Abstract We present an analysis of NuSTAR X-ray observations of three active galactic nuclei (AGN) that were identified as candidate subparsec binary supermassive black hole (SMBH) systems in the ...Catalina Real-Time Transient Survey based on apparent periodicity in their optical light curves. Simulations predict that close-separation accreting SMBH binaries will have different X-ray spectra than single accreting SMBHs. We previously observed these AGN with Chandra and found no differences between their low-energy X-ray properties and the larger AGN population. However, some models predict differences to be more prominent at energies higher than probed by Chandra. We find that even at the higher energies probed by NuSTAR, the spectra of these AGN are indistinguishable from the larger AGN population. This could rule out models predicting large differences in the X-ray spectra in the NuSTAR bands. Alternatively, it might mean that these three AGN are not binary SMBHs.
We study the soft excess variability of the narrow line Seyfert 1 galaxy IRAS 13224–3809. We considered all five archival XMM-Newton observations, and we applied the flux–flux plot (FFP) method. We ...found that the FFPs were highly affected by the choice of the light curves’ time bin size, most probably because of the fast and large amplitude variations, and the intrinsic non-linear flux–flux relations in this source. Therefore, we recommend that the smallest bin-size should be used in such cases. Hence, We constructed FFPs in 11 energy bands below 1.7 keV, and we considered the 1.7–3 keV band, as being representative of the primary emission. The FFPs are reasonably well fitted by a “power-law plus a constant” model. We detected significant positive constants in three out of five observations. The best-fit slopes are flatter than unity at energies below ~0.9 keV, where the soft excess is strongest. This suggests the presence of intrinsic spectral variability. A power-law-like primary component, which is variable in flux and spectral slope (as \hbox{$\Gamma\propto N_{\rm PL}^{0.1}$}Γ∝NPL0.1) and a soft-excess component, which varies with the primary continuum (as \hbox{$F_{\rm excess}\propto F_{\rm primary}^{0.46}$}Fexcess∝Fprimary0.46), can broadly explain the FFPs. In fact, this can create positive “constants”, even when a stable spectral component does not exist. Nevertheless, the possibility of a stable, soft-band constant component cannot be ruled out, but its contribution to the observed 0.2–1 keV band flux should be less than ~15%. The model constants in the FFPs were consistent with zero in one observation, and negative at energies below 1 keV in another. It is hard to explain these results in the context of any spectral variability scenario, but they may signify the presence of a variable, warm absorber in the source.
Aims.
We develop a new physical model for the broadband spectral energy distribution (SED) of X-ray illuminated accretion discs that takes into account the mutual interaction of the accretion disc ...and the X-ray corona, including all the relativistic effects induced by the strong gravity of the central black hole (BH) on light propagation and on the transformation of the photon energy, from the disc to or from the corona rest-frames, and to the observer.
Methods.
We assumed a Keplerian optically thick and geometrically thin accretion disc and an X-ray source in the lamp-post geometry. The X-ray corona emits an isotropic, power-law-like X-ray spectrum, with a high-energy cut-off. We also assumed that all the energy that would be released by thermal radiation in the standard disc model in its innermost part is transported to the corona, effectively cooling the disc in this region. In addition, we include the disc heating due to thermalisation of the absorbed part of the disc illumination by the X-ray source. X-ray reflection due to the disc illumination is also included. The X-ray luminosity is given by the energy extracted from the accretion disc (or an external source) and the energy brought by the scattered photons themselves, thus energy balance is preserved. We computed the low-energy X-ray cut-off through an iterative process, taking full account of the interplay between the X-ray illumination of the disc and the resulting accretion disc spectrum that enters the corona. We also computed the corona radius, taking the conservation of the photon number during Comptonisation into account.
Results.
We discuss in detail the model SEDs and their dependence on the parameters of the system. We show that the disc-corona interaction has profound effects on the resultant SED, it constrains the X-ray luminosity and changes the shape and normalisation of the UV blue bump. We also compare the model SEDs with those predicted from similar models currently available. We use the new code to fit the broadband SED of NGC 5548, which is a typical Seyfert 1 galaxy. When combined with the results from previous model fits to the optical and UV time-lags of the same source, we infer a high black-hole spin, an intermediate system inclination, and an accretion rate below 10% of Eddington. The X-ray luminosity in this source could be supported by 45–70% of the accretion energy dissipated in the disc. The new model, named
KYNSED
, is publicly available to be used for fitting AGN SEDs inside the
XSPEC
spectral analysis tool.
Conclusions.
