Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userThe nature of X-ray spectral variability in MCG-6-30-15
138
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
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.
rate research
Read More
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.
The bright Seyfert 1 galaxy mcg shows large variability on a variety of time scales. We study the $aproxlt 3$ day time scale variability using a set of simultaneous archival observations that were obtained from rxte and the {it Advanced Satellite for Cosmology and Astrophysics} (asca). The rxte observations span nearly $10^6$ sec and indicate that the X-ray Fourier Power Spectral Density has an rms variability of 16%, is flat from approximately 10^{-6} - 10^{-5} Hz, and then steepens into a power law $propto f^{-alpha}$ with $alphaaproxgt 1$. A further steepening to $alpha approx 2$ occurs between 10^{-4}-10^{-3} Hz. The shape and rms amplitude are comparable to what has been observed in gc and cyg, albeit with break frequencies that differ by a factor of 10^{-2} and 10^{4}, respectively. If the break frequencies are indicative of the central black hole mass, then this mass may be as low as $10^6 {rm M}_odot$. An upper limit of $sim 2$ ks for the relative lag between the 0.5-2 keV asca band compared to the 8-15 keV rxte band was also found. Again by analogy with gc and cyg, this limit is consistent with a relatively low central black hole mass.
MCG-6-30-15, at a distance of 37 Mpc (z=0.008), is the archetypical Seyfert 1 galaxy showing very broad Fe K$alpha$ emission. We present results from a joint NuSTAR and XMM-Newton observational campaign that, for the first time, allows a sensitive, time-resolved spectral analysis from 0.35 keV up to 80 keV. The strong variability of the source is best explained in terms of intrinsic X-ray flux variations and in the context of the light bending model: the primary, variable emission is reprocessed by the accretion disk, which produces secondary, less variable, reflected emission. The broad Fe K$alpha$ profile is, as usual for this source, well explained by relativistic effects occurring in the innermost regions of the accretion disk around a rapidly rotating black hole. We also discuss the alternative model in which the broadening of the Fe K$alpha$ is due to the complex nature of the circumnuclear absorbing structure. Even if this model cannot be ruled out, it is disfavored on statistical grounds. We also detected an occultation event likely caused by BLR clouds crossing the line of sight.
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.
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.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
