Radio modelling of the brightest and most luminous non-thermal colliding-wind binary Apep

Bloot, S.; Callingham, J. R.; Marcote, B.

doi:10.1093/mnras/stab2976

Cited by 5 publications

(12 citation statements)

References 57 publications

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“…In particular, by modelling the IR spiral plume, Han et al (2020) found the following orbital parameters for the Apep system: inclination i = 25 • ± 5 • , argument of periastron ω = 0 • ± 5 • , and true anomaly at 2018 epoch ν = −173 • ± 15 • . Similar values (within errors) were also obtained by Bloot et al (2021) by modelling the lightcurve at radio wavelengths. We can derive the corresponding projection angle for these parameters as ψ = arctan ( x 2 + y 2 /z), where x = D cos (ω − ν) cos (i), y = D sin (ω − ν), and z = D cos (ω − ν) sin (i) are the coordinates of the secondary star.…”

Section: Radio Emission Mapssupporting

confidence: 87%

“…Dougherty et al 2003). Thus, we expect that the actual impact of the wind anisotropies in the radio SED to be less significant than implied by Bloot et al (2021). With respect to the spherical wind approximation in our model, depending on the geometry of the system and the winds anisotropy, the anisotropy in the winds could potentially increase the opacity in the direction of the line of sight for photons coming from close to the bright apex of the WCR.…”

Section: Radio Spectral Energy Distributionmentioning

confidence: 89%

“…In any case, these observations proved unambiguously the presence of relativistic electrons accelerated at the WCR and the synchrotron nature of the radiation they produce. More recently, Bloot, Callingham, & Marcote (2021) presented a more complete dataset at radiofrequencies comprising observations with the uGMRT (at 255 and 583 MHz), ASKAP (at 887.5 MHz) and ATCA (at 1-3 GHz). These observations revealed that the source is variable on timescales of several years.…”

Section: Observations In the Radio Bandmentioning

confidence: 99%

“…Nonetheless, in this work, we do not aim to explore the radio variability due to the large uncertainties in the orbital parameters of Apep. For this reason, we only include in our forthcoming analysis the ATCA observations conducted in May 2017, and the uGMRT and ASKAP data obtained between 2018 and 2020 summarised in Bloot et al (2021). We also assume an additional 10% systematic error in flux density values due to calibration uncertainties.…”

Section: Observations In the Radio Bandmentioning

confidence: 99%

“…In addition, Callingham et al (2019) found observational evidence of anisotropy in the stellar winds, which is a feature not included in our model. Moreover, Bloot et al (2021) also favoured the presence of anisotropic winds in Apep by means of modelling the radio lightcurve using a one-zone approximation for the emitter. However, such a one-zone model treats the emitter as a point-like homogeneous region and is therefore incapable of accounting for the extended nature of the WCR and the fact that the emitted photons probe different regions of the stellar winds depending on their production site (e.g.…”

Section: Radio Spectral Energy Distributionmentioning

confidence: 99%

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The non-thermal emission from the colliding-wind binary Apep

Palacio

Benaglia

Becker

et al. 2022

Publ. Astron. Soc. Aust.

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Therecently discovered massive binary system Apep is the most powerful synchrotron emitter among the known Galactic colliding-wind binaries. This makes this particular system of great interest to investigate stellar winds and the non-thermal processes associated with their shocks. This source was detected at various radio bands, and in addition the wind-collision region was resolved by means of very-long baseline interferometric observations. We use a non-thermal emission model for colliding-wind binaries to derive physical properties of this system. The observed morphology in the resolved maps allows us to estimate the system projection angle on the sky to be $\psi \approx 85^\circ$ . The observed radio flux densities also allow us to characterise both the intrinsic synchrotron spectrum of the source and its modifications due to free–free absorption in the stellar winds at low frequencies; from this, we derive mass–loss rates of the stars of $\dot{M}_\mathrm{WN} \approx 4\times10^{-5}\;\mathrm{M}_\odot\,\mathrm{yr}^{-1}$ and $\dot{M}_\mathrm{WC} \approx 2.9\times10^{-5}\;\mathrm{M}_\odot\,\mathrm{yr}^{-1}$ . Finally, the broadband spectral energy distribution is calculated for different combinations of the remaining free parameters, namely the intensity of the magnetic field and the injected power in non-thermal particles. We show that the degeneracy of these two parameters can be solved with observations in the high-energy domain, most likely in the hard X-rays but also possibly in $\gamma$ -rays under favourable conditions.