X-ray illumination of the accretion disc in AGN can explain both the observed UV and optical time-lags and the broadband SED of at least one AGN, namely NGC 5548. A simultaneous study of the optical, UV, and X-ray spectral and timing properties of these AGN with multiwavelength, long monitoring observations in the past few years will allow us to investigate the X-ray and disc geometry in these systems, and to constrain their physical parameters.
We present an analysis of the joint XMM-Newton and NuSTAR observations of the radio-quiet quasar QSO B2202-209. Using an optical observation from the Hale Telescope at the Palomar Observatory, we ...revise the redshift of the source from the previously reported z = 1.77 to z = 0.532, and we estimate the mass of the central black hole, log...(M sub( BH)/M...) = 9.08 plus or minus 0.18. The X-ray spectrum of this source can be well described by a power law of photon index ... = 1.82 plus or minus 0.05 with E sub( cut)=152... keV, in the rest frame of the source. Assuming a Comptonization model, we estimate the coronal temperature to be kT sub( e) = 42 plus or minus 3...keV and kT sub( e) = 56 plus or minus 3 keV for a spherical and a slab geometry, respectively. The coronal properties are comparable to the ones derived for local active galactic nuclei, despite a difference of around one order of magnitude in black hole mass and X-ray luminosity (L sub( 2 - 10) = 1.93 x 10 super( 45) erg s super( -1)). The quasar is X-ray loud, with an unusually flat observed optical-to-X-ray spectral slope ... = 1.00 plus or minus 0.02, and has an exceptionally strong optical Oiii line. Assuming that both the X-ray emission and the Oiii line are isotropic, these two extreme properties can be explained by a nearly edge-on disc, leading to a reduction in the observed ultraviolet continuum light. (ProQuest: ... denotes formulae/symbols omitted.)
Context.
The X-ray Integral Field Unit (X-IFU) is the high resolution X-ray spectrometer of ESA’s
Athena
X-ray observatory. It will deliver X-ray data in the 0.2–12 keV band with an unprecedented ...spectral resolution of 2.5 eV up to 7 keV. During the observation of very bright X-ray sources the X-IFU detectors will receive high photon rates. The count rate capability of the X-IFU will be improved by using the defocusing option, which will enable the observations of extremely bright sources with fluxes up to ≃1 Crab. In the defocused mode, the point spread function (PSF) of the telescope will be spread over a large number of pixels. In this case each pixel receives a small fraction of the overall flux. Due to the energy dependence of the PSF, this mode will generate energy-dependent artefacts increasing with count rate if not analysed properly. To account for the degradation of the energy resolution with pulse separation in a pixel, a grading scheme (of four grades) will be defined to realize the proper energy response to each event. This will create selection effects preventing the use of the nominal auxiliary response file (ARF) for all events.
Aims.
We present a new method for the reconstruction of the spectra obtained from observations performed with a PSF that varies as a function of energy. We apply our method to the case of the X-IFU spectra obtained during the defocused observations.
Methods.
We used the end-to-end SIXTE simulator to model defocused X-IFU observations. Then we estimated a new ARF for each of the grades by calculating the effective area at the level of each pixel.
Results.
Our method allows us to successfully reconstruct the spectra of bright sources when employed in the defocused mode, without any bias. Finally, we address how various sources of uncertainty related to our knowledge of the PSF as a function of energy affect our results.
Context.
Quasi-periodic eruptions (QPEs) are repeating thermal X-ray bursts associated with accreting massive black holes, the precise underlying physical mechanisms of which are still unclear.
Aims.
...We present a new candidate QPE source, AT 2019vcb (nicknamed Tormund by the
Zwicky
Transient Facility Collaboration), which was found during an archival search for QPEs in the
XMM-Newton
archive. It was first discovered in 2019 as an optical tidal disruption event (TDE) at
z
= 0.088, and its X-ray follow-up exhibited QPE-like properties. Our goals are to verify its robustness as QPE candidate and to investigate its properties to improve our understanding of QPEs.
Methods.
We performed a detailed study of the X-ray spectral behaviour of this source over the course of the
XMM-Newton
archival observation. We also report on recent
Swift
and NICER follow-up observations to constrain the source’s current activity and overall lifetime, as well as an optical spectral follow-up.
Results.
The first two
Swift
detections and the first half of the 30 ks
XMM-Newton
exposure of Tormund displayed a decaying thermal emission typical of an X-ray TDE. However, the second half of the exposure showed a dramatic rise in temperature (from 53.5
−7.7
+9.2
eV to 113.8
−2.7
+2.9
eV) and 0.2–2 keV luminosity (from 3.2
−1.0
+1.6
× 10
42
erg s
−1
to 1.19
−0.05
+0.05
× 10
44
erg s
−1
) over ∼15 ks. The late-time NICER follow-up indicates that the source is still X-ray bright more than three years after the initial optical TDE.
