Outstanding X-ray emission from the stellar radio pulsar CU Virginis

Robrade, J.; Oskinova, L. M.; Schmitt, J. H. M. M.; Leto, P.; Trigilio, C.

doi:10.1051/0004-6361/201833492

Cited by 17 publications

(19 citation statements)

References 24 publications

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“…The presence of non thermal X-ray photons is not a unique prerogative of the early B magnetic stars. The cooler star CU Vir (T eff ≈ 13 kK) also has an X-ray spectrum compatible with the presence of a non-thermal component (Robrade et al 2018).…”

Section: Discussionmentioning

confidence: 94%

“…Stellar ARE from early-type magnetic stars was detected as wide band strongly circularly polarized radio pulses arising from auroral rings above the magnetic poles (Trigilio et al 2011). While the auroral signature in the UV spectrum of the prototypical star CU Vir was not found (Krtička et al 2019), the search in X-rays gives promising results (Robrade et al 2018).…”

Section: Introductionmentioning

confidence: 99%

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Evidence for radio and X-ray auroral emissions from the magnetic B-type star ρ Oph A

Leto

Trigilio

Leone³

et al. 2020

Monthly Notices of the Royal Astronomical Society

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We present new ATCA multi-wavelength radio measurements (range 2.1-21.2 GHz) of the early-type magnetic star ρ Oph A, performed in March 2019 during 3 different observing sessions. These new ATCA observations evidence a clear rotational modulation of the stellar radio emission and the detection of coherent auroral radio emission from ρ Oph A at 2.1 GHz. We collected high-resolution optical spectra of ρ Oph A acquired by several instruments over a time span of about ten years. We also report new magnetic field measurements of ρ Oph A that, together with the radio light curves and the temporal variation of the equivalent width of the He I line (λ = 5015Å), were used to constrain the rotation period and the stellar magnetic field geometry. The above results have been used to model the stellar radio emission, modelling that allowed us to constrain the physical condition of ρ Oph A's magnetosphere. Past XMM-Newton measurements showed periodic X-ray pulses from ρ Oph A. We correlate the X-ray light curve with the magnetic field geometry of ρ Oph A. The already published XMM-Newton data have been re-analyzed showing that the X-ray spectra of ρ Oph A are compatible with the presence of a non-thermal X-ray component. We discuss a scenario where the emission phenomena occurring at the extremes of the electromagnetic spectrum, radio and X-ray, are directly induced by the same plasma process. We interpret the observed X-ray and radio features of ρ Oph A as having an auroral origin.

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Section: Discussionmentioning

confidence: 94%

Section: Introductionmentioning

confidence: 99%

Evidence for radio and X-ray auroral emissions from the magnetic B-type star ρ Oph A

Leto

Trigilio

Leone³

et al. 2020

Monthly Notices of the Royal Astronomical Society

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“…Recently, radio studies of strongly magnetic chemically peculiar Bp stars revealed a variable polarimetric behavior and radio continua consistent with nonthermal processes resulting from auroral mechanisms (e.g., Leto et al 2017Leto et al , 2018Leto et al , 2020. Robrade et al (2018) suggested that the auroral mechanisms also operate in strongly magnetic Ap stars, such as CU Vir, which is detected in X-rays with L X ≈ 3 × 10 28 erg s −1 and has hard X-ray emissions with T X ≈ 25 K.…”

Section: Introductionmentioning

confidence: 89%

“…Recent improvements in the MCWS models account for the auroral emission, and are capable of explaining jointly radio and X-ray observations of magnetic B2Vp stars (Leto et al 2017(Leto et al , 2020). The auroral model was also successfully applied to the Ap star CU Vir (Robrade et al 2018). However, there are principal differences between CU Vir and KQ Vel.…”

Section: Auroral X-ray Emission Of a Magnetic Ap Starmentioning

confidence: 99%

Chandra X-ray study confirms that the magnetic standard Ap star KQ Vel hosts a neutron star companion

Oskinova

Ignace

Leto

et al. 2020

A&A

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Context. KQ Vel is a peculiar A0p star with a strong surface magnetic field of about 7.5 kG. It has a slow rotational period of nearly 8 years. Bailey et al. (A&A, 575, A115) detected a binary companion of uncertain nature and suggested that it might be a neutron star or a black hole. Aims. We analyze X-ray data obtained by the Chandra telescope to ascertain information about the stellar magnetic field and/or interaction between the star and its companion. Methods. We confirm previous X-ray detections of KQ Vel with a relatively high X-ray luminosity of 2 × 1030 erg s−1. The X-ray spectra suggest the presence of hot gas at > 20 MK and, possibly, of a nonthermal component. The X-ray light curves are variable, but data with better quality are needed to determine a periodicity, if any. Results. We interpret the X-ray spectra as a combination of two components: the nonthermal emission arising from the aurora on the A0p star, and the hot thermal plasma filling the extended shell that surrounds the “propelling” neutron star. Conclusions. We explore various alternatives, but a hybrid model involving the stellar magnetosphere along with a hot shell around the propelling neutron star seems most plausible. We speculate that KQ Vel was originally a triple system and that the Ap star is a merger product. We conclude that KQ Vel is an intermediate-mass binary consisting of a strongly magnetic main-sequence star and a neutron star.

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“…Magnetic Ap/Bp stars are also X-ray emitters via magnetically confined wind shocks (MCWS; Babel & Montmerle 1997) and their magnetosphere might even generate nonthermal X-rays via auroral emission (Leto et al 2017). An application of this model to the A0p star CU Vir is presented in Robrade et al (2018) and while its spectral X-ray characteristics are comparable to those of HD 94660, its X-ray luminosity is about two orders of magnitudes lower. Although the magnetospheres of the two stars differ due to the higher magnetic field and the slower rotation of HD 94660, log L X > 30 is above what is typically observed for comparable stars.…”

Section: X-ray Emissionmentioning

confidence: 99%

The near-infrared companion to HD 94660 (=KQ Vel)

Schöller

Hummel

Hubrig

et al. 2020

A&A

Self Cite

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Context. The Bp star HD 94660 is a single-lined spectroscopic binary. Some authors have suggested that the unseen companion of at least 2 M⊙ may be a compact object. Aims. We intend to study this multiple system in detail, especially to learn more about the thus far unseen companion. Methods. We have collected and analyzed PIONIER (Precision Integrated-Optics Near-infrared Imaging ExpeRiment) H-band data from the Very Large Telescope Interferometer, TESS (Transiting Exoplanet Survey Satellite) visible photometric data, and X-ray observations with Chandra of HD 94660. Results. Using PIONIER, we were able to detect the companion to HD 94660, which is absent from high quality spectra at visible wavelengths, with a magnitude difference of 1.8 in the H band at a separation of 18.72 mas. The TESS light curve shows variations with a period of 2.1 d and also flaring. The Chandra spectrum is well described by emission from hot thermal plasma, yet it might include a nonthermal component. The X-ray properties are compatible with a magnetically active companion, while it is also possible that there might be some magnetospheric contributions from the primary. Conclusions. We can rule out that the companion to HD 94660 is a compact source. It is also very unlikely that this companion is a single star, as the estimated mass of more than 2 M⊙, the magnitude difference of 1.8 in the H band, and its nondetection in visible spectra are difficult to realize in a single object. One alternative could be a pair of late F stars, which would also be responsible for the detected photometric variations. Interferometric observations over the full binary orbit are necessary to determine the real mass of the companion and to add constraints on the overall geometry of the system.

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Outstanding X-ray emission from the stellar radio pulsar CU Virginis

Cited by 17 publications

References 24 publications

Evidence for radio and X-ray auroral emissions from the magnetic B-type star ρ Oph A

Evidence for radio and X-ray auroral emissions from the magnetic B-type star ρ Oph A

Chandra X-ray study confirms that the magnetic standard Ap star KQ Vel hosts a neutron star companion

The near-infrared companion to HD 94660 (=KQ Vel)

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