In this paper we present a comprehensive study of the mass of the intermediate mass black hole candidate HLX-1 in the galaxy ESO 243-49. We analyse the continuum X-ray spectra collected by Swift, ...XMM-Newton, and Chandra with the slim disc model, slimbh, and estimate the black hole mass for the full range of inclination (inc = 0°−85°) and spin (a∗ = 0−0.998). The relativistic slimbh model is particularly suited to study high luminosity disc spectra as it incorporates the effects of advection, such as the shift of the inner disc edge towards smaller radii and the increasing height of the disc photosphere (including relativistic ray-tracing from its proper location rather than the mid-plane of the disc). We find for increasing values of inclination that a zero spin black hole has a mass range of 6300−50 900 M⊙ and a maximally spinning black hole has a mass between 16 900−191 700 M⊙. This is consistent with previous estimates and reinforces the idea that HLX-1 contains an intermediate mass black hole.
ABSTRACT
NGC 7582 (z = 0.005264; D = 22.5 Mpc) is a highly variable, changing-look AGN. In this work, we explore the X-ray properties of this source using XMM–Newton and NuSTAR archival observations ...in the 3 – 40 keV range, from 2001 to 2016. NGC 7582 exhibits a long-term variability between observations but also a short-term variability in two observations that has not been studied before. To study the variability, we perform a time-resolved spectral analysis using a phenomenological model and a physically motivated model (uxclumpy). The spectral fitting is achieved using a nested sampling Monte Carlo method. uxclumpy enables testing various geometries of the absorber that may fit AGN spectra. We find that the best model is composed of a fully covering clumpy absorber. From this geometry, we estimate the velocity, size, and distance of the clumps. The column density of the absorber in the line of sight varies from Compton-thin to Compton-thick between observations. Variability over the time-scale of a few tens of kiloseconds is also observed within two observations. The obscuring clouds are consistent with being located at a distance not larger than 0.6 pc, moving with a transverse velocity exceeding ∼700 km s−1. We could put only a lower limit on the size of the obscuring cloud being larger than 1013 cm. Given the sparsity of the observations, and the limited exposure time per observation available, we cannot determine the exact structure of the obscuring clouds. The results are broadly consistent with comet-like obscuring clouds or spherical clouds with a non-uniform density profile.
At low redshifts, the observed baryonic density falls far short of the total number of baryons predicted. Cosmological simulations suggest that these baryons reside in filamentary gas structures, ...known as the warm-hot intergalactic medium (WHIM). As a result of the high temperatures of these filaments, the matter is highly ionised such that it absorbs and emits far-UV and soft X-ray photons.
Athena
, the proposed European Space Agency X-ray observatory, aims to detect the “missing” baryons in the WHIM up to redshifts of
z
= 1 through absorption in active galactic nuclei and gamma-ray burst (GRB) afterglow spectra, allowing for the study of the evolution of these large-scale structures of the Universe. This work simulates WHIM filaments in the spectra of GRB X-ray afterglows with
Athena
using the SImulation of X-ray TElescopes framework. We investigate the feasibility of their detection with the X-IFU instrument, through O
VII
(
E
= 573 eV) and O
VIII
(
E
= 674 eV) absorption features, for a range of equivalent widths imprinted onto GRB afterglow spectra of observed starting fluxes ranging between 10
−12
and 10
−10
erg cm
−2
s
−1
, in the 0.3−10 keV energy band. The analyses of X-IFU spectra by blind line search show that
Athena
will be able to detect O
VII
−O
VIII
absorption pairs with EW
O
VII
> 0.13 eV and EW
O
VIII
> 0.09 eV for afterglows with
F
> 2 × 10
−11
erg cm
−2
s
−1
. This allows for the detection of ≈ 45−137 O
VII
−O
VIII
absorbers during the four-year mission lifetime. The work shows that to obtain an O
VII
−O
VIII
detection of high statistical significance, the local hydrogen column density should be limited at
N
H
< 8 × 10
20
cm
−2
.
