X-ray spectra of active galactic nuclei (AGN) are usually described as power law spectra, characterized by the spectral slope α or photon index Γ. Here we discuss the X-ray spectral properties within ...the framework of clumpy accretion flows, and estimate the power law slope as a function of the source parameters. We expect harder spectra in massive objects than in less massive sources, and steeper spectra in higher accretion rate systems. The predicted values of the photon index cover the range of spectral slopes typically observed in Seyfert galaxies and quasars. The overall trends are consistent with observations, and may account for the positive correlation of the photon index with Eddington ratio (and the possible anticorrelation with black hole mass) observed in different AGN samples. Spectral properties are also closely related to variability properties. We obtain that shorter characteristic time scales are associated with steeper spectra. This agrees with the observed “spectral-timing” correlation.
Context.In its first 4 years of observing the sky above 20 keV, INTEGRAL-ISGRI has detected 500 sources, around half of which are new or unknown at these energies. Follow-up observations at other ...wavelengths revealed that some of these sources feature unusually large column densities, long pulsations, and other interesting characteristics. Aims.We investigate where new and previously-known sources detected by ISGRI fit in the parameter space of high-energy objects, and we use the parameters to test correlations expected from theoretical predictions. For example, the influence of the local absorbing matter on periodic modulations is studied for Galactic High-Mass X-ray Binaries (HMXBs) with OB supergiant and Be companions. We examine the spatial distribution of different types of sources in the Milky Way using various projections of the Galactic plane, in order to highlight signatures of stellar evolution and to speculate on the origin of the group of sources whose classifications are still uncertain. Methods.Parameters that are available in the literature, such as positions, photoelectric absorption ($N_{{\rm H}}$), spin and orbital periods, and distances or redshifts, were collected for all sources detected by ISGRI. These values and their references are provided online. Results.ISGRI has detected similar numbers of X-ray Binaries and Active Galactic Nuclei (AGN). The former group contains new members of the class of HMXBs with supergiant stellar companions. Usually, this type of object presents strong intrinsic absorption which leads to a peak emission in an energy range that ISGRI is ideally suited to detect. Thanks to these additional systems, we are able to show that HMXBs are generally segregated in plots of intrinsic $N_{{\rm H}}$ versus the orbital period of the system and versus the spin period of the pulsar, based on whether the companion is a Be or an OB supergiant star. We also find a tentative but expected anti-correlation between $N_{{\rm H}}$ and the orbital period, and a possible and unexpected correlation between the $N_{{\rm H}}$ and the spin period. While only a handful of new Low-Mass X-ray Binaries (LMXBs) have been discovered, there are many sources that remain unclassified and they appear to follow a spatial distribution typical of Galactic sources (especially LMXBs) rather than extragalactic sources.
The second INTEGRAL AGN catalogue Beckmann, V.; Soldi, S.; Ricci, C. ...
Astronomy and astrophysics (Berlin),
10/2009, Volume:
505, Issue:
1
Journal Article
Peer reviewed
Open access
Aims. The INTEGRAL mission provides a large data set for studying the hard X-ray properties of AGN and allows testing of the unified scheme for AGN. Methods. We present analysis of ...INTEGRAL IBIS/ISGRI, JEM-X, and OMC data for 199 AGN supposedly detected by INTEGRAL above 20 keV. Results. The data analysed here allow significant spectral extraction on 148 objects and an optical variability study of 57 AGN. The slopes of the hard X-ray spectra of Seyfert 1 and Seyfert 2 galaxies are found to be consistent within the uncertainties, whereas higher cut-off energies and lower luminosities we measured for the more absorbed/type 2 AGN. The intermediate Seyfert 1.5 objects exhibit hard X-ray spectra consistent with those of Seyfert 1. When applying a Compton reflection model, the underlying continua appear the same in Seyfert 1 and 2 with Γ $\simeq$ 2, and the reflection strength is about R $\simeq$ 1, when assuming different inclination angles. A significant correlation is found between the hard X-ray and optical luminosity and the mass of the central black hole in the sense that the more luminous objects appear to be more massive. There is also a general trend toward the absorbed sources and type 2 AGN having lower Eddington ratios. The black hole mass appears to form a fundamental plane together with the optical and X-ray luminosity of the form $L_V \propto L_{\rm X}^{0.6} M_{\rm BH}^{0.2}$, similar to what is found between $L_{\it R}$, LX, and MBH. Conclusions. The transition from the type 1 to type 2 AGN appears to be smooth. The type 2 AGN are less luminous and have less accreting super massive black holes. The unified model for Seyfert galaxies seems to hold, showing in hard X-rays that the central engine is the same in Seyfert 1 and 2, but seen under different inclination angles and absorption. The fundamental plane links the accretion mechanism with the bulge of the host galaxy and with the mass of the central engine in the same way in all types of Seyfert galaxies.
