X-ray observations have revealed that many microquasars and low-mass X-ray binaries (LMXBs) exhibit narrow absorption features identified with resonant absorption from Fe XXV and Fe XXVI and other ...abundant ions. In many well studied systems there is evidence for blue-shifts, indicating outflowing plasmas. We succesfully model the changes in both the X-ray continuum and the Fe absorption features during dips from all the bright dipping LMXBs observed by XMM-Newton (EXO 0748-676, XB 1254-690, X 1624-490, MXB 1659-298, 4U 1746-371 and XB 1916-053) as resulting primarily from an increase in column density and a decrease in the ionization state of a highly-ionized absorber in a similar way as was done for XB 1323-619. This implies that the complex spectral changes in the X-ray continua observed from the dip sources as a class can be most simply explained primarily by changes in the highly ionized absorbers present in these systems. There is no need to invoke unusual abundances or partial covering of extended emission regions. Outside of the dips, the absorption line properties do not vary strongly with orbital phase. This implies that the ionized plasma has a cylindrical geometry with a maximum column density close to the plane of the accretion disk. Since dipping sources are simply normal LMXBs viewed from close to the orbital plane this implies that ionized plasmas are a common feature of LMXBs.
We report on Chandra grating spectra of the stellar-mass black hole GRS 1915+105 obtained during a novel, highly obscured state. As the source entered this state, a dense, massive accretion disk wind ...was detected through strong absorption lines. Photoionization modeling indicates that it must originate close to the central engine, orders of magnitude from the outer accretion disk. Strong, nearly sinusoidal flux variability in this phase yielded a key insight: the wind is blueshifted when its column density is relatively low, but redshifted as it approaches the Compton-thick threshold. At no point does the wind appear to achieve the local escape velocity; in this sense, it is a "failed wind." Later observations suggest that the disk ultimately fails to keep even the central engine clear of gas, leading to heavily obscured and Compton-thick states characterized by very strong Fe K emission lines. Indeed, these later spectra are successfully described using models developed for obscured active galactic nuclei (AGNs). We discuss our results in terms of the remarkable similarity of GRS 1915+105 deep in its "obscured state" to Seyfert 2 and Compton-thick AGNs, and we explore how our understanding of accretion and obscuration in massive black holes is impacted by our observations.
The dense cores of X-ray emitting gaseous haloes of large elliptical galaxies with temperatures kT≲ 0.8 keV show two prominent Fe xvii emission features, which provide a sensitive diagnostic tool to ...measure the effects of resonant scattering. We present here high-resolution spectra of five bright nearby elliptical galaxies, obtained with the reflection grating spectrometers (RGS) on the XMM-Newton satellite. The spectra for the cores of four of the galaxies show the Fe xvii line at 15.01 Å being suppressed by resonant scattering. The data for NGC 4636 in particular allow the effects of resonant scattering to be studied in detail and to prove that the 15.01 Å line is suppressed only in the dense core and not in the surrounding regions. Using deprojected density and temperature profiles for this galaxy obtained with the Chandra satellite, we model the radial intensity profiles of the strongest resonance lines, accounting for the effects of resonant scattering, for different values of the characteristic turbulent velocity. Comparing the model to the data, we find that the isotropic turbulent velocities on spatial scales smaller than ≈1 kpc are less than 100 km s−1 and the turbulent pressure support in the galaxy core is smaller than 5 per cent of the thermal pressure at the 90 per cent confidence level, and less than 20 per cent at 95 per cent confidence. Neglecting the effects of resonant scattering in spectral fitting of the inner 2 kpc core of NGC 4636 will lead to underestimates of the chemical abundances of Fe and O by ∼10–20 per cent.
Abstract In this study, we investigate interstellar absorption lines along the line of sight toward the galactic low-mass X-ray binary Cygnus X-2. We combine absorption line data obtained from ...high-resolution X-ray spectra collected with the Chandra and XMM-Newton satellites, along with far-UV absorption lines observed by the Hubble Space Telescope’s (HST) Cosmic Origins Spectrograph (COS) instrument. Our primary objective is to understand the abundance and depletion of oxygen, iron, sulfur, and carbon. To achieve this, we have developed an analysis pipeline that simultaneously fits both the UV and X-ray data sets. This novel approach takes into account the line-spread function of HST/COS, enhancing the precision of our results. We examine the absorption lines of Fe ii , S ii , C ii , and C i present in the far-UV spectrum of Cygnus X-2, revealing the presence of at least two distinct absorbers characterized by different velocities. Additionally, we employ Cloudy simulations to compare our findings concerning the ionic ratios for the studied elements. We find that gaseous iron and sulfur exist in their singly ionized forms, Fe ii and S ii , respectively, while the abundances of C ii and C i do not agree with the Cloudy simulations of the neutral ISM. Finally, we explore discrepancies in the X-ray atomic data of iron and discuss their impact on the overall abundance and depletion of iron.