We present results from the Nuclear Spectroscopic Telescope Array observations of the new black hole X-ray binary candidate MAXI J1631-479 at two epochs during its 2018-2019 outburst, which caught ...the source in a disk dominant state and a power-law dominant state. Strong relativistic disk reflection features are clearly detected, displaying significant variations in the shape and strength of the broad iron emission line between the two states. Spectral modeling of the reflection spectra reveals that the inner radius of the optically thick accretion disk evolves from <1.9 to 12 1 rg (statistical errors at 90% confidence level) from the disk dominant to the power-law dominant state. Assuming in the former case that the inner disk radius is consistent with being at the innermost stable circular orbit, we estimate a black hole spin of a* > 0.94. Given that the bolometric luminosity is similar in the two states, our results indicate that the disk truncation observed in MAXI J1631-479 in the power-law dominant state is unlikely to be driven by a global variation in the accretion rate. We propose that it may instead arise from local instabilities in the inner edge of the accretion disk at high accretion rates. In addition, we find an absorption feature in the spectra centered at 7.33 0.03 keV during the disk dominant state, which is evidence for the rare case that an extremely fast disk wind ( ) is observed in a low-inclination black hole binary, with the viewing angle of 29° 1° as determined by the reflection modeling.
Kilohertz quasi-periodic oscillations or kHz QPOs occur on the orbital timescale of the inner accretion flow, and may carry signatures of the physics of strong gravity (c2 GM/R) and possibly clues to ...constraining the neutron star equation of state. Both the timing behavior of kHz QPOs and the time-averaged spectra of these systems have been studied extensively, yet no model completely describes all the properties of kHz QPOs. Here, we present a systematic study of spectral-timing products of kHz QPOs from low-mass X-ray binary systems through the use of archival Rossi X-ray Timing Explorer/Proportional Counter Array data. For the lower kHz QPOs in 14 objects and the upper kHz QPOs in six objects, we were able to obtain correlated time lags as a function of QPO frequency and energy, as well as energy-dependent covariance spectra and intrinsic coherence. For the lower kHz QPOs, we find a monotonic decrease in lags with increasing energy, rising covariance to ∼12 keV, and near unity coherence at all energies. For the upper kHz QPOs, we find near zero lags, rising covariance to ∼12 keV, and less well-constrained coherence at all energies. These results suggest that while kHz QPOs are likely produced by similar mechanisms across the population of LMXBs, the lower kHz QPOs are likely produced by a different mechanism than the upper kHz QPOs.
Very few galactic nuclei are found to show significant X-ray quasi-periodic oscillations (QPOs). After carefully modeling the noise continuum, we find that the ~3.8 hr QPO in the ultrasoft active ...galactic nucleus candidate 2XMM J123103.2+110648 was significantly detected (~5sigma) in two XMM-Newton observations in 2005, but not in the one in 2003. The QPO root mean square (rms) is very high and increases from ~25% in 0.2-0.5 keV to ~50% in 1-2 keV. The QPO probably corresponds to the low-frequency type in Galactic black hole X-ray binaries, considering its large rms and the probably low mass (~105 M sub(middot in circle)) of the black hole in the nucleus. We also fit the soft X-ray spectra from the three XMM-Newton observations and find that they can be described with either pure thermal disk emission or optically thick low-temperature Comptonization. We see no clear X-ray emission from the two Swift observations in 2013, indicating lower source fluxes than those in XMM-Newton observations.
The ultraluminous X-ray (ULX) source ESO 243-49 HLX-1, which reaches a maximum luminosity of 1042 erg s--1 (0.2-10 keV), currently provides the strongest evidence for the existence of ...intermediate-mass black holes (IMBHs). To study the spectral variability of the source, we conduct an ongoing monitoring campaign with the Swift X-ray Telescope (XRT), which now spans more than two years. We found that HLX-1 showed two fast rise and exponential decay type outbursts in the Swift XRT light curve with increases in the count rate of a factor ~40 separated by 375 ? 13 days. We obtained new XMM-Newton and Chandra dedicated pointings that were triggered at the lowest and highest luminosities, respectively. From spectral fitting, the unabsorbed luminosities ranged from 1.9 X 1040 to 1.25 X 1042 erg s--1. We confirm here the detection of spectral state transitions from HLX-1 reminiscent of Galactic black hole binaries (GBHBs): at high luminosities, the X-ray spectrum showed a thermal state dominated by a disk component with temperatures of 0.26 keV at most, and at low luminosities the spectrum is dominated by a hard power law with a photon index in the range 1.4-2.1, consistent with a hard state. The source was also observed in a state consistent with the steep power-law state, with a photon index of ~3.5. In the thermal state, the luminosity of the disk component appears to scale with the fourth power of the inner disk temperature, which supports the presence of an optically thick, geometrically thin accretion disk. The low fractional variability (rms of 9% ? 9%) in this state also suggests the presence of a dominant disk. The spectral changes and long-term variability of the source cannot be explained by variations of the beaming angle and are not consistent with the source being in a super-Eddington accretion state as is proposed for most ULX sources with lower luminosities. All this indicates that HLX-1 is an unusual ULX as it is similar to GBHBs, which have non-beamed and sub-Eddington emission, but with luminosities three orders of magnitude higher. In this picture, a lower limit on the mass of the black hole of >9000 M can be derived, and the relatively low disk temperature in the thermal state also suggests the presence of an IMBH of a few 103 M .
