693 research outputs found
The Symbiotic System SS73 17 Seen with Suzaku
We observed with Suzaku the symbiotic star SS73 17, motivated by the
discovery by the INTEGRAL satellite and the Swift BAT survey that it emits hard
X-rays. Our observations showed a highly-absorbed X-ray spectrum with NH >
10^23 cm-2, equivalent to A_V > 26, although the source has B magnitude 11.3
and is also bright in UV. The source also shows strong, narrow iron lines
including fluorescent Fe K as well as Fe xxv and Fe xxvi. The X-ray spectrum
can be fit with a thermal model including an absorption component that
partially covers the source. Most of the equivalent width of the iron
fluorescent line in this model can be explained as a combination of
reprocessing in a dense absorber plus reflection off a white dwarf surface, but
it is likely that the continuum is partially seen in reflection as well. Unlike
other symbiotic systems that show hard X-ray emission (CH Cyg, RT Cru, T CrB,
GX1+4), SS73 17 is not known to have shown nova-like optical variability, X-ray
flashes, or pulsations, and has always shown faint soft X-ray emission. As a
result, although it is likely a white dwarf, the nature of the compact object
in SS73 17 is still uncertain. SS73 17 is probably an extreme example of the
recently discovered and relatively small class of hard X-ray emitting symbiotic
systems.Comment: 6 pages, accepted by PASJ for 2nd Suzaku Special Issu
Modeling of Photoionized Plasmas
In this paper I review the motivation and current status of modeling of
plasmas exposed to strong radiation fields, as it applies to the study of
cosmic X-ray sources. This includes some of the astrophysical issues which can
be addressed, the ingredients for the models, the current computational tools,
the limitations imposed by currently available atomic data, and the validity of
some of the standard assumptions. I will also discuss ideas for the future:
challenges associated with future missions, opportunities presented by improved
computers, and goals for atomic data collection.Comment: 17 pages, 8 figures, to appear in the proceedings of Xray2010,
Utrecht, the Netherlands, March 15-17 201
An X-Ray Spectroscopic Study of the SMC X-1/Sk 160 System
We have investigated the composition and distribution of the wind of Sk 160,
the supergiant companion of the X-ray star SMC X-1, by comparing an X-ray
spectrum of the source, obtained with the ASCA observatory, during an eclipse
with the computed spectra of reprocessed radiation from circumstellar matter
with various density distributions. We show that the metal abundance in the
wind of Sk 160 is no greater than a few tenths of solar, as has been determined
for other objects in the Magellanic Clouds. We also show that the observed
X-ray spectrum is not consistent with the density distributions of
circumstellar matter of the spherically symmetric form derived for line-driven
winds, nor with the density distribution derived from a hydrodynamic simulation
of the X-ray perturbed and line-driven wind by Blondin & Woo (1995).Comment: 35 pages including 16 figures, uses AASTeX v5.0.2, accepted to Ap
Wind suppression by X-rays in Cygnus X-3
Context. The radiatively driven wind of the primary star in wind-fed X-ray binaries can be suppressed by the X-ray irradiation of the compact secondary star. This causes feedback between the wind and the X-ray luminosity of the compact star.Aims. We aim to estimate how the wind velocity on the face-on side of the donor star depends on the spectral state of the high-mass X-ray binary Cygnus X-3.Methods. We modeled the supersonic part of the wind by computing the line force (force multiplier) with the Castor, Abbott & Klein formalism and XSTAR physics and by solving the mass conservation and momentum balance equations. We computed the line force locally in the wind considering the radiation fields from both the donor and the compact star in each spectral state. We solved the wind equations at different orbital angles from the line joining the stars and took the effect of wind clumping into account. Wind-induced accretion luminosities were estimated using the Bondi-Hoyle-Lyttleton formalism and computed wind velocities at the compact star. We compared them to those obtained from observations.Results. We found that the ionization potentials of the ions contributing the most to the line force fall in the extreme-UV region (100-230 angstrom). If the flux in this region is high, the line force is weak, and consequently, the wind velocity is low. We found a correlation between the luminosities estimated from the observations for each spectral state of Cyg X-3 and the computed accretion luminosities assuming moderate wind clumping and a low mass of the compact star. For high wind clumping, this correlation disappears. We compared the XSTAR method used here with the comoving frame method and found that they agree reasonably well with each other.Conclusions. We show that soft X-rays in the extreme-UV region from the compact star penetrate the wind from the donor star and diminish the line force and consequently the wind velocity on the face-on side. This increases the computed accretion luminosities qualitatively in a similar manner as observed in the spectral evolution of Cyg X-3 for a moderate clumping volume filling factor and a compact star mass of a few (2-3) solar masses.Peer reviewe
A high velocity ionised outflow and XUV photosphere in the narrow emission line quasar PG1211+143
We report on the analysis of a ~60 ksec XMM observation of the bright, narrow
emission line quasar PG 1211+143. Absorption lines are seen in both EPIC and
RGS spectra corresponding to H- and He-like ions of Fe, S, Mg, Ne, O, N and C.
