X-ray Binary X2127 Research Articles

Theoretical investigation of the neutron star in low-mass X-ray binary X1822-371 (V691 CrA)

We propose a model for the neutron star in low-mass X-ray binary (LMXB) X1822-371 (V691 CrA) (Munoz-Darius et al. in Astrophys. J. 635:502, 2005). Here we investigate the physical phenomena of the neutron star in LMXB X1822-371 (V691 CrA) by using the Tolman-IV solution (Tolman in Phys. Rev. 55:364, 1939). Using our model, we evaluate central density (\(\rho_{0}\)), surface density (\(\rho_{b}\)), central pressure (\(p _{0}\)), surface redshift (\(Z _{s}\)) and probable radius of the above mentioned neutron star, which is very much consistent with reported data. We also obtain a possible equation of state (EoS) of the star which is physically acceptable.

X-ray spectroscopy of the ADC source X1822-371 withChandraandXMM-Newton

The eclipsing low-mass X-ray binary X1822-371 is the prototype of the accretion disc corona (ADC) sources. We analyse two Chandra observations and one XMM-Newton observation to study the discrete features and their variation as a function of the orbital phase, deriving constraints on the temperature, density, and location of the plasma responsible for emission lines. The HETGS and XMM/Epic-pn observed X1822-371 for 140 and 50 ks, respectively. We extracted an averaged spectrum and five spectra from five selected orbital-phase intervals that are 0.04-0.25, 0.25-0.50, 0.50-0.75, 0.75-0.95, and, finally, 0.95-1.04; the orbital phase zero corresponds to the eclipse time. All spectra cover the energy band between 0.35 and 12 keV. We confirm the presence of local neutral matter that partially covers the X-ray emitting region; the equivalent hydrogen column is $5 \times 10^{22}$ cm$ ^{-2}$ and the covered fraction is about 60-65%. We identify emission lines from highly ionised elements, and a prominent fluorescence iron line associated with a blending of FeI-FeXV resonant transitions. The transitions of He-like ions show that the intercombination dominates over the forbidden and resonance lines. The line fluxes are the highest during the orbital phases between 0.04 and 0.75. We discuss the presence of an extended, optically thin corona with optical depth of about 0.01 that scatters the X-ray photons from the innermost region into the line of sight. The photoionised plasma producing most of the observed lines is placed in the bulge at the outer radius of the disc distant from the central source of $6 \times 10^{10}$ cm. The OVII and the fluorescence iron line are probably produced in the photoionised surface of the disc at inner radii. (Abridged)

Mapping of the Disc Structure of the Neutron Star X-ray Binary X1822-371

We report the results of simultaneous optical/Xray observations of X1822-371 at 0.1 second time resolution. The preliminary analysis finds no correlation between the optical/X-ray light curves. We aim to constrain the vertical structure and radius of the accretion disc.

The “K‐Correction” for Irradiated Emission Lines in LMXBs: Evidence for a Massive Neutron Star in X1822−371 (V691 CrA)

We study the K-correction for the case of emission lines formed in the X-ray-illuminated atmosphere of a Roche lobe-filling star. We compute the K-correction as a function of the mass ratio q and the disk flaring angle α using a compact binary code in which the companion's Roche lobe is divided into 105 resolution elements. We also study the effect of the inclination angle in the results. We apply our model to the case of the neutron star low-mass X-ray binary X1822-371 (V691 CrA), where a K-emission velocity Kem = 300 ± 8 km s-1 has been measured by Casares et al. Our numerical results, combined with a previous determination of system parameters, yields 1.61 M☉ ≤ MNS ≤ 2.32 M☉ and 0.44 M☉ ≤ M2 ≤ 0.56 M☉ for the two binary components (i.e., 0.24 ≤ q ≤ 0.27), which provide compelling evidence for a massive neutron star in this system. We also discuss the implications of these masses into the evolutionary history of the binary.

A new mass-ratio for the X-ray binary X2127+119 in M 15?

