Suzaku X-ray Spectra and Pulse Profile Variations during the Superorbital Cycle of LMC X-4

We present results from spectral and temporal analyses of Suzaku and RXTE observations of the high mass X-ray binary LMC X-4. Using the full 13 years of available RXTE/ASM data, we apply the ANOVA and Lomb normalized Periodogram methods to obtain an improved superorbital period measurement of 30.32 +/- 0.04 days. The phase-averaged X-ray spectra from Suzaku observations during the high state of the superorbital period can be modeled in the 0.6--50 keV band as the combination of a power-law with Gamma ~ 0.6 and a high-energy cutoff at ~ 25 keV, a blackbody with kT_BB ~ 0.18 keV, and emission lines from Fe K_alpha, O VIII, and Ne IX (X Lyalpha). Assuming a distance of 50 kpc, The source has luminosity L_X ~ 3 x 10^38 ergs s^-1 in the 2--50 keV band, and the luminosity of the soft (blackbody) component is L_BB ~ 1.5 x 10^37 ergs s^-1. The energy resolved pulse profiles show single-peaked soft (0.5-1 keV) and hard (6-10 keV) pulses but a more complex pattern of medium (2-10 keV) pulses; cross-correlation of the hard with the soft pulses shows a phase shift that varies between observations. We interpret these results in terms of a picture in which a precessing disk reprocesses the hard X-rays and produces the observed soft spectral component, as has been suggested for the similar sources Her X-1 and SMC X-1.Comment: 13 emulateapj pages, 11 figures, 4 tables; accepted for publication in Ap

FUSE Observations of a Full Orbit of Hercules X-1: Signatures of Disk, Star, and Wind

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.Comment: Accepted for publication in The Astrophysical Journa

Stellar Coronal Spectroscopy with the Chandra HETGS

Spectroscopy with the Chandra High Energy Transmission Grating Spectrometer provides details on X-ray emission and activity from young and cool stars through resolution of emission lines from a variety of ions. We are beginning to see trends in activity regarding abundances, emission measures, and variability. Here we contrast spectra of TV Crt, a weak-lined T Tauri star, with TW Hya, a Classical T Tauri star. TV Crt has a spectrum more like magnetic activity driven coronae, relative to the TW Hya spectrum, which we have interpreted as due to accretion-produced X-rays. We have also observed the long period system, IM Pegasi to search for rotational modulation, and to compare activity in a long period active binary to shorter period systems and to the pre-main sequence stars. We detected no rotational modulation, but did see long-duration flares.Comment: 5 pages, 2 figures; to be published in IAU Symposium 219: "Stars as Suns: Activity, Evolution, Planets" (Ed. A. Dupree and A. O. Benz

Hercules X-1: Empirical Models of UV Emission Lines

The UV emission lines of Hercules X-1, resolved with the HST GHRS and STIS, can be divided into broad (FWHM 750 km/s) and narrow (FWHM 150 km/s) components. The broad lines can be unambiguously identified with emission from an accretion disk which rotates prograde with the orbit. The narrow lines, previously identified with the X-ray illuminated atmosphere of the companion star, are blueshifted at both phi=0.2 and phi=0.8 and the line flux at phi=0.2 is 0.2 of the flux at phi=0.8. Line ratio diagnostics show that the density of the narrow line region is log n=13.4+/-0.2 and the temperature is T=1.0+/-0.2x10^5 K. The symmetry of the eclipse ingress suggests that the line emission on the surface of the disk is left-right symmetric relative to the orbit. Model fits to the O V, Si IV, and He II line profiles agree with this result, but fits to the N V lines suggest that the receding side of the disk is brighter. We note that there are narrow absorption components in the N V lines with blueshifts of 500 km/s.Comment: To be published in the Astrophysical Journa