Aims.The Galactic bulge region is a rich host of variable high-energy point sources. Since 2005, February 17 we are monitoring the source activity in the Galactic bulge region regularly and ...frequently, i.e., about every three days, with the instruments onboard INTEGRAL. Thanks to the large field of view, the imaging capabilities and the sensitivity at hard X-rays, we are able to present for the first time a detailed homogeneous (hard) X-ray view of a sample of 76 sources in the Galactic bulge region. Methods.We describe the successful monitoring program and show the first results from the start of the monitoring up to 2006, April 21, i.e., for a period of about one and a half year, during three visibility seasons. We focus on the short (hour), medium (month) and long-term (year) variability in the hard X-ray bands, i.e., 20-60 keV and 60-150 keV. When available, we discuss the simultaneous observations in the soft X-ray, 3-10 keV and 10-25 keV, bands. Results.Almost all the sources in the Galactic bulge region we detect in the 20-60 keV and 60-150 keV bands are variable. During the last two and a half weeks of the third visibility season most of the known persistent (hard) X-ray sources in the Galactic Center region were not detected. Of our sample of sources, per visibility season we detect 32/33 sources in the 20-60 keV band and 8/9 sources in the 60-150 keV band above a signal to noise of 7. On average, we find per visibility season one active bright ($\ga$100 mCrab, 20-60 keV) black-hole candidate X-ray transient and three active weaker ($\la$25 mCrab, 20-60 keV) neutron star X-ray transients. Most of the time a clear anti-correlation can be seen between the soft and hard X-ray emission in some of the X-ray bursters. Hard X-ray flares or outbursts in X-ray bursters, which have a duration of the order of weeks are accompanied by soft X-ray drops. On the other hand, hard X-ray drops can be accompanied by soft X-ray flares/outbursts. During the course of our program we found a number of new sources, IGR J17354-3255, IGR 17453-2853, IGR J17454-2703, IGR J17456-2901b, IGR J17536-2339, and IGR J17541-2252. We report here on some of the high-energy properties of these sources. Conclusions.The high-energy light curves of all the sources in the field of view, and the high-energy images of the region, are made available through the WWW, as soon as possible after the observations have been performed, at http://isdc.unige.ch/Science/BULGE/.
Aims.We studied and compared the long-term average hard X-ray (>20 keV) spectra of a sample of twelve bright low-mass X-ray binaries hosting a neutron star (NS). Our sample comprises the six well ...studied Galactic Z sources and six Atoll sources, four of which are bright (“GX”) bulge sources while two are weaker ones in the 2–10 keV range (H 1750–440 and H 1608–55). Methods.For all the sources of our sample, we analysed available public data and extracted average spectra from the IBIS/ISGRI detector on board INTEGRAL. Results.We can describe all the spectral states in terms of the bulk motion Comptonisation scenario. We find evidence that bulk motion is always present, its strength is related to the accretion rate and it is suppressed only in the presence of high local luminosity. The two low-dim Atoll source spectra are dominated by photons up-scattered presumably due to dynamical and thermal Comptonisation in an optically thin, hot plasma. For the first time, we extend the detection of H 1750–440 up to 150 keV. The Z and bright “GX” Atoll source spectra are very similar and are dominated by Comptonised blackbody radiation of seed photons, presumably coming from the accretion disc and NS surface, in an optically thick cloud with plasma temperature in the range of 2.5–3 keV. Six sources show a hard tail in their average spectrum: Cyg X-2 (Z), GX 340+0 (Z), GX 17+2 (Z), GX 5–1 (Z), Sco X–1 (Z) and GX 13+1 (Atoll). This is the first detection of a hard tail in the X-ray spectrum of the peculiar GX 13+1. Using radio data from the literature we find, in all Z sources and bright “GX” Atolls, a systematic positive correlation between the X-ray hard tail (40–100 keV) and the radio luminosity. This suggests that hard tails and energetic electrons causing the radio emission may have the same origin, most likely the Compton cloud located inside the NS magnetosphere.