The luminous low-mass X-ray binary X2127+119 in the core of the globular cluster M 15 (NGC 7078), which has an orbital period of 17 hours, has long been assumed to contain a donor star evolving off the main sequence, with a mass of 0.8 M ○. (the main-sequence turn-off mass for M 15). We present orbital-phase-resolved spectroscopy of X2127+119 in the Ha and Me I λ6678 spectral region, obtained with the Hubble Space Telescope. We show that these data are incompatible with the assumed masses of X2127+119's component stars. The continuum eclipse is too shallow, indicating that much of the accretion disc remains visible during eclipse, and therefore that the size of the donor star relative to the disc is much smaller in this high-inclination system than the assumed mass-ratio allows. Furthermore, the flux on X2127+119's He I λ6678 emission, which has a velocity that implies an association with the stream-disc impact region, remains unchanged through eclipse, implying that material from the impact region is always visible. This should not be possible if the previously-assumed mass ratio is correct. In addition, we do not detect any spectral features from the donor star, which is unexpected for a 0.8-M ○. sub-giant in a system with a 17-h period.

The X-ray binary X2127+119 in M15: evidence for a very low mass, stripped-giant companion

We present integral field spectroscopy of X2127+119, the luminous X-ray binary in the globular cluster M15, obtained with INTEGRAL/WYFFOS on the William Herschel Telescope. We find that tomograms of He II λ4686 line profiles appear to be incompatible with the previously assumed view of X2127+119, in which the binary consists of a 1.4-M ○. neutron star and a 0.8-M ○. subgiant companion near the main-sequence turn-off for M15. Our data imply a much smaller mass ratio M 2 /M X of ∼0.1. We find that models of X2127+119 with black hole compact objects give a poor fit to our data, while a neutron-star compact object is consistent with the data, implying that the companion of X2127+119 may have a much lower mass (∼0.1 M ○. ) than previously assumed. As a ∼0.1-M ○. main-sequence star would be unable to fill its Roche lobe in a binary with the orbital period of X2127+119 (17.1 h), the companion is likely to be the remnant of a significantly more massive star which has had most of its envelope stripped away.

Mass outflow from the X-ray binary X2127 + 119 in M15

The bright X-ray binary X2127 + 119 in the core of the globular cluster M15 has long been thought to be in an unusual evolutionary state, in which the binary is embedded in a common envelope. Support for this idea comes from the absorption lines of X2127 + 119, which are blueshifted at all orbital phases, indicating the existence of outflows from the system. A common-envelope scenario implies that the absorption lines should exhibit maximum blueshift near mid-eclipse (binary phase 0.0). We have re-analysed Isaac Newton Telescope spectra of X2127 + 119 obtained in 1986, 1987 and 1988 using the latest orbital ephemeris (substantially different from that used in the original analysis), and find that the orbital phase at which the absorption lines show a maximum blueshift is not 0.0, but rather 0.25-0.3. These results indicate that a common-envelope scenario for X2127 + 119 may not work. In addition, from spectrograms of the He II λ4686 line, we report the first tentative detection of the companion star of X2127 + 119.

X‐Ray Observations of X2127+119/AC 211 in the Metal‐poor Globular Cluster M15: An X‐Ray Measure of Metallicity?

We present results from observations of the 17.1 hr low-mass X-ray binary X2127+119 (AC 211) in M15 obtained with the broadband X-ray telescope (BBXRT) in 1990 December and observations obtained with the solid state spectrometer (SSS) together with the monitor proportional counter (MPC) on the Einstein Observatory in 1978 and 1979. The continuum can be well described with the two-component model of a blackbody (kT ~ 1 keV) and a power law that was found to fit the EXOSAT medium-energy data. Short-term variability observed by the SSS and MPC was related to changes in the intensities of both components in this description. The SSS and MPC observed factor of 10 differences in column density in observations separated by a few binary orbits. These observations confirm correlations between the steepness of the spectrum and the column density, and column density with phase. The percentage contribution of the blackbody is anticorrelated with the factor of 4 variations in the apparent luminosity, but other correlations are weak. A 1000 s observation by BBXRT at photometric phase 0.9 provides an upper limit of ~150 eV to narrow Fe K line emission. BBXRT spectra are generally inconsistent with the overall cluster metallicity of 1% of solar, although complex spectral models can be more consistent with the cluster metallicity. A model separating the absorption of H and He from the metals gives 1.25+ 0.03−0.2×1018 cm-2 for the column density of metals in the absorbing gas associated with the binary system. The noted correlations between spectral parameters, luminosity, and their relation to orbital phase are consistent with a disk plus moderate-sized corona interpretation.

HST UV observations of the accretion disk corona X-ray binary X1822-371

The Faint Object Spectrograph on the Hubble Space Telescope has provided the first ultraviolet orbital light curve of the low-mass X-ray binary X1822-371. The shape of the UV light curve changes with wavelength providing the first direct clues to the temperature of the various system components. The data support the idea that the system contains a thick, structured accretion disk.