The observed line energies indicate an ionised outflow velocity of ~24000 km
s^-1. The highest energy lines require a column density of N_H ~ 5 x 10^23
cm^-2, at an ionisation parameter of log(xi) ~ 3.4. If the origin of this high
velocity outflow lies in matter being driven from the inner disc, then the flow
is likely to be optically thick within a radius ~130 Schwarzschild radii,
providing a natural explanation for the Big Blue Bump (and strong soft X-ray)
emission in PG 1211+143.Comment: Accepted by MNRAS; Table 1 correcte
Radiative and Auger decay data for modelling nickel K lines
Radiative and Auger decay data have been calculated for modelling the K lines
in ions of the nickel isonuclear sequence, from Ni up to Ni. Level
energies, transition wavelengths, radiative transition probabilities, and
radiative and Auger widths have been determined using Cowan's Hartree--Fock
with Relativistic corrections (HFR) method. Auger widths for the third-row ions
(Ni--Ni) have been computed using single-configuration average
(SCA) compact formulae. Results are compared with data sets computed with the
AUTOSTRUCTURE and MCDF atomic structure codes and with available experimental
and theoretical values, mainly in highly ionized ions and in the solid state.Comment: submitted to ApJS. 42 pages. 12 figure
The First Detection of [O IV] from an Ultraluminous X-ray Source with Spitzer: Evidence of High Unbeamed Luminosity in Holmberg II ULX
We present the first Spitzer Infrared Spectrograph (IRS) observations of the [O IV] 25.89 micron emission line detected from the ultraluminous X-ray source (ULX) in Holmberg II. This line is a well established signature of high excitation, usually associated with AGN. Its detection suggests that the ULX has a strong impact on the surrounding gas. A Spitzer high resolution spectral map shows that the [O IV] is coincident with the X-ray position of the Holmberg II ULX. We find that the luminosity and the morphology of the line emission is consistent with photoionization by the soft X-ray and far ultraviolet (FUV) radiation from the accretion disk of the binary system and inconsistent with narrow beaming. We show that the emission nebula is radiation bounded both in the line of sight direction and to the west, and probably matter bounded to the east. Evidence for a massive black hole (BH) in this ULX is mounting. Detailed photoionization models favor an intermediate mass black hole of at least 85 Solar Mass as the ionization source for the [OIV] emission. We find that the spectral type of the companion star strongly affects the expected strength of the [O IV] emission. This finding could explain the origin of [O IV] in some starburst galaxies containing black hole binaries
The First Detection of [O IV] from an Ultraluminous X-ray Source with Spitzer. I. Observational Results for Holmberg II ULX
We presen the first Spitzer Infrared Spectrograph (IRS) observations of the [O IV] 25.89 um emission line detected from the ultraluminous X-ray source (ULX) in Holmberg II. This line is a well established signature of high excitation usually associated with AGN. Its detection suggests that the ULX has a strong impact on the surrounding gas. A Spitzer high resolution spectral map shows that the [O IV] is coincident with the X-ray position of the ULX. The ratios of the [O IV] to lower ionization lines are similar to those observed in AGN, suggesting that a strong UV and X-ray source is responsible for the, photoionization. The best XMM-Newton data is used to model the X-ray band which is then extrapolated into the UV. We perform infrared and ultraviolet photometry, and use its previously published optical and radio data to construct the full SED for the ULX and its companion. The preferred model to describe the SED includes an accretion disk which dominates the soft X-rays but contributes little at UV and optical wavelengths. The optical counterpart is consistent with a B supergiant as previously suggested in other studies. The bolometric luminosity of the ULX suggests the presence of an intermediate-mass black hole with mass >85 M for sub-Eddington accretion or, alternatively, a stellar-mass black hole that is accreting at super-Eddington rates. In a follow-up second paper we perform detailed photoionization modeling of the infrared lines in order to constrain the bolometric luminosity of the ULX
- …