New millisecond pulsars (MSPs) in compact binaries provide a good opportunity to search for the most massive neutron stars. Their main-sequence companion stars are often strongly irradiated by the pulsar, displacing the effective center of light from their barycenter and making mass measurements uncertain. We present a series of optical spectroscopic and photometric observations of PSRJ2215+5135, a "redback" binary MSP in a 4.14hr orbit, and measure a drastic temperature contrast between the dark/cold (T N =5660 -+ 380470 K) sides of the companion star. We find that the radial velocities depend systematically on the atmospheric absorption lines used to measure them. Namely, the semi-amplitude of the radial velocity curve (RVC) of J2215 measured with magnesium triplet lines is systematically higher than that measured with hydrogen Balmer lines, by 10%. We interpret this as a consequence of strong irradiation, whereby metallic lines dominate the dark side of the companion (which moves faster) and Balmer lines trace its bright (slower) side. Further, using a physical model of an irradiated star to fit simultaneously the two-species RVCs and the three-band light curves, we find a center-of-mass velocity of K 2 =412.3±5.0 km s −1 and an orbital inclination i=63°.

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In X-ray binaries, compact jets are known to commonly radiate at radio to infrared frequencies, whereas at optical to γ-ray energies, the contribution of the jet is debated. The total luminosity, and hence power of the jet is critically dependent on the position of the break in its spectrum, between optically thick (self-absorbed) and optically thin synchrotron emission. This break, or turnover, has been reported in just one black hole X-ray binary (BHXB) thus far, GX 339-4, and inferred via spectral fitting in two others, A0620-00 and Cyg X-1. Here, we collect a wealth of multiwavelength data from the outbursts of BHXBs during hard X-ray states, in order to search for jet breaks as yet unidentified in their spectral energy distributions. In particular, we report the direct detection of the jet break in the spectrum of V404 Cyg during its 1989 outburst, at ν b = (1.8 ± 0.3) × 10 14 Hz (1.7 ± 0.2µm). We increase the number of BHXBs with measured jet breaks from three to eight. Jet breaks are found at frequencies spanning more than two orders of magnitude, from ν b = (4.5 ± 0.8) × 10 12 Hz for XTE J1118+480 during its 2005 outburst, to ν b > 4.7 × 10 14 Hz for V4641 Sgr in outburst. A positive correlation between jet break frequency and luminosity is expected theoretically; ν b ∝ L ∼0.5 ν,jet if other parameters are constant. With constraints on the jet break in a total of 12 BHXBs including two quiescent systems, we find a large range of jet break frequencies at similar luminosities and no obvious global relation (but such a relation cannot be ruled out for individual sources). We speculate that different magnetic field strengths and/or different radii of the acceleration zone in the inner regions of the jet are likely to be responsible for the observed scatter between sources. There is evidence that the high energy cooling break in the jet spectrum shifts from UV energies at L X ∼ 10 −8 L Edd (implying the jet may dominate the Xray emission in quiescence) to X-ray energies at ∼ 10 −3 L Edd . Finally, we find that the jet break luminosity scales as L ν,jet ∝ L 0.56±0.05 X (very similar to the radio-X-ray correlation), and radio-faint BHXBs have fainter jet breaks. In quiescence the jet break luminosity exceeds the X-ray luminosity.

We find a strong correlation between the optical outburst amplitude ∆V and orbital period P orb for the soft X-ray transient sources with orbital periods less than 1 day. By fitting the observed values for 8 X-ray transients we determine an empirical relation that can be used to predict the orbital period of an X-ray transient given only its outburst amplitude: ∆V = 14.36 − 7.63 log P orb (h).For periods less than 12 hrs we determine a relation for the absolute magnitude of the accretion disc during outburst, which then allows us to estimate the distances to the sources.

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A rapid timing analysis of Very Large Telescope (VLT)/ULTRACAM (optical) and RXTE (Xray) observations of the Galactic black hole binary GX 339−4 in the low/hard, post-outburst state of 2007 June is presented. The optical light curves in the r , g and u filters show slow (∼20 s) quasi-periodic variability. Upon this is superposed fast flaring activity on times approaching the best time resolution probed (∼50 ms in r and g ) and with maximum strengths of more than twice the local mean. Power spectral analysis over ∼0.004-10 Hz is presented, and shows that although the average optical variability amplitude is lower than that in X-rays, the peak variability power emerges at a higher Fourier frequency in the optical. Energetically, we measure a large optical versus X-ray flux ratio, higher than that seen on previous occasions when the source was fully jet dominated. Such a large ratio cannot be easily explained with a disc alone. Studying the optical-X-ray cross-spectrum in Fourier space shows a markedly different behaviour above and below ∼0.2 Hz. The peak of the coherence function above this threshold is associated with a short optical time lag with respect to X-rays, also seen as the dominant feature in the time-domain cross-correlation at ≈150 ms. The rms energy spectrum of these fast variations is best described by distinct physical components over the optical and X-ray regimes, and also suggests a maximal irradiated disc fraction of 20 per cent around 5000 Å. If the constant time delay is due to propagation of fluctuations to (or within) the jet, this is the clearest optical evidence to date of the location of this component. The low-frequency quasi-periodic oscillation is seen in the optical but not in X-rays, and is associated with a low coherence. Evidence of reprocessing emerges at the lowest Fourier frequencies, with optical lags at ∼10 s and strong coherence in the blue u filter. Consistent with this, simultaneous optical spectroscopy also shows the Bowen fluorescence blend, though its emission location is

Optical spectra were obtained of the optical counterpart of the high-latitude (b^62¡) soft X-ray transient XTE J1118]480 near its quiescent state (R^18.3) with the new 6.5 m Multiple Mirror Telescope and the 4.2 m William Herschel Telescope. The spectrum exhibits broad, double-peaked emission lines of hydrogen (FWHM^2400 km s~1) arising from an accretion disk superposed with absorption lines of a late-type secondary star. Cross-correlation of the 27 individual spectra with late-type stellar template spectra reveals a sinusoidal variation in radial velocity with amplitude K \ 701^10 km s~1 and orbital period P \ 0.169930^0.000004 days. The mass function, 6.1^0.3 is a Ðrm lower limit on the M _ , mass of the compact object and strongly implies that it is a black hole. We estimate the spectral type of the secondary to be K7 VÈM0 V, and that it contributes 28%^2% of the light in the 5800È6400 The photometric period measured during the outburst is 0.5% longer than our orbital M _ . period and probably reÑects superhump modulations, as observed in some other soft X-ray transients. The estimated distance is d \ 1.9^0.4 kpc, corresponding to a height of 1.7^0.4 kpc above the Galactic plane. The spectroscopic, photometric, and dynamical results indicate that XTE J1118]480 is the Ðrst Ðrmly identiÐed black hole X-ray system in the Galactic halo.

Stellar-mass black holes (BHs) are mostly found in x-ray transients, a subclass of x-ray binaries that exhibit violent outbursts. None of the 50 galactic BHs known show eclipses, which is surprising for a random distribution of inclinations. Swift J1357.2-093313 is a very faint x-ray transient detected in 2011. On the basis of spectroscopic evidence, we show that it contains a BH in a 2.8-hour orbital period. Further, high-time-resolution optical light curves display profound dips without x-ray counterparts. The observed properties are best explained by the presence of an obscuring toroidal structure moving outward in the inner disk, seen at very high inclination. This observational feature should play a key role in models of inner accretion flows and jet collimation mechanisms in stellar-mass BHs.