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Section: Radio Emission Mapssupporting

confidence: 87%

Section: Radio Spectral Energy Distributionmentioning

confidence: 89%

Section: Observations In the Radio Bandmentioning

confidence: 99%

Section: Observations In the Radio Bandmentioning

confidence: 99%

Section: Radio Spectral Energy Distributionmentioning

confidence: 99%

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The non-thermal emission from the colliding-wind binary Apep

Palacio

Benaglia

Becker

et al. 2022

Publ. Astron. Soc. Aust.

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Limits on the non-thermal emission of the WR–WR system Apep

Martí-Devesa

Reimer

2023

A&A

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Colliding-wind binaries (CWBs) constitute an emerging class of γ-ray sources powered by strong, dense winds in massive stellar systems. The most powerful of them are those binaries hosting a Wolf-Rayet (WR) star. Following the recent discovery of Apep – the closest known Galactic WR–WR binary – we discuss the non-detection of its putative high-energy emission by the Fermi Large Area Telescope (Fermi-LAT) in this Letter. The limits reported in the GeV regime can be used to set a lower limit on the magnetic field pressure density within the shocked wind-collision region (WCR), and to exclude Apep as a bright γ-ray emitting binary. Given that this WR–WR system is the most luminous CWB identified until now at radio wavelengths, this result proves unambiguously that non-thermal synchrotron emission is not a suitable identifier for the subset of γ-ray emitters in this class of particle accelerators. Rather, Apep could be an interesting case of study for magnetic field amplification in shocked stellar winds.

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Evidence for non-thermal X-ray emission from the double Wolf-Rayet colliding-wind binary Apep

Palacio

García

Becker

et al. 2023

A&A

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Context. Massive colliding-wind binaries (CWBs) can be non-thermal sources. The emission produced in their wind-collision region (WCR) encodes information of both the shocks properties and the relativistic electrons accelerated in them. The recently discovered system Apep, a unique massive system hosting two Wolf-Rayet stars, is the most powerful synchrotron radio emitter among the known CWBs, being an exciting candidate to investigate the non-thermal processes associated with stellar wind shocks. Aims. We intend to break the degeneracy between the relativistic particle population and the magnetic field strength in the WCR of Apep by probing its hard X-ray spectrum, where inverse-Compton (IC) emission is expected to dominate. Methods. We observe Apep with NuSTAR for 60 ks and combine this with a re-analysis of a deep archival XMM-Newton observation to better constrain the X-ray spectrum. We use a non-thermal emission model to derive physical parameters from the results. Results. We detect hard X-ray emission consistent with a power-law component from Apep. This is compatible with IC emission produced in the WCR for a magnetic field of ≈ 105-190 mG, corresponding to a magnetic-to-thermal pressure ratio in the shocks of ≈ 0.007-0.021, and a fraction of ∼ 1.5 × 10 −4 of the total wind kinetic power being transferred to relativistic electrons. Conclusions. This is the first time that the non-thermal emission from a CWB is detected both in radio and high energies. This allows us to derive the most robust constraints of the particle acceleration efficiency and magnetic field intensity in a CWB so far, reducing the typical uncertainty of a few orders of magnitude to just within a factor of a few. This constitutes an important step forward in our characterisation of the physical properties of CWBs.

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Radio modelling of the brightest and most luminous non-thermal colliding-wind binary Apep

Cited by 5 publications

References 57 publications

The non-thermal emission from the colliding-wind binary Apep

The non-thermal emission from the colliding-wind binary Apep

Limits on the non-thermal emission of the WR–WR system Apep

Evidence for non-thermal X-ray emission from the double Wolf-Rayet colliding-wind binary Apep

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