The origin of the iron fluorescent line at 6.4 keV from an extended region surrounding the Arches cluster is debated and the non-variability of this emission up to 2009 has favoured the low-energy ...cosmic ray origin over a possible irradiation by hard X-rays. By probing the variability of the Arches cloud non-thermal emission in the most recent years, including a deep observation in 2012, we intend to discriminate between the two competing scenarios. We perform a spectral fit of XMM–Newton observations collected from 2000 to 2013 in order to build the Arches cloud light curve corresponding to both the neutral Fe Kα line and the X-ray continuum emissions. We reveal a 30 per cent flux drop in 2012, detected with more than 4σ significance for both components. This implies that a large fraction of the studied non-thermal emission is due to the reflection of an X-ray transient source.
We present a comprehensive spectral analysis of all INTEGRAL data obtained so far for the X-ray-bright Seyfert galaxy NGC 4151. We also use all contemporaneous data from RXTE, XMM–Newton, Swift and ...Suzaku. We find a linear correlation between the medium- and hard-energy X-ray fluxes measured by INTEGRAL, which indicates an almost constant spectral index over 6 yr. The majority of INTEGRAL observations were made when the source was either at a very bright or very dim hard–X-ray state. We find that thermal Comptonization models applied to the bright state yields the plasma temperature of ≃50–70 keV and its optical depth of ≃1.3–2.6, depending on the assumed source geometry. For the dim state, these parameters are in the ranges of ≃180–230 keV and ≃0.3–0.7, respectively. The Compton parameter is for all the spectra, indicating a stable geometry. Using this result, we can determine the reflection effective solid angles associated with the close and distant reprocessing media as and , respectively. The plasma energy balance, the weak disc reflection and a comparison of the UV fluxes illuminating the plasma to the observed ones are all consistent with an inner hot accretion surrounded by an outer cold disc. The disc truncation radius can be determined from an approximate equipartition between the observed UV and X-ray emission, and from the fitted disc blackbody model, as ∼15 gravitational radii. Alternatively, our results can be explained by a mildly relativistic coronal outflow.
Aims. We present an update of the 3C 273's database hosted by the ISDC, completed with data from radio to gamma-ray observations over the last 10 years. We use this large data set to study the ...multiwavelength properties of this quasar, especially focussing on its variability behaviour. Methods. We study the amplitude of the variations and the maximum variability time scales across the broad-band spectrum and correlate the light curves in different bands, specifically with the X-rays, to search for possible connections between the emission at different energies. Results. 3C 273 shows variability at all frequencies, with amplitudes and time scales strongly depending on the energy and being the signatures of the different emission mechanisms. The variability properties of the X-ray band imply the presence of either two separate components (possibly a Seyfert-like and a blazar-like) or at least two parameters with distinct timing properties to account for the X-ray emission below and above ~20 keV. The dominant hard X-ray emission is most probably not due to electrons accelerated by the shock waves in the jet as their variability does not correlate with the flaring millimeter emission, but seems to be associated to long-timescale variations in the optical. This optical component is consistent with being optically thin synchrotron radiation from the base of the jet and the hard X-rays would be produced through inverse Compton processes (SSC and/or EC) by the same electron population. We show evidence that this synchrotron component extends from the optical to the near-infrared domain, where it is blended by emission of heated dust that we find to be located within about 1 light-year from the ultraviolet source.