We analyze 18 sources that showed interesting properties of periodicity, very soft spectra, and/or large long-term variability in X-rays in our project of classification of sources from the 2XMMi-DR3 ...catalog, but were poorly studied in the literature, in order to investigate their nature. Two hard sources show X-ray periodicities of ~1.62 hr (2XMM J165334.4-414423) and ~2.1 hr (2XMM J133135.2-315541) and are probably magnetic cataclysmic variables. One source, 2XMM J123103.2+110648, is an active galactic nucleus (AGN) candidate showing very soft X-ray spectra (kT ~ 0.1 keV) and exhibiting an intermittent ~3.8 hr quasi-periodic oscillation. There are six other very soft sources (with kT < 0.2 keV), which might be in other galaxies with luminosities between ~10 super(38)-10 super(42) erg s super(-1). They probably represent a diverse group that might include objects such as ultrasoft AGNs and cool thermal disk emission from accreting intermediate-mass black holes. Six highly variable sources with harder spectra are probably in nearby galaxies with luminosities above 10 super(37) erg s super(-1) and thus are great candidates for extragalactic X-ray binaries. One of them (2XMMi J004211.2+410429, in M31) is probably a new-born persistent source, having been X-ray bright and hard in 0.3-10 keV for at least four years since it was discovered entering an outburst in 2007. Three highly variable hard sources appear at low galactic latitudes and have maximum luminosities below ~10 super(34) erg s super(-1) if they are in our Galaxy. Thus, they are great candidates for cataclysmic variables or very faint X-ray transients harboring a black hole or neutron star. Our interpretations of these sources can be tested with future long-term X-ray monitoring and multi-wavelength observations.
We present the results of NuSTAR and XMM-Newton observations of the two ultraluminous X-ray sources: NGC 1313 X-1 and X-2. The combined spectral bandpass of the two satellites enables us to produce ...the first spectrum of X-1 between 0.3 and 30 keV, while X-2 is not significantly detected by NuSTAR above 10 keV. The NuSTAR data demonstrate that X-1 has a clear cutoff above 10 keV, whose presence was only marginally detectable with previous X-ray observations. This cutoff rules out the interpretation of X-1 as a black hole in a standard low/hard state, and it is deeper than predicted for the downturn of a broadened iron line in a reflection-dominated regime. The cutoff differs from the prediction of a single-temperature Comptonization model. Further, a cold disk-like blackbody component at ~0.3 keV is required by tire data, confirming previous measurements by XMM-Newton only. We observe a spectral transition in X-2, from a state with high luminosity and strong variability to a lower-luminosity state with no detectable variability, and we link this behavior to a transition from a super-Eddington to a sub-Eddington regime.
ABSTRACT
Accretion and ejection of matter in active galactic nuclei (AGNs) are tightly connected phenomena and represent fundamental mechanisms regulating the growth of the central supermassive black ...hole and the evolution of the host galaxy. However, the exact physical processes involved are not yet fully understood. We present a high-resolution spectral analysis of a simultaneous XMM–Newton and NuSTAR observation of the narrow line Seyfert 1 (NLS1) AGN 1H 1934-063, during which the X-ray flux dropped by a factor of ∼6 and subsequently recovered within 140 kiloseconds. By means of the time-resolved and flux-resolved X-ray spectroscopy, we discover a potentially variable warm absorber and a relatively stable ultra-fast outflow (UFO, $v_\mathrm{UFO}\sim -0.075\, c$) with a mild ionization state ($\log (\xi /\mathrm{erg\, cm\, s^{-1})}\sim 1.6$). The detected emission lines (especially a strong and broad feature around 1 keV) are of unknown origin and cannot be explained with emission from plasmas in photo- or collisional-ionization equilibrium. Such emission lines could be well described by a strongly blueshifted (z ∼ −0.3) secondary reflection off the base of the equatorial outflows, which may reveal the link between the reprocessing of the inner accretion flow photons and the ejection. However, this scenario although being very promising is only tentative and will be tested with future observations.
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