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Register a new userFUSE Observations of a Full Orbit of Scorpius X-1
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We obtained UV spectra of X-ray binary Scorpius X-1 in the 900-1200 A range with the Far Ultraviolet Spectroscopic Explorer over the full 0.79 day binary orbit. The strongest emission lines are the doublet of O VI at 1032,1038 A and the C III complex at 1175 A. The spectrum is affected by a multitude of narrow interstellar absorption lines, both atomic and molecular. Examination of line variability and Doppler tomograms suggests emission from both the neighborhood of the donor star and the accretion disk. Models of turbulence and Doppler broadened Keplerian disk lines Doppler shifted with the orbit of the neutron star added to narrow Gaussian emission lines with undetermined Doppler shift fit the data with consistent values of disk radius, inclination, and radial line brightness profile. The Doppler shift of the narrow component with the orbit suggests an association with the donor star. We test our line models with previously analyzed near UV spectra obtained with the Hubble Space Telescope Goddard High Resolution Spectrograph and archival spectra obtained with the HST Cosmic Origins Spectrograph.
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We observed an entire 1.7 day orbit of the X-ray binary Hercules X-1 with the Far Ultraviolet Spectroscopic Explorer (FUSE). Changes in the O VI 1032,1037 line profiles through eclipse ingress and egress indicate a Keplerian accretion disk spinning prograde with the orbit. These observations may show the first double-peaked accretion disk line profile to be seen in the Hercules X-1 system. Doppler tomograms of the emission lines show a bright spot offset from the Roche lobe of the companion star HZ Her, but no obvious signs of the accretion disk. Simulations show that the bright spot is too far offset from the Roche lobe to result from uneven X-ray heating of its surface. The absence of disk signatures in the tomogram can be reproduced in simulations which include absorption from a stellar wind. We attempt to diagnose the state of the emitting gas from the C III 977, C III 1175, and N III 991 emission lines. The latter may be enhanced through Bowen fluorescence.
The orbital period of Sco X-1 was first identified by Gottlieb et al. (1975). While this has been confirmed on multiple occasions, this work, based on nearly a century of photographic data, has remained the reference in defining the system ephemeris ever since. It was, however, called into question when Vanderlinde et al. (2003) claimed to find the one-year alias of the historical period in RXTE/ASM data and suggested that this was the true period rather than that of Gottlieb et al. (1975). We examine data from the All Sky Automated Survey (ASAS) spanning 2001-2009. We confirm that the period of Gottlieb et al. (1975) is in fact the correct one, at least in the optical, with the one-year alias strongly rejected by these data. We also provide a modern time of minimum light based on the ASAS data.
We modelled optical light curves of Sco~X-1 obtained by the Kepler space telescope during K2 mission. Modelling was performed for the case of the strong heating of the optical star and accretion disc by X-rays. In the considered model the optical star fully filled its Roche lobe. We investigated the inverse problem in wide ranges of values of model parameters and estimated following parameters of Sco X-1: the mass ratio of components $q=M_x/M_v=3.6$ ($3.5-3.8$), where $M_x$ and $M_v$ were masses of the neutron and optical stars correspondingly, the orbital inclination was $i=30^{circ}$ ($25^{circ}-34^{circ}$). In the brackets uncertainties of parameters $q$ and $i$ were shown, they originated due to uncertainties of characteristics of the physical model of Sco X-1. The temperature of non-heated optical star was $T_2 = 2500-3050$ K, its radius was $R_2=1.25R_{odot}=8.7times 10^{10}$ cm, and its bolometric luminosity was $L_{bol}=(2.1-4.6)times 10^{32}$ erg s$^{-1}$. The mass of the star was $M_vsimeq 0.4M_{odot}$. The contribution of the X-ray heated accretion disc dominated in the total optical emission of Sco~X-1. The transition between low and high states occurred due to the increase of X-ray luminosity by a factor $2-3$.
The solar disk is among the brightest gamma-ray sources in the sky. It is also among the most mysterious. No existing model fully explains the luminosity, spectrum, time variability, and morphology of its emission. We perform the first analysis of solar-disk gamma rays over a full 11-year solar cycle, utilizing a powerful new method to differentiate solar signals from astrophysical backgrounds. We produce: (i) a robustly measured spectrum from 100 MeV to 100 GeV, reaching a precision of several percent in the 1-10 GeV range, (ii) new results on the anti-correlation between solar activity and gamma-ray emission, (iii) strong constraints on short-timescale variability, ranging from hours to years, and (iv) new detections of the equatorial and polar morphologies of high-energy gamma rays. Intriguingly, we find no significant energy dependence in the time variability of solar-disk emission, indicating that strong magnetic-field effects close to the solar surface, rather than modulation throughout the heliosphere, must primarily control the flux and morphology of solar-disk emission.
We present results from the first radio observations of a complete orbit (~ 17 days) of the neutron star X-ray binary Circinus X-1 using the Australia Telescope Compact Array Broadband Backend, taken while the system was in an historically faint state. We have captured the rapid rise and decline of a periastron passage flare, with flux densities for 9 days prior to the event stable at ~ 1 mJy at 5.5 GHz and ~ 0.5 mJy at 9 GHz. The highest flux densities of 43.0 +/- 0.5 mJy at 5.5 GHz and 29.9 +/- 0.6 mJy at 9 GHz were measured during the flares decline (MJD 55206.69) which continues towards pre-flare flux densities over the following 6 days. Imaging of pre-flare data reveals steady structure including two stable components within 15 arc-seconds of the core which we believe may be persistent emission regions within the systems outflows, one of which is likely associated with the systems counter-jet. Unlike past observations carried out in the systems brighter epochs, we observe no significant structural variations within approx 3 arc-seconds of the cores position. Model subtraction and difference mapping provide evidence for variations slightly further from the core: up to 5 away. If related to the observed core flare, then these variations suggest very high outflow velocities with {Gamma} > 35, though this can be reduced significantly if we invoke phase delays of at least one orbital period. Interestingly, the strongest structural variations appear to the north west of the core, opposite to the strongest arcsec-scale emission historically. We discuss the implications of this behaviour, including the possibility of precession or a kinked approaching jet.
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