Supplementing kindergarten children during a cold season with a prebiotic inulin-type fructans product with shorter and longer fructan chains has been shown to reduce febrile episodes requiring ...medical attention and to lower the incidence of sinusitis. These beneficial effects may be connected to the specific modulation of children’s gut microbiota. By applying quantitative and qualitative microbiota analysis this study aimed at characterising the gut microbiota composition and at exploring effects of prebiotic intervention on the gut microbiota during a 24-weeks intervention and during antibiotic treatment in healthy children. The study was a randomised, placebo-controlled trial with 258 healthy children aged 3 to 6 years consuming 6 g/day prebiotic inulin-type fructans or maltodextrin. During the course of the study, faecal samples were collected and subject to targeted qPCR analysis and phylogenetic profiling by multiplexed high throughput sequencing of the prokaryotic 16S rRNA gene PCR amplicons. The microbiota composition of the cohort could be clustered into three distinct constellations (enterotypes). Prebiotic intake resulted in a selective modulation of the gut microbiota composition. Relative abundance of Bifidobacterium was significantly higher in the prebiotic group (n=104) compared to control group (n=105) and this effect was found for all three enterotypes. Antibiotic administration decreased the relative abundance of Bifidobacterium in both groups. Nonetheless, children of the prebiotic group receiving antibiotic treatment displayed significantly higher levels of Bifidobacterium than children receiving the placebo control. Prebiotic supplementation induced specific changes in the gut microbiota composition of children aged 3 to 6 years. Moreover, it attenuated antibiotic-induced disturbances in the gut microbiota composition as shown by higher relative abundance of bifidobacteria at the end of the antibiotic treatment in the prebiotic group. With the previously reported benefits on immune function, the study contributes to the evidence on the immune-modulating effects of prebiotics through gut microbiota modifications. The study was registered as NCT03241355 (https://clinicaltrials.gov/show/NCT03241355).
Aims. Multiwavelength variability of blazars offers indirect, but very effective, insight into their powerful engines and on the mechanisms through which energy is propagated from the centre down the ...jet. The BL Lac object Mkn 421 is a TeV emitter, a bright blazar at all wavelengths, and therefore an excellent target for variability studies. Methods. We activated INTEGRAL observations of Mkn 421 in an active state on 16–21 April 2013, and complemented them with Fermi-LAT data. Results. We obtained well sampled optical, soft, and hard X-ray light curves that show the presence of two flares and time-resolved spectra in the 3.5–60 keV (JEM-X and IBIS/ISGRI) and 0.1–100 GeV (Fermi-LAT) ranges. The average flux in the 20–100 keV range is 9.1 × 10-11 erg s-1 cm-2 (~4.5 mCrab) and the nuclear average apparent magnitude, corrected for Galactic extinction, is V ≃ 12.2. In the time-resolved X-ray spectra, which are described by broken power laws and, marginally better, by log-parabolic laws, we see a hardening that correlates with flux increase, as expected in refreshed energy injections in a population of electrons that later cool via synchrotron radiation. The hardness ratios between the JEM-X fluxes in two different bands and between the JEM-X and IBIS/ISGRI fluxes confirm this trend. During the observation, the variability level increases monotonically from the optical to the hard X-rays, while the large LAT errors do not allow a significant assessment of the MeV-GeV variability. The cross-correlation analysis during the onset of the most prominent flare suggests a monotonically increasing delay of the lower frequency emission with respect to that at higher frequency, with a maximum time-lag of about 70 min, that is however not well constrained. The spectral energy distributions from the optical to the TeV domain were compared to homogeneous models of blazar emission based on synchrotron radiation and synchrotron self-Compton scattering. They represent a satisfactory description, except in the state corresponding to the LAT softest spectrum and highest flux. Conclusions. Multiwavelength variability of Mkn 421 can be very complex, with patterns changing from epoch to epoch down to intra-day timescales, depending on the emission state. This makes accurate monitoring of this source during bright hard X-ray states necessary and calls for the elaboration of multicomponent, multizone, time-dependent models.
We have compiled a complete extragalactic sample based on 625,000 deg super(2) to a limiting flux of 3 x 10 super(-11) ergs cm super(-2) s super(-1) (67000 deg super(2) to a flux limit of 10 ...super(-11) ergs cm super(-2) s super(-1)) in the 20-40 keV band with INTEGRAL. We have constructed a detailed exposure map to compensate for effects of nonuniform exposure. The flux-number relation is best described by a power law with a slope of a = 1.66 c 0.11. The integration of the cumulative flux per unit area leads to f sub(20-40 keV) = 2.6 x 10 super(-10) ergs cm super(-2) s super(-1) sr super(-1), which is about 1% of the known 20-40 keV X-ray background. We present the first luminosity function of AGNs in the 20-40 keV energy range, based on 38 extragalactic objects detected by the imager IBIS-ISGRI on board INTEGRAL. The luminosity function shows a smoothly connected double-power-law form with an index of g sub(1) = 0.8 below and g sub(2) = 2.1 above the turnover luminosity of L sub(*) = 2.4 x 10 super(43) ergs s super(-1). The emissivity of all INTEGRAL AGNs per unit volume is W sub(20-40 keV) (> 10 super(41) ergs s super(-1)) = 2.8 x 10 super(38) ergs s super(-1) h super(3) sub(70) Mpc super(-3). These results are consistent with those derived in the 2-20 keV energy band and do not show a significant contribution by Compton-thick objects. Because the sample used in this study is truly local ( = 0.022), only limited conclusions can be drawn for the evolution of AGNs in this energy band.
