Optical and Near-Infrared Monitoring of Gamma-ray Binaries Hosting Be Stars

Moritani, Yuki; Kawachi, A.

doi:10.3390/universe7090320

Cited by 4 publications

(5 citation statements)

References 41 publications

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“…The orbital motion of the compact object is expected to produce orbital modulation in the circumstellar disc. A summary of the observed orbital variations in three Be/ γ ‐ray binaries is given in Moritani & Kawachi (2021). To search for signatures of the orbital modulation of the emission lines formed in the Be disc, we conducted a periodogram analysis of the measured emission line parameters (see Section 2) using the phase dispersion minimization, PDM (Stellingwerf 1978), Lomb‐Scargle (Lomb 1976; Scargle 1982) and CLEAN (Roberts et al 1987) algorithms.…”

Section: Resultsmentioning

confidence: 99%

Optical spectroscopy of the Be/black hole binary MWC 656 ‐ interaction of a black hole with a circumstellar disc

et al. 2022

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We present new spectroscopic observations of the Be/black hole binary MWC 656 obtained during the period 2015–2021. We measure the equivalent width of Hα (EWα), Hβ (EWβ$$ {EW}_{\beta } $$), and the distance between the peaks of Hα (normalΔVα$$ \Delta {V}_{\alpha } $$), Hβ (normalΔVβ$$ \Delta {V}_{\beta } $$), and FeII (normalΔVFeII$$ \Delta {V}_{\mathrm{FeII}} $$) lines. Combining new and old data, we find that: (1) the density of the circumstellar disc of MWC 656 (normalΔVα$$ \Delta {V}_{\alpha } $$ versus EWα$$ {EW}_{\alpha } $$ diagram) is similar to the Be stars. For the Be stars, we find the relation normalΔVβ=0.999normalΔVα+62.4$$ \Delta {V}_{\beta }=0.999\Delta {V}_{\alpha }+62.4 $$ km s−1, and the position of MWC 656 corresponds to the average behavior of the Be stars. This means that the presence of the black hole does not change the overall structure of the circumstellar disc; (2) the periodogram analysis indicates modulation of EWα$$ {EW}_{\alpha } $$ with a period 60.4±0.4$$ 60.4\pm 0.4 $$ days, which is identical to the binary orbital period. The maxima of EWα$$ {EW}_{\alpha } $$ and EWβ$$ {EW}_{\beta } $$ are around periastron (phase zero); (3) around orbital phase zero, normalΔVβ$$ \Delta {V}_{\beta } $$ and normalΔVFeII$$ \Delta {V}_{FeII} $$ decrease by about 30$$ 30 $$ km s−1. This suggests that we observe an increase of the circumstellar disc size induced by the periastron passage of the black hole and that the entire circumstellar disc pulsates with the orbital period with relative amplitude of 10–20%. The observations also indicate, that the reason for the black hole in MWC 656 to be in deep quiescence is a very low efficiency of accretion (∼2×10−6$$ \sim 2\times {10}^{-6} $$).

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Section: Resultsmentioning

confidence: 99%

Optical spectroscopy of the Be/black hole binary MWC 656 ‐ interaction of a black hole with a circumstellar disc

et al. 2022

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“…Be/γ-ray binaries provide information as to the relationship between Be stars and high-energy astrophysics (Lamberts 2016;Moritani & Kawachi 2021). Interaction between these compact objects and their stellar outflow is believed to play an essential role in shaping their multi-wavelength light curves.…”

Section: Discussionmentioning

confidence: 99%

Modelling the correlated keV/TeV light curves of Be/gamma-ray binaries

Chen

Takata

2022

A&A

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Be/γ-ray binaries comprise a confirmed or presumptive pulsar orbiting a Be star and emit luminous γ-rays. Non-thermal emissions are thought to arise from synchrotron radiation and inverse-Compton (IC) scattering in the shock where the pulsar wind is terminated by the stellar outflow. We study wind interactions and shock radiations from such systems and show that the bimodal structures observed in keV/TeV light curves are caused by enhanced synchrotron radiation and IC scattering during disc passages. We use a simple radiation model to reproduce orbital modulations of keV X-ray and TeV γ-ray flux and compare with two confirmed pulsar/Be star binaries (i.e. PSR B1259-63/LS 2883 and PSR J2032+4127/MT91 213), and two candidates (i.e. HESS J0632+057 and LS I +61°303). We find that the keV/TeV light curves of the former two binaries can be well explained by the inclined disc model, while modelling the modulated emissions of the latter two sources remains challenging with current orbital solutions. Therefore, we propose alternative orbital geometries for HESS J0632+057 and LS I +61°303. We estimate the positions and inclination angles of Be discs by fitting correlated keV/TeV light curves. Our results could be beneficial for future measurements of orbital parameters and searches for radio pulsations from presumed pulsars.

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“…The average of the magnitude difference of the comparison stars is subtracted in order to remove a noise from the instrument instabilities. For the same reason not only the statistical error of the target, but also the standard deviation of the comparison stars are included to calculate the error of each observation [see Moritani and Kawachi (2021) for details].…”

Section: Data Reduction and Light Curve Analysismentioning

confidence: 99%

“…We have been monitoring LS 5039 and 1FGL J1018.6−5856 in the near-infrared (JHKs) band as a monitoring campaign of several gamma-ray binaries to search for the orbital modulation associated with the massive star and circumstellar materials (Kawachi et al 2021;Moritani and Kawachi 2021). The near-infrared flux may change at different orbital phases if the optical depth in the lineof-sight varies significantly across the orbit.…”

Section: Introductionmentioning

confidence: 99%

Novel application to estimate the mass-loss and the dust-formation rates in O-type gamma-ray binaries using near-infrared photometry

Moritani

Kawachi

Okazaki

et al. 2023

Publications of the Astronomical Society of Japan

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We have performed the near-infrared photometric monitoring observations of two TeV gamma-ray binaries with O-stars (LS 5039 and 1FGL J1018.6−5856), using IRSF/SIRIUS at SAAO, in order to study the stellar parameters and their perturbations caused by the binary interactions. The whole orbital phase was observed multiple times and no significant variabilities including orbital modulations were detected for both targets. Assuming that the two systems are colliding wind binaries, we estimate the amplitude of flux variation caused by the difference in the optical depth of O-star wind at inferior conjunction, where the star is seen through the cavity created by pulsar wind, and other orbital phases without pulsar-wind intervention. The derived amplitude is <0.001 mag, which is about two orders of magnitude smaller than the observed upper limit. Also using the upper limits of the near-infrared variability, we for the first time obtain the upper limit of the dust formation rate resulting from wind–wind collision in O-star gamma-ray binaries.

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Optical and Near-Infrared Monitoring of Gamma-ray Binaries Hosting Be Stars

Cited by 4 publications

References 41 publications

Optical spectroscopy of the Be/black hole binary MWC 656 ‐ interaction of a black hole with a circumstellar disc

Optical spectroscopy of the Be/black hole binary MWC 656 ‐ interaction of a black hole with a circumstellar disc

Modelling the correlated keV/TeV light curves of Be/gamma-ray binaries

Novel application to estimate the mass-loss and the dust-formation rates in O-type gamma-ray binaries using near-infrared photometry

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