Our Swift monitoring program triggered two joint XMM-Newton, NuSTAR, and HST observations on 11 and 21 December 2016 targeting NGC 3783 because its soft X-ray continuum was heavily obscured. ...Consequently, emission features, including the O VII radiative recombination continuum, stand out above the diminished continuum. We focus on the photoionized emission features in the December 2016 Reflection Grating Spectrometer (RGS) spectra, and compare them to the time-averaged RGS spectrum obtained in 2000–2001 when the continuum was unobscured. A two-phase photoionized plasma is required to account for the narrow emission features. These narrow emission features are weakly varying between 2000–2001 and December 2016. We also find a statistically significant broad emission component in the time-averaged RGS spectrum in 2000–2001. This broad emission component is significantly weaker in December 2016, suggesting that the obscurer is farther away than the X-ray broad-line region. In addition, by analyzing the archival high-resolution X-ray spectra, we find that nine photoionized absorption components with different ionization parameters and kinematics are required for the warm absorber in X-rays.
Current measurements show that the observed fraction of Compton-thick (CT) active galactic nuclei (AGN) is smaller than the expected values needed to explain the cosmic X-ray background. Prior fits ...to the X-ray spectrum of the nearby Seyfert-2 galaxy NGC 5347 (z = 0.00792, D = 35.5 Mpc ) have alternately suggested a CT and Compton-thin source. Combining archival data from Suzaku, Chandra, and-most importantly-new data from NuSTAR, and using three distinct families of models, we show that NGC 5347 is an obscured CTAGN (NH > 2.23 × 1024 cm−2). Its 2-30 keV spectrum is dominated by reprocessed emission from distant material, characterized by a strong Fe K line and a Compton hump. We found a large equivalent width of the Fe K line (EW = 2.3 0.3 keV) and a high intrinsic-to-observed flux ratio (∼100). All of these observations are typical for bona fide CTAGN. We estimate a bolometric luminosity of Lbol 0.014 0.005 LEdd.. The Chandra image of NGC 5347 reveals the presence of extended emission dominating the soft X-ray spectrum (E < 2 keV), which coincides with the O iii emission detected in Hubble Space Telescope images. Comparison to other CTAGN suggests that NGC 5347 is broadly consistent with the average properties of this source class. We simulated XRISM and Athena/X-IFU spectra of the source, showing the potential of these future missions in identifying CTAGN in the soft X-rays.
Anatomy of the AGN in NGC 5548 Mehdipour, M; Kaastra, J S; Kriss, G A ...
Astronomy and astrophysics (Berlin),
3/2015, Volume:
575
Journal Article
Peer reviewed
An extensive multi-satellite campaign on NGC 5548 has revealed this archetypal Seyfert-1 galaxy to be in an exceptional state of persistent heavy absorption. Our observations taken in 2013-2014 with ...XMM-Newton, Swift, NuSTAR, INTEGRAL, Chandra, HST and two ground-based observatories have together enabled us to establish that this unexpected phenomenon is caused by an outflowing stream of weakly ionised gas (called the obscurer), extending from the vicinity of the accretion disk to the broad-line region. In this work we present the details of our campaign and the data obtained by all the observatories. We determine the spectral energy distribution of NGC 5548 from near-infrared to hard X-rays by establishing the contribution of various emission and absorption processes taking place along our line of sight towards the central engine. We thus uncover the intrinsic emission and produce a broadband continuum model for both obscured (average summer 2013 data) and unobscured (<2011) epochs of NGC 5548. Our results suggest that the intrinsic NIR/optical/UV continuum is a single Comptonised component with its higher energy tail creating the "softX-ray excess". This component is compatible with emission from a warm, optically-thick corona as part of the inner accretion disk. We then investigate the effects of the continuum on the ionisation balance and thermal stability of photoionised gas for unobscured and obscured epochs.
