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WR 140 is a long-period, highly eccentric Wolf-Rayet star binary system with exceptionally well-determined orbital and stellar parameters. Bright, variable X-ray emission is generated in shocks produced by the collision of the winds of the WC7pd+O5.5fc component stars. We discuss the variations in the context of the colliding-wind model using broad-band spectrometry from the RXTE, SWIFT, and NICER observatories obtained over 20 years and nearly 1000 observations through 3 consecutive 7.94-year orbits including 3 periastron passages. The X-ray luminosity varies as expected with the inverse of the stellar separation over most of the orbit: departures near periastron are produced when cooling shifts to excess optical emission in CIII $\lambda5696$ in particular. We use X-ray absorption to estimate mass-loss rates for both stars and to constrain the system morphology. The absorption maximum coincides closely with inferior conjunction of the WC star and provides evidence of the ion-reflection mechanism that underlies the formation of collisionless shocks governed by magnetic fields probably generated by the Weibel instability. Comparisons with K-band emission and HeI $\lambda$10830 absorption show that both are correlated after periastron with the asymmetric X-ray absorption. Dust appears within a few days of periastron suggesting formation within shocked gas near the stagnation point. X-ray flares seen in $\eta$ Carinae have not occurred in WR 140, suggesting the absence of large-scale wind inhomogeneities. Relatively constant soft emission revealed during the X-ray minimum is probably not from recombining plasma entrained in outflowing shocked gas., Comment: 52 pages, 17+1 figures, Accepted for publication in The Astrophysical Journal 23 August 2021

We quantify the rapid variations in X-ray brightness ("flares") from the extremely massive colliding wind binary Eta Carinae seen during the past three orbital cycles by RXTE. The observed flares tend to be shorter in duration and more frequent as periastron is approached, although the largest ones tend to be roughly constant in strength at all phases. Plausible scenarios include (1) the largest of multi-scale stochastic wind clumps from the LBV component entering and compressing the hard X-ray emitting wind-wind collision (WWC) zone, (2) large-scale corotating interacting regions in the LBV wind sweeping across the WWC zone, or (3) instabilities intrinsic to the WWC zone. The first one appears to be most consistent with the observations, requiring homologously expanding clumps as they propagate outward in the LBV wind and a turbulence-like power-law distribution of clumps, decreasing in number towards larger sizes, as seen in Wolf-Rayet winds.

We report X-ray measurements of nearly all known galactic Wolf-Rayet stars from the ROSAT all-sky survey and derive 0.2-2.4 keV luminosties.

New ROSAT PSPC and HRI observations of the Carina Nebula region are used to examine the X‐ray emission from the discrete sources as well as the diffuse hot gas in the Carina Nebula near Eta Carina. The spectral and spatial response of the PSPC allow analysis of the 0.1–2.4 keV spectra of all the bright point sources in the region and an examination of the spectral variation of the diffuse X‐rays. Analysis of the diffuse emission shows that most of the emission comes from gas at a temperature of a few million degrees, but also indicates the presence of hot (4E7 K) diffuse gas in an 11 pc region around Eta Car. Eta Car shows a 3 component spectrum with temperatures of 1E6 and 4E7 K. A 0.1×0.2 pc shell of X‐ray emitting gas around Eta Car has been resolved by the HRI, and comparison of the Einstein HRI and ROSAT HRI images supports the suggestion that the soft components originate in the shell (which is unresolved by the PSPC) while the hottest gas is produced less than an arcsec from the optical star. Spect...

The system parameters for the massive X-ray binary 4U 1700 - 37 are reexamined in the light of modern spectroscopic theory and new UV and X-ray data. The system is composed of HD 153919, an O6f star having a stronger wind, and an accreting neutron star. Revised parameters for the Of component are derived which are in accord with the parameters of single Of stars, which resolves the problem that 'the O star is undermassive by a factor of 2' formulated by Conti (1978). The ratio of the terminal velocity of the wind to the photospheric escape velocity agrees with those of O stars. The discrepancy between the values of the wind acceleration parameter, derived from X-ray and UV data, is resolved. The acceleration of the wind is similar to that of single OB star winds. It is suggested that the supernova explosion producing the neutron star in 4U 1700 - 37 occurred over a million years ago when HD 153919 was still on the main sequence.

Observations of the nova-like variable V Sge are discussed, and the ground-based light curve is analyzed, compensating for the component interaction effect. Low-dispersion IUE spectra indicate that interstellar reddening is smaller than suggested from visible-band observations. The UV and visible continuum are modeled by a He-rich model and by a simple accretion disk, and the UV spectrum emission lines are used to determine ionization temperatures and a lower N(e) limit. The present data are consistent with the picture of the companion to the He star being embedded in an accretion disk, with the disk being large (of dimension comparable to that of the embedding Roche lobe as a result of vigorous mass transfer) at the time of the ground-based data, and with the disk having been diminished to a radius of the order of 200 times of the neutron star, at the time of the IUE spectra.

During its first 2 years of operation, the gamma-ray AGILE satellite accumulated an extensive dataset for the Galactic plane. The data have been monitored for transient sources and several gamma-ray sources were detected. Their variability and possible association were studied. In this talk we will focus on the results of extensive observations of the Carina Region during the time period 2007 July - 2009 January, for a total livetime of ~130 days. The region is extremely complex, hosting massive star formation, with the remarkable colliding wind binary Eta Carinae, massive star clusters and HII regions (e.g. NGC 3324, RCW49, Westerlund II) and a giant molecular cloud extending over 150 pc (between l=284.7 and l=289). The Carina Nebula itself is the largest and IR highest surface brightness nebula of the Southern emisphere. We monitored several gamma ray sources in the Carina Region. In particular we detect a gamma ray source (1AGL J1043-5931) consistent with the position of Eta Carinae and report a remarkable 2-days gamma-ray flaring episode from this source on 2008 Oct 11-13. If 1AGL J1043-5931 is associated with the Eta Car system, our data provides the long sought first detection above 100 MeV of a colliding wind binary., 5 pages, 5 figures, proceedings of RICAP 2009

We present the results of extensive observations by the gamma-ray AGILE satellite of the Galactic region hosting the Carina nebula and the remarkable colliding wind binary Eta Carinae (Eta Car) during the period 2007 July to 2009 January. We detect a gamma-ray source (1AGL J1043-5931) consistent with the position of Eta Car. If 1AGL J1043-5931 is associated with the Eta Car system our data provide the long sought first detection above 100 MeV of a colliding wind binary. The average gamma-ray flux above 100 MeV and integrated over the pre-periastron period 2007 July to 2008 October is F = (37 +/- 5) x 10-8 ph cm-2 s-1 corresponding to an average gamma-ray luminosity of L = 3.4 x 10^34 erg s-1 for a distance of 2.3 kpc. We also report a 2-day gamma-ray flaring episode of 1AGL J1043-5931 on 2008 Oct. 11-13 possibly related to a transient acceleration and radiation episode of the strongly variable shock in the system., Comment: 5 pages, 4 figure, accepted for publication in ApJ Letters