X-ray variability of active galactic nuclei (AGN) and black hole binaries can be analysed by means of the power spectral density (PSD). The break observed in the power spectrum defines a ...characteristic variability timescale of the accreting system. The empirical variability scaling that relates characteristic timescale, black hole mass, and accretion rate (\hbox{$T_{\rm B} \propto M_{\rm BH}^{2.1}/\dot{M}^{0.98}$}TB∝MBH2.1/Ṁ0.98) extends from supermassive black holes in AGN down to stellar-mass black holes in binary systems. We suggest that the PSD break timescale is associated with the cooling timescale of electrons in the Comptonisation process at the origin of the observed hard X-ray emission. We find that the Compton cooling timescale directly leads to the observational scaling and naturally reproduces the functional dependence on black hole mass and accretion rate (\hbox{$t_{\rm C} \propto M_{\rm BH}^{2}/\dot{M}$}tC∝MBH2/Ṁ). This result simply arises from general properties of the emission mechanism and is independent of the details of any specific accretion model.
Abstract
Although residential environment might be an important predictor of depression among older adults, systematic reviews point to a lack of longitudinal investigations, and the generalizability ...of the findings is limited to a few countries. We used longitudinal data collected between 2012 and 2017 in 3 surveys including 15 European countries and the United States and comprising 32,531 adults aged 50 years or older. The risk of depression according to perceived neighborhood disorder and lack of social cohesion was estimated using 2-stage individual-participant-data meta-analysis; country-specific parameters were analyzed by meta-regression. We conducted additional analyses on retired individuals. Neighborhood disorder (odds ratio (OR) = 1.25) and lack of social cohesion (OR = 1.76) were significantly associated with depression in the fully adjusted models. In retirement, the risk of depression was even higher (neighborhood disorder: OR = 1.35; lack of social cohesion: OR = 1.93). Heterogeneity across countries was low and was significantly reduced by the addition of country-level data on income inequality and population density. Perceived neighborhood problems increased the overall risk of depression among adults aged 50 years or older. Policies, especially in countries with stronger links between neighborhood and depression, should focus on improving the physical environment and supporting social ties in communities, which can reduce depression and contribute to healthy aging.
Aims. We present the first detailed X-ray analysis of three active galactic nuclei, the Seyfert 1 galaxies UGC 3142 and ESO 140-43, and the Seyfert 2 galaxy ESO 383-18, to study the geometry and the ...physical characteristics of their absorbers. Methods. High-quality XMM-Newton EPIC and RGS data were analyzed as well as Swift/XRT and BAT and INTEGRAL IBIS/ISGRI data to cover the 0.3-110 keV energy range. For ESO 140-43 also XMM-Newton/OM and Swift/UVOT data were used. We studied the variability of the three AGN on a time-scale of seconds using the EPIC/PN light curves, and the long-term time-scale variability of ESO 140-43 using two observations performed six months apart by XMM-Newton. Results. The spectra of the three Seyfert galaxies present a “soft excess” at energies E < 2 keV above a power law continuum that can be modeled by complex absorption, without any additional emission component. The X-ray sources in UGC 3142 and ESO 383-18 are absorbed by two layers of neutral material, with covering fractions f1 $\simeq$ 0.92 and f2 $\simeq$ 0.57 for UGC 3142, and f1 $\simeq$ 0.97 and f2 $\simeq$ 0.86 for ESO 383-18. While the clumpy absorber could be part of a disk wind or of the broad line region for UGC 3142, for ESO 383-18 a clumpy torus plus Compton thin dust lanes are more likely. The spectra of ESO 140-43 can be well fitted with a power law absorbed by three clumpy ionized absorbers with different covering factors, column densities, and ionization parameters, likely part of a moving clumpy system, which could be a disk wind or the broad line region. The strong spectral and flux variability on a time-scale of six months seen in ESO 140-43 is likely due to changes in the moving absorbers. We were able to detect the variation of the covering factor of one of the three ionized absorbers on a kilo-seconds time-scale in the EPIC light-curve of ESO 140-43.