The mechanisms that drive disk winds are a window into the physical processes that underlie the disk. Stellar-mass black holes are an ideal setting in which to explore these mechanisms, in part ...because their outbursts span a broad range in mass accretion rate. We performed a spectral analysis of the disk wind found in six Chandra/HETG observations of the black hole candidate 4U 1630−472, covering a range of luminosities over two distinct spectral states. We modeled both wind absorption and extended wind re-emission components using PION, a self-consistent photoionized absorption model. In all but one case, two photoionization zones were required in order to obtain acceptable fits. Two independent constraints on launching radii, obtained via the ionization parameter formalism and the dynamical broadening of the re-emission, helped characterize the geometry of the wind. The innermost wind components ( ) tend toward small volume filling factors, high ionization, densities up to , and outflow velocities of ∼0.003c. These small launching radii and large densities require magnetic driving, as they are inconsistent with numerical and analytical treatments of thermally driven winds. Outer wind components ( ) are significantly less ionized and have filling factors near unity. Their larger launching radii, lower densities ( ), and outflow velocities (∼0.0007c) are nominally consistent with thermally driven winds. The overall wind structure suggests that these components may also be part of a broader MHD outflow and perhaps better described as magneto-thermal hybrid winds.
In 2014 the NGC 5548 Space Telescope and Optical Reverberation Mapping campaign discovered a two-month anomaly when variations in the absorption and emission lines decorrelated from continuum ...variations. During this time the soft X-ray part of the intrinsic spectrum had been strongly absorbed by a line-of-sight (LOS) obscurer, which was interpreted as the upper part of a disk wind. Our first paper showed that changes in the LOS obscurer produces the decorrelation between the absorption lines and the continuum. A second study showed that the base of the wind shields the broad emission-line region (BLR), leading to the emission-line decorrelation. In that study, we proposed the wind is normally transparent with no effect on the spectrum. Changes in the wind properties alter its shielding and affect the spectral energy distribution (SED) striking the BLR, producing the observed decorrelations. In this work we investigate the impact of a translucent wind on the emission lines. We simulate the obscuration using XMM-Newton, NuSTAR, and Hubble Space Telescope observations to determine the physical characteristics of the wind. We find that a translucent wind can contribute a part of the He ii and Fe K emission. It has a modest optical depth to electron scattering, which explains the fainter far-side emission in the observed velocity-delay maps. The wind produces the very broad base seen in the UV emission lines and may also be present in the Fe K line. Our results highlight the importance of accounting for the effects of such winds in the analysis of the physics of the central engine.
Context.
NGC 985 was observed by
XMM-Newton
twice in 2015, revealing that the source was coming out from a soft X-ray obscuration event that took place in 2013. These kinds of events are possibly ...recurrent since a previous
XMM-Newton
archival observation in 2003 also showed signatures of partial obscuration.
Aims.
We have analyzed the high-resolution X-ray spectra of NGC 985 obtained by the Reflection Grating Spectrometer onboard
XMM-Newton
in 2003, 2013, and 2015 in order to characterize the ionized absorbers superimposed to the continuum and to study their response as the ionizing flux varies.
Methods.
The spectra were analyzed with the SPEX fitting package and the photoionization code CLOUDY.
Results.
We found that up to four warm absorber (WA) components were present in the grating spectra of NGC 985, plus a mildy ionized (log
ξ
∼ 0.2−0.5) obscuring (
N
H
∼ 2 × 10
22
cm
−2
) wind outflowing at ∼ − 6000 km s
−1
. The absorbers have a column density that ranges from ∼10
21
to a few times 10
22
cm
−2
, and ionization parameters ranging from log
ξ
∼ 1.6 to ∼2.9. The most ionized component is also the fastest, moving away at ∼ − 5100 km s
−1
, while the others outflow in two kinematic regimes, ∼ − 600 and ∼ − 350 km s
−1
. These components showed variability at different time scales in response to changes in the ionizing continuum. Assuming that these changes are due to photoionization and recombination mechanisms, we have obtained upper and lower limits on the density of the gas. We used these limits to pinpoint the location of the warm absorbers, finding that the closest two components are at parsec-scale distances, while the rest may extend up to tens of parsecs from the central source. With these constraints on the density and location, we found that the fastest, most ionized WA component accounts for the bulk of the kinetic luminosity injected back into the interstellar medium of the host galaxy, which is on the order of 0.8% of the bolometric luminosity of NGC 985. According to the models, this amount of kinetic energy per unit time would be sufficient to account for cosmic feedback.
Conclusions.
Observations of the onset and conclusion of transient obscuring events in active galactic nuclei are a key tool to understand both the dynamics and physics of the gas in their innermost regions, and also to study the response of the surrounding gas as the ionizing continuum varies.
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