Conclusions.
Although only a rise phase was observed, Tormund’s strong similarities with a known QPE source (eRO-QPE1) and the impossibility to simultaneously account for all observational features with alternative interpretations allow us to classify Tormund as a candidate QPE. If confirmed as a QPE, it would further strengthen the observational link between TDEs and QPEs. It is also the first QPE candidate for which an associated optical TDE was directly observed, constraining the formation time of QPEs.
We study the X-ray spectra of a sample of 19 obscured, optically selected Seyfert galaxies (Sy 1.8, 1.9, and 2) in the local universe (d ≤ 175 Mpc), drawn from the CfA Seyfert sample. Our analysis is ...driven by the high sensitivity of NuSTAR in the hard X-rays, coupled with soft X-ray spectra using XMM-Newton, Chandra, Suzaku, and Swift/XRT. We also analyze the optical spectra of these sources in order to obtain accurate mass estimates and Eddington fractions. We employ four different models to analyze the X-ray spectra of these sources, which all provide consistent results. We find that 79%-90% of the sources are heavily obscured with line-of-sight column density NH > 1023 cm−2. We also find a Compton-thick (NH > 1024 cm−2) fraction of 37%-53%. These results are consistent with previous estimates based on multiwavelength analyses. We find that the fraction of reprocessed to intrinsic emission is positively correlated with NH and negatively correlated with the intrinsic, unabsorbed X-ray luminosity (in agreement with the Iwasawa-Taniguchi effect). Our results support the hypothesis that radiation pressure regulates the distribution of the circumnuclear material.
In this paper, we present an updated version of our model (KYNXiltr) which considers thermal reverberation of a standard Novikov-Thorne accretion disc illuminated by an X-ray point-like source. ...Previously, the model considered only two cases of black hole spins, and assumed a colour correction factor \(f_{\rm col} = 2.4\). Now, we extend the model to any spin value and colour correction. In addition, we consider two scenarios of powering the X-ray corona, either via accretion, or external to the accretion disc. We use KYNXiltr to fit the observed time lags obtained from intense monitoring of four local Seyfert galaxies (NGC 5548, NGC 4395, Mrk 817, and Fairall 9). We consider various combinations of black hole spin, colour correction, corona height, and fraction of accretion power transferred to the corona. The model fits well the overall time-lags spectrum in these sources (for a large parameter space). For NGC 4593 only, we detect a significant excess of delays in the U-band. The contribution of the diffuse BLR emission in the time-lags spectrum of this source is significant. It is possible to reduce the large best-fitting parameter space by combining the results with additional information, such as the observed Eddington ratio and average X-ray luminosity. We also provide an update to the analytic expression provided by Kammoun et al., for an X-ray source that is not powered by the accretion process, which can be used for any value of colour correction, and for two values of the black hole spin (0 and 0.998).
Interleukin-18 (IL-18) is activated by Caspase-1 in inflammasome complexes and has anti-obesity effects; however, it is not known which inflammasome regulates this process. We found that mice lacking ...the NLRP1 inflammasome phenocopy mice lacking IL-18, with spontaneous obesity due to intrinsic lipid accumulation. This is exacerbated when the mice are fed a high-fat diet (HFD) or a high-protein diet, but not when mice are fed a HFD with low energy density (high fiber). Furthermore, mice with an activating mutation in NLRP1, and hence increased IL-18, have decreased adiposity and are resistant to diet-induced metabolic dysfunction. Feeding these mice a HFD further increased plasma IL-18 concentrations and strikingly resulted in loss of adipose tissue mass and fatal cachexia, which could be prevented by genetic deletion of IL-18. Thus, NLRP1 is an innate immune sensor that functions in the context of metabolic stress to produce IL-18, preventing obesity and metabolic syndrome.
Display omitted
•Deletion of NLRP1 in mice leads to obesity and metabolic syndrome•NLRP1 obesity phenotype is related to the energy quotient of the diet•Loss of NLRP1 decreased IL-18 production and lipolysis•NLRP1 activation increased IL-18, prevented obesity, but was fatal on the high-fat diet
Murphy et al. link the NLRP1 inflammasome to IL-18 production and show that mice lacking NLRP1 have defective lipolysis and become obese, as seen with IL-18 deficiency. NLRP1 activation prevents obesity but results in fatal fat loss and cachexia on a high-fat diet, which is rescued by deletion of IL-18.
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