An analysis of the high-energy emission from IGR J16393-4643 (=AX J1639.0-4642) is presented using data from INTEGRAL and XMM-Newton. The source is persistent in the 20–40 keV band at an average flux ...of $5.1\times10^{-11}$ erg cm-2 s-1, with variations in intensity by at least an order of magnitude. A pulse period of 912.0±0.1 s was discovered in the ISGRI and EPIC light curves. The source spectrum is a strongly-absorbed ($N_{\mathrm{H}}=(2.5\pm0.2)\times10^{23}$ cm-2) power law that features a high-energy cutoff above 10 keV. Two iron emission lines at 6.4 and 7.1 keV, an iron absorption edge ≳7.1 keV, and a soft excess emission of $7\times10^{-15}$ erg cm-2 s-1 between 0.5–2 keV, are detected in the EPIC spectrum. The shape of the spectrum does not change with the pulse. Its persistence, pulsation, and spectrum place IGR J16393-4643 among the class of heavily-absorbed HMXBs. The improved position from EPIC is RA (J2000$)=16^{\mathrm{h}}39^{\mathrm{m}}05.4^{\mathrm{s}}$ and $\rm Dec=-46^{\circ}42'12''$ ($4''$ uncertainty) which is compatible with that of 2MASS J16390535-4642137.
Using the Chandra Advanced CCD Imaging Spectrometer Imaging array (ACIS-I), we have carried out a deep hard X-ray observation of the Galactic plane region at (l,b) - (28.5,0.0), where no discrete ...X-ray source had been reported previously. We have detected 274 new point X-ray sources (4 s confidence), as well as strong Galactic diffuse emission within two partially overlapping ACIS-I fields (6250 arcmin super(2) in total). The point-source sensitivity was 63 x 10 super(-15) ergs s super(-1) cm super(-2) in the hard X-ray band (2-10 keV) and 62 x 10 super(-16) ergs s super(-1) cm super(-2) in the soft band (0.5-2 keV). The sum of all the detected point-source fluxes accounts for only 610% of the total X-ray flux in the field of view. Even hypothesizing a new population of much dimmer and numerous Galactic point sources, the total observed X-ray flux cannot be explained. Therefore, we conclude that X-ray emission from the Galactic plane has a truly diffuse origin. Removing point sources brighter than 63 x 10 super(-15) ergs s super(-1) cm super(-2) (2-10 keV), we have determined the Galactic diffuse X-ray flux to be 6.5 x 10 super(-1) ergs s super(-1) cm super(-2) deg super(-2) (2-10 keV). Only 26 point sources were detected in both the soft and hard bands, indicating that there are two distinct classes of X-ray sources distinguished by their spectral hardness ratios. The surface number density of the hard sources is only slightly higher than that measured at the high Galactic latitude regions, indicating that the majority of the hard sources are background AGNs. Following up the Chandra observation, we have performed a near-infrared (NIR) survey with SofI at ESO/NTT. Almost all the soft X-ray sources have been identified in the NIR, and their spectral types are consistent with main-sequence stars, suggesting that most of them are nearby X-ray-active stars. On the other hand, only 22% of the hard sources had NIR counterparts, which are presumably Galactic. From X-ray and NIR spectral study, they are most likely to be quiescent cataclysmic variables. Our observation suggests a population of 10 super(4) cataclysmic variables in the entire Galactic plane fainter than 62 x 10 super(33) ergs s super(-1). We have carried out a precise spectral study of the Galactic diffuse X-ray emission excluding the point sources. Confirming previous results, we have detected prominent emission lines from highly ionized heavy elements in the diffuse emission. In particular, the central energy of the iron emission line was determined to be 6.52 super(+) sub(-) super(0) sub(0) super(.) sub(.) super(0) sub(1) super(8) sub(4) keV (90% confidence), which is significantly lower than what is expected from a plasma in thermal equilibrium. The downward shift of the iron line center energy suggests nonequilibrium ionization states of the plasma or the presence of a nonthermal process to produce 6.4 keV fluorescent lines.
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