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Register a new userThe Energy-dependent X-ray Timing Characteristics of the Narrow Line Seyfert 1 Mkn 766
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A. Markowitz
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We present the energy-dependent power spectral density (PSD) and cross-spectral properties of Mkn 766, obtained from combining data obtained during an XMM-Newton observation spanning six revolutions in 2005 with data obtained from an XMM-Newton long-look in 2001. The PSD shapes and rms-flux relations are found to be consistent between the 2001 and 2005 observations, suggesting the 2005 observation is simply a low-flux extension of the 2001 observation and permitting us to combine the two data sets. The resulting PSD has the highest temporal frequency resolution for any AGN PSD measured to date. Applying a broken power-law model yields break frequencies which increase in temporal frequency with photon energy. Obtaining a good fit when assuming energy-independent break frequencies requires the presence of a Lorentzian at 