The First INTEGRAL AGN Catalog Beckmann, V; Gehrels, N; Shrader, C. R ...
The Astrophysical journal,
02/2006, Letnik:
638, Številka:
2
Journal Article
Recenzirano
We present the first INTEGRAL AGN catalog, based on observations performed from launch of the mission in 2002 October until 2004 January. The catalog includes 42 AGNs, of which 10 are Seyfert 1, 17 ...are Seyfert 2, and 9 are intermediate Seyfert 1.5. The fraction of blazars is rather small, with five detected objects, and only one galaxy cluster and no starburst galaxies have been detected so far. A complete subset consists of 32 AGNs with a significance limit of 7 s in the INTEGRAL ISGRI 20-40 keV data. Although the sample is not flux limited, the distribution of sources shows a ratio of obscured to unobscured AGNs of 1.5-2.0, consistent with luminosity-dependent unified models for AGNs. Only four Compton-thick AGNs are found in the sample. Based on the INTEGRAL data presented here, the Seyfert 2 spectra are slightly harder ( = 1.95 c 0.01) than Seyfert 1.5 ( = 2.10 c 0.02) and Seyfert 1 ( = 2.11 c 0.05).
ABSTRACT We present analysis results on the Seyfert2 galaxy NGC4388 based on 6yr of INTEGRAL data combined with Swift/Burst Alert Telescope survey and Swift/X-Ray Telescope pointed observations. ...These data, taken from 2003 to 2009, allow us to study the broad-band properties of this active galactic nucleus in the 0.3-300keV energy range. The continuum emission of NGC4388 is well represented by an absorbed power-law model with exponential cut-off at high energies and an upper limit on the reflection component of R < 0.5. We find slow strong variations of the hard X-ray emission, indicating both flux and spectral slope changes on the 3-6months time-scale. In comparison with previous results on NGC4388, the source shows a complex variability behaviour, i.e. the spectral shape and the 20-60keV flux vary independently. PUBLICATION ABSTRACT
We present analysis results on the Seyfert 2 galaxy NGC 4388 based on 6 yr of INTEGRAL data combined with Swift/Burst Alert Telescope survey and Swift/X-Ray Telescope pointed observations. These ...data, taken from 2003 to 2009, allow us to study the broad-band properties of this active galactic nucleus in the 0.3-300 keV energy range. The continuum emission of NGC 4388 is well represented by an absorbed power-law model with exponential cut-off at high energies and an upper limit on the reflection component of R < 0.5. We find slow strong variations of the hard X-ray emission, indicating both flux and spectral slope changes on the 3-6 months time-scale. In comparison with previous results on NGC 4388, the source shows a complex variability behaviour, i.e. the spectral shape and the 20-60 keV flux vary independently.
In Spring 2005, the blazar 3C 454.3 underwent a dramatic outburst at all wavelengths from mm to X-rays. This prompted INTEGRAL observations, accomplished in 15-18 May 2005. The source was detected ...by the INTEGRAL instruments from 3 to 200 keV in a bright state (${\sim} 5 \times 10^{-10}$ erg s-1 cm-2), at least a factor of 2-3 higher than previously observed. This is one of the brightest blazar detections achieved by INTEGRAL. During the 2.5 days of INTEGRAL monitoring, we detected a ~20% decrease in the hard X-rays (20-40 keV), indicating that we have sampled the decaying part of the flare. The decrease is less apparent in the soft X-rays (5-15 keV). The simultaneous optical variations are weakly correlated with those at soft X-rays, and not clearly correlated with those at hard X-rays. The spectral energy distribution exhibits two components, as typically seen in blazars, which can be modeled with synchrotron radiation and inverse Compton scattering occurring in a region external to the broad line region.
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