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Register a new userModeling time delays in the X-ray spectrum of the Seyfert galaxy MCG-6-30-15
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R. W. Goosmann
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We propose a reflection model of the time delays detected during an exceptionally bright, single flare in MCG-6-30-15. We consider a scenario in which the delays of the hard X-rays with respect to the soft X-rays are caused by the presence of the delayed reflection component. We employ a model of the flare, which is accompanied by reprocessed emission. We consider two geometries/thermal states of the reprocessing medium: a partially ionized accretion disk surface and a distribution of magnetically confined, cold blobs. The reprocessing by cold blobs predicts positive time delays and a saturation in the time delay -- energy relation, which is likely present in the data. The model requires a strong reflection component and relies on the apparent pivoting of the combined primary and reflected spectrum. The reflection by the ionized disk surface does not reproduce the observed delays. We discuss the relation between the two reflection scenarios and argue that they are both present in MCG-6-30-15.
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We discuss implications of a strong flare event observed in the Seyfert galaxy MCG-6-30-15 assuming that the emission is due to localized magnetic reconnection. We conduct detailed radiative transfer modeling of the reprocessed radiation for a primary source that is elevated above the disk. The model includes relativistic effects and Keplerian motion around the black hole. We show that for such a model setup the observed time-modulation must be intrinsic to the primary source. Using a simple analytical model we then investigate time delays between hard and soft X-rays during the flare. The model considers an intrinsic delay between primary and reprocessed radiation, which measures the geometrical distance of the flare source to the reprocessing sites. The observed time delays are well reproduced if one assumes that the reprocessing happens in magnetically confined, cold clouds.
We present a multiwaveband spectroscopic study of the nearby Seyfert 1 galaxy MCG-6-30-15. New optical spectra from the Anglo-Australian Telescope are presented which clearly show the effects of dust extinction/reddening on both the emission line spectrum and the non-stellar AGN continuum. The reddening is constrained to be in the range E(B-V)=0.61-1.09. Spectroscopy in the X-ray band, with both ROSAT and ASCA, reveal absorption by the warm absorber but little or no neutral absorption expected to accompany the dust responsible for the optical reddening. The dusty warm absorber solution to this discrepancy is discussed and photoionization models of such warm absorbers are constructed. The optical spectrum also displays the relatively strong `coronal lines of [FeX]6375, [FeXI]7892 and [FeXIV]5303. We show that these lines may plausibly originate from the outer regions of the warm absorber, although better calculations of the collision strengths for these transitions are required in order to conclusively address this issue. We also present new ultraviolet data from the International Ultraviolet Explorer and suggest that much of the observed UV flux is scattered into our line of sight (with a scattering fraction of 1-5 per cent). We conclude with a discussion of the global energetics of this system.
We report the first simultaneous measure of the X-ray broadband (0.1--200 keV) continuum and of the iron K-alpha fluorescent line profile in the Seyfert 1 galaxy MCG-6-30-15. Our data confirms the ASCA detection of a skewed and redshifted line profile (Tanaka et al. 1995). The most straightforward explanation is that the line photons are emitted in the innermost regions of a X-ray illuminated relativistic disk. The line Equivalent Width (~200 eV) is perfectly consistent with the expected value for solar abundances, given the observed amount of Compton reflection. We report also the discovery of a cut-off in the nuclear primary emission at the energy of ~160 keV.
The flux-flux plot (FFP) method can provide model-independent clues regarding the X-ray variability of active galactic nuclei. To use it properly, the bin size of the light curves should be as short as possible, provided the average counts in the light curve bins are larger than $sim 200$. We apply the FFP method to the 2013, simultaneous XMM-Newton and NuSTAR observations of the Seyfert galaxy MCG$-$6-30-15, in the 0.3-40 keV range. The FFPs above $sim 1.6$ keV are well-described by a straight line. This result rules out spectral slope variations and the hypothesis of absorption driven variability. Our results are fully consistent with a power-law component varying in normalization only, with a spectral slope of $sim 2$, plus a variable, relativistic reflection arising from the inner accretion disc around a rotating black hole. We also detect spectral components which remain constant over $sim 4.5$ days (at least). At energies above $sim 1.5$ keV, the stable component is consistent with reflection from distant, neutral material. The constant component at low energies is consistent with a blackbody spectrum of $kT_{rm BB} sim 100$ eV. The fluxes of these components are $sim 10-20%$ of the average continuum flux (in the respective bands). They should always be included in the models that are used to fit the spectrum of the source. The FFPs below 1.6 keV are non-linear, which could be due to the variable warm absorber in this source.
We used a ~300 ks long XMM-Newton observation of the Seyfert 1 galaxy MCG-6-30-15 to study the correlation between the 0.2-10 keV X-ray and the 3000-4000 A bands. We found a significant correlation peak at a time lag of 160 ks where the UV flux variations preceded the variations in the X-ray band. We interpret this result as evidence in favour of Comptonisation models where the observed X-rays are produced through Compton up-scattering of thermal UV seed photons from an accretion disc, as this process naturally predicts the UV variations to precede similar flux variations in the X-rays. The length of the time lag favours models where the observed UV and the seed-photon-emitting regions are connected by perturbations of the accretion flow traveling inwards through the disc, affecting first the main U-band-emitting radii and then the innermost region where the bulk of the seed photons is expected to be produced. Finally, the absence of significant features in the correlation function with X-ray flux variations preceding those in the UV indicates that the observed U-band photons are not mainly produced through reprocessing of hard X-rays in this source.
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