Hopkins Ultraviolet Telescope Observations of Her X-1

We have obtained a far-ultraviolet spectrum of the X-ray binary Hercules X-1/HZ Herculis using the Hopkins Ultraviolet Telescope aboard the Astro-1 space shuttle mission in 1990 December. This is the first spectrum of Her X-1 that extends down to the Lyman limit at 912 A. We observed emission lines of O VI, N V, and C IV, and the far UV continuum extending to the Lyman limit. We examine the conditions of the emitting gas through line strengths, line ratios, and doublet ratios. The UV flux is lower by about a factor of 2 than expected at the orbital phase of the observation. We model the UV continuum with a simple power-law and with a detailed model of an X-ray-illuminated accretion disk and companion star. The power-law provides a superior fit, as the detailed model predicts too little flux below 1200 A. We note, however, that there are uncertainties in the interstellar reddening, in the background airglow spectrum, and in the long-term phase of the accretion disk. We have searched the data for UV line and continuum pulsations near the neutron star spin period but found none at a detectable level.Comment: 19 pages, 5 figures, accepted by the Astrophysical Journa

Models of X-ray Photoionization in LMC X-4: Slices of a Stellar Wind

We show that the orbital variation in the UV P Cygni lines of the X-ray binary LMC X-4 results when X-rays photoionize nearly the entire region outside of the X-ray shadow of the normal star. We fit models to HST GHRS observations of N V and C IV P Cygni line profiles. Analytic methods assuming a spherically symmetric wind show that the wind velocity law is well-fit by v~(1-1/r)^beta, where beta is likely 1.4-1.6 and definitely <2.5. Escape probability models can fit the observed P Cygni profiles, and provide measurements of the stellar wind parameters. The fits determine Lx/Mdot=2.6+/-0.1 x10^43 erg/s/Msun yr, where Lx is the X-ray luminosity and Mdot is the mass-loss rate of the star. Allowing an inhomogeneous wind improves the fits. IUE spectra show greater P Cygni absorption during the second half of the orbit than during the first. We discuss possible causes of this effect.Comment: 56 pages, 12 figures, to be published in the Astrophysical Journa

Chandra Grating Spectroscopy of the X-ray Binary 4U 1700-37 in a Flaring State

Chandra X-ray Observatory grating spectra of the supergiant X-ray Binary 4U 1700-37 reveal emission lines from hydrogen and helium-like S, Si, Mg, and Ne in the 4-13 A range. The spectrum also shows fluorescent lines from S, Si, and a prominent Fe K alpha line at 1.94 A. The lines contribute to the previously unaccounted "soft excess" in the flux in this range at orbital phi~0.7. The X-ray source was observed during intermittent flaring, and the strengths of the lines vary with the source state. The widths of the lines (FWHM approximately 1000-2000 km/s) can result from either Compton scattering or Doppler shifts. Power spectra of the hard X-rays show red noise and the soft X-rays and lines show in addition quasiperiodic oscillations (QPOs) and a power-spectral break. Helium-like triplets of Si and Mg suggest that the gas is not in a pure photoionization equilibrium. We discuss whether resonant scattering could affect the line ratios or whether a portion of the wind may be heated to temperatures T~10^6 K.Comment: 43 pages, 12 figures (4 in color), submitted to The Astrophysical Journa

BRIGHT [C ii] AND DUST EMISSION IN THREE z > 6.6 QUASAR HOST GALAXIES OBSERVED BY ALMA

journal_title: The Astrophysical Journal article_type: paper copyright_information: © 2016. The American Astronomical Society. All rights reserved. date_received: 2015-06-16 date_accepted: 2015-11-23 date_epub: 2015-12-29journal_title: The Astrophysical Journal article_type: paper copyright_information: © 2016. The American Astronomical Society. All rights reserved. date_received: 2015-06-16 date_accepted: 2015-11-23 date_epub: 2015-12-29journal_title: The Astrophysical Journal article_type: paper copyright_information: © 2016. The American Astronomical Society. All rights reserved. date_received: 2015-06-16 date_accepted: 2015-11-23 date_epub: 2015-12-2