are found to exhibit remarkable short-term variability for ~1 month after the apastron (phase 0.6--0.7), whereas they show little variation near the periastron. These emission lines show "S-shaped" variations with timescale of ~150 days, which is about twice that reported previously. In contrast to the Balmer lines, no profile variability is seen in any FeII emission line. We estimate the radii of emitting regions of the Halpha, Hbeta, Hgamma, and FeII emission lines to be ~30, 11, 7, and 2 stellar radii (R_*), respectively. The amplitudes of the line profile variations in different lines indicate that the interaction with the compact object affects the Be disk down to, at least, the radius of 7 R_* after the apastron. This fact, together with little profile variability near the periastron, rules out the tidal force as the major cause of disk variability. Although this leaves the pulsar wind as the most likely candidate mechanism for disk variations, understanding the details of the interaction, particularly the mechanism for causing a large-scale disk disturbance after the apastron, remains an open question.

arXiv comment20 pages, 4 figures, accepted to ApJ Letter

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Cited by in corpus (13)

• Modelling Jets, Tori and Flares in Pulsar Wind Nebulae
• Overview of non-transient gamma-ray binaries and prospects for the Cherenkov Telescope Array
• Observation of the gamma-ray binary HESS J0632+057 with the H.E.S.S., MAGIC, and VERITAS telescopes
• Orbital solution leading to an acceptable interpretation for the enigmatic gamma-ray binary HESS J0632+057
• Optical spectroscopy of Be/gamma-ray binaries
• Very high energy Fermi/LAT detection of HESS J0632+057
• 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
• Investigation of the broadband emission of the gamma-ray binary HESS J0632+057 using an intrabinary shock model
• Multi-Wavelength Observation Campaign of the TeV Gamma-Ray Binary HESS J0632+057 with NuSTAR, VERITAS, MDM, and Swift
• Modeling the GeV emission of HESS J0632+057
• Optical and Near-Infrared Monitoring of Gamma-ray Binaries Hosting Be Stars
• First multicolour polarimetry of TeV gamma-ray binary HESS J0632+057 close to periastron passage