The high energy X-ray tail of $\mathsf{\eta}$ Car revealed by BeppoSAX

Viotti, R.; Antonelli, L. A.; Rossi, C.; Rebecchi, S.

doi:10.1051/0004-6361:20040113

Cited by 28 publications

(46 citation statements)

References 27 publications

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“…A hard X-ray tail had first been observed towards η Carinae by BeppoSAX (Viotti et al 2004), and subsequently unambiguously confirmed by both INTEGRAL (Leyder et al 2008(Leyder et al , 2010 and Suzaku (Sekiguchi et al 2009) observations. This provides a strong evidence that the wind collision leads to non-thermal electron acceleration, and suggests the possibility of a gammaray detection.…”

Section: Introductionmentioning

confidence: 73%

ηCarinae: a very large hadron collider

Farnier

Walter

Leyder

2010

A&A

109

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Context. η Carinae is the colliding wind binary with the highest mass-loss rate in our Galaxy and the only one in which hard X-ray emission has been detected. Aims. η Carinae is therefore a primary candidate to search for particle acceleration by probing its gamma-ray emission. Methods. We used the first 21 months of Fermi/LAT data to extract gamma-ray (0.2-100 GeV) images, spectra, and light-curves, then combined them with multi-wavelength observations to model the non-thermal spectral energy distribution. Results. A bright gamma-ray source is detected at the position of η Carinae. Its flux at a few 100 MeV can be modelled by an extrapolation of the hard X-ray spectrum towards higher energies. The spectral energy distribution features two distinct components. The first one extends from the keV to GeV energy range, and features an exponential cutoff at ∼1 GeV. It can be understood as inverse Compton scattering of ultraviolet photons by electrons accelerated up to γ ∼ 10 4 in the colliding wind region. The expected synchrotron emission is compatible with the existing upper limit to the non-thermal radio emission. The second component is a hard gamma-ray tail detected above 20 GeV. It could be explained by π 0 -decay of accelerated hadrons interacting with the dense stellar wind. The ratio of the fluxes of the π 0 to inverse Compton components is roughly as predicted by simulations of colliding wind binaries. This hard gamma-ray tail can only be understood if emitted close to the wind collision region. The energy transferred to the accelerated particles (∼5% of the collision mechanical energy) is comparable to that of the thermal X-ray emission. Conclusions. The electron spectrum responsible for the keV to GeV emission was modelled and the observed emission above 20 GeV strongly suggests hadronic acceleration in η Carinae. These observations are thus in good agreement with the colliding wind scenario proposed for η Carinae.

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Section: Introductionmentioning

confidence: 73%

ηCarinae: a very large hadron collider

Farnier

Walter

Leyder

2010

A&A

109

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“…The unfolded model is the magenta long-dashed line; with the thermal and non-thermal components respectively shown by the dotted dark blue and light blue lines. Viotti et al 2004); this however does not affect the values derived for the photon index. The unfolded spectrum outside periastron is shown in Fig.…”

Section: Fig 3 Bepposax/mecs (Black) and Integral/isgrimentioning

confidence: 98%

“…A hard X-ray tail (i.e., at a flux higher than an extrapolation of the thermal X-ray component η HX) was once detected in the η Car region by the PDS instrument onboard BeppoSAX (Viotti et al 2004). Since then, it was unambiguously confirmed by INTEGRAL (Leyder et al 2008), and reobserved by Suzaku (Sekiguchi et al 2009).…”

