A spectral and spatial analysis of eta Carinae's diffuse X-ray emission using CHANDRA

Astronomisches Institut, Ruhr-Universität Bochum, 44780, Bochum, Germany; Astronomy Department, University of Minnesota, 55455, Minneapolis, MN, USA; Laboratory for High Energy Astrophysics, Goddard Space Flight Center, 20771, Greenbelt, MD, USA; Universities Space Research Association, Forbes Blvd, 7501, 20706, Seabrook, MD, USA
Astronomy and Astrophysics (Impact Factor: 4.48). 11/2003; DOI: 10.1051/0004-6361:20034306
Source: arXiv

ABSTRACT The luminous unstable star (star system) eta Carinae is surrounded by an optically bright bipolar nebula, the Homunculus and a fainter but much larger nebula, the so-called outer ejecta. As images from the EINSTEIN and ROSAT satellites have shown, the outer ejecta is also visible in soft X-rays, while the central source is present in the harder X-ray bands. With our CHANDRA observations we show that the morphology and properties of the X-ray nebula are the result of shocks from fast clumps in the outer ejecta moving into a pre-existing denser circumstellar medium. An additional contribution to the soft X-ray flux results from mutual interactions of clumps within the ejecta. Spectra extracted from the CHANDRA data yield gas temperatures kT of 0.6-0.76 keV. The implied pre-shock velocities of 670-760 km/s are within the scatter of the velocities we measure for the majority of the clumps in the corresponding regions. Significant nitrogen enhancements over solar abundances are needed for acceptable fits in all parts of the outer ejecta, consistent with CNO processed material and non-uniform enhancement. The presence of a diffuse spot of hard X-ray emission at the S condensation shows some contribution of the highest velocity clumps and further underlines the multicomponent, non-equilibrium nature of the X-ray nebula. The detection of an X-ray ``bridge'' between the northern and southern part of the X-ray nebula and an X-ray shadow at the position of the NN bow can be attributed to a large expanding disk, which would appear as an extension of the equatorial disk. No soft emission is seen from the Homunculus, or from the NN bow or the ``strings''. Comment: 15 pages, 10 figures, accepted by A&A; paper including images with full resolution available at

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    ABSTRACT: Eta Carinae is the colliding wind binary with the largest mass loss rate in our Galaxy and the only one in which hard X-ray emission has been detected. Eta Carinae is therefore a primary candidate to search for particle acceleration by probing its gamma-ray emission. 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. A bright gamma-ray source is detected at the position of eta Carinae. Its flux at a few 100 MeV corresponds very well to the extrapolation of the hard X-ray spectrum towards higher energies. The spectral energy distribution features two distinct components. The first one extends over 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 gamma~1E4 in the colliding wind region. The expected synchrotron emission is compatible with the existing upper limit on the non-thermal radio emission. The second component is a hard gamma-ray tail detected above 20 GeV. It could be explained by pi0-decay of accelerated hadrons interacting with the dense stellar wind. The ratio between the fluxes of the pi0 and 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. We have measured the electron spectrum responsible for the keV to GeV emission and detected an evidence of hadronic acceleration in eta Carinae. These observations are thus in good agreement with the colliding wind scenario suggested for eta Carinae. Comment: 7 pages, 5 figures
    Astronomy and Astrophysics 08/2010; · 4.48 Impact Factor
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    ABSTRACT: We present integral field spectroscopy of the Homunculus nebula aroundCarinae in the near-infrared window (J band), encompassing spectral lines sensitive to shocks and photo-ionisation. We use the [Fe ii] 12567/Pa ratio to trace the regions excited by collisions and the He I 10830 line to map photo-excitation. We report the de- tection of a hole in both lobes near the pole and use a cylindrical model to match the observations and then determine the thickness of the lobes at the polar region (R=6.5 × 1016 cm) and the radius of the holes (2025 A.U.). We map the blue-shifted beamed component seen in the He I 10830 as an intrinsic emission in front of the NW lobe and conclude that it is formed by the UV photoexcitation escaping directly from the Purple Haze as it extends to outside the limits of the lobes and do not seems to lay on the equatorial disc. Our velocity maps reveal that the spatial distribution of the Little Homunculus is coincident with the radio continuum emission at 3 cm, indicating that it is a photon-bounded H II region. We take advantage of this to constrain the luminosity of the secondary star in the system showing that a lower limit for the luminosity corresponds to an O7I or WNha star. We confirm previous findings of structures inside and outside of the Homunculus, produce a more complete view of them and bring to light new features.
    Monthly Notices of the Royal Astronomical Society 06/2008; 387(2):564. · 5.52 Impact Factor
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    ABSTRACT: η Carinae is surrounded by a complex circumstellar nebula ejected during more than one eruption, the great eruption in the 1840s and the second or lesser eruption in the 1890s. Beyond the well-defined edges of its famous bipolar nebula are additional nebulous features and ejecta referred to as the outer ejecta. The outer ejecta includes a variety of structures of very different sizes and morphologies distributed in a region 0.67 pc in diameter with a mass of > 2-4 M⊙. Some individual features in the outer ejecta are moving extremely fast, up to 3,200 km/s, with most of the expansion velocities between 400-900 km/s. As a consequence of these high velocities, structures in the outer ejecta interact with the surrounding medium and with each other. The strong shocks that arise from these interactions give rise to soft X-ray emission. The global expansion pattern of the outer ejecta reveals an overall bipolar distribution, giving a symmetric structure to its morphologically more irregular appearance. The long, highly collimated filaments, called strings, are particularly unusual. The material in the strings follow a Hubble-flow and appear to originate at the central star. The properties of the nebulae associated with other LBVs also are described and compared with η Car. HR Car and AG Car show similar bipolar morphologies but are much older; HR Car's nebula may be η Car's older twin. The larger, extended nebulae detected around the giant eruption LBV P Cygni, and the extended nebulosity associated with AG Car and HR Car could be either from previous eruptions or facsimiles to η Car's outer ejecta.

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