Section: X-ray Observationsmentioning

confidence: 99%

Hard X-ray identification ofη Carinae and steadiness close to periastron

Leyder¹,

Walter²,

Rauw³

2010

A&A

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Context. The colliding-wind binary η Carinae exhibits soft X-ray thermal emission that varies strongly around the periastron passage. It has been found to have non-thermal emission, thanks to its detection in hard X-rays using INTEGRAL and Suzaku, and also in γ-rays with AGILE and Fermi. Aims. This paper attempts to definitively identify η Carinae as the source of the hard X-ray emission, to examine how changes in the 2-10 keV band influence changes in the hard X-ray band, and to understand more clearly the mechanisms producing the non-thermal emission using new INTEGRAL observations obtained close to periastron passage. Methods. To strengthen the identification of η Carinae with the hard X-ray source, a long Chandra observation encompassing the INTEGRAL/ISGRI error circle was analysed, and all other soft X-ray sources (including the outer shell of η Carinae itself) were discarded as likely counter-parts. To expand the knowledge of the physical processes governing the X-ray lightcurve, new hard X-ray images of η Carinae were studied close to periastron, and compared to previous observations far from periastron. Results. The INTEGRAL component, when represented by a power law (with a photon index Γ of 1.8), would produce more emission in the Chandra band than observed from any point source in the ISGRI error circle apart from η Carinae, as long as the hydrogen column density to the ISGRI source is lower than N H 10 24 cm −2 . Sources with such a high absorption are very rare, thus the hard X-ray emission is very likely to be associated with η Carinae. The eventual contribution of the outer shell to the non-thermal component also remains fairly limited. Close to periastron passage, a 3-σ detection is achieved for the hard X-ray emission of η Carinae, with a flux similar to the average value far from periastron. Conclusions. Assuming a single absorption component for both the thermal and non-thermal sources, this 3-σ detection can be explained with a hydrogen column density that does not exceed N H 6 × 10 23 cm −2 without resorting to an intrinsic increase in the hard X-ray emission. The energy injected in hard X-rays (averaged over a month timescale) appears to be rather constant at least as close as a few stellar radii, well within the acceleration region of the wind.

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“…They produce synchrotron radiation with the spectral index α e ± syn = 2. The spectral index of the hard X-ray emission from the Eta Carinae binary system is not precisely known (Viotti et al 2004;Leyder et al 2008Leyder et al , 2010Sekiguchi et al 2009). However, it is reported to be not far from the above value.…”

Section: Model Bmentioning

confidence: 99%

High-energy radiation from the massive binary system Eta Carinae

Bednarek

Pabich

2011

A&A

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Context. The most massive binary system Eta Carinae has been recently established as a gamma-ray source by the AGILE and Fermi-LAT detectors. The high energy spectrum of this gamma-ray source is very intriguing. It shows two clear components and a lack of any evidence of variability with the orbital period of the binary system. Aims. We consider different scenarios for the acceleration of particles (both electrons and hadrons) and the production of the high energy radiation in the model of stellar wind collisions within the binary system Eta Carinae with the aim to explain the gamma-ray observations and predict the behaviour of the source at very high gamma-ray energies. Methods. The gamma-ray spectra calculated in terms of the specific models are compared with the observations of Eta Carinae, and the neutrino spectra produced in hadronic models are confronted with the atmospheric neutrino background and the sensitivity of 1 km 2 neutrino telescope. Results. We show that spectral features can be explained in terms of the stellar wind collision model between the winds of the companion stars in which the acceleration of particles occurs on both sides of the double shock structure. The shocks from the Eta Carinae star and the companion star can accelerate particles to different energies depending on the different conditions determined by the parameters of the stars. The lack of strong GeV gamma-ray variability with the period of the binary system can be also understood in terms of such a model. Conclusions. We predict that the gamma-ray emission features at energies above ∼100 GeV will show significant variability (or its lack) depending on the acceleration and interaction scenario of particles accelerated within the binary system. For the hadronic models we predict the expected range of neutrino fluxes from the binary system Eta Carinae. This can be tested through observations with the large-scale neutrino telescopes, which will support or disprove the specific hadronic models.

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The high energy X-ray tail of $\mathsf{\eta}$ Car revealed by BeppoSAX

Cited by 28 publications

References 27 publications

ηCarinae: a very large hadron collider

ηCarinae: a very large hadron collider

Hard X-ray identification ofη Carinae and steadiness close to periastron

High-energy radiation from the massive binary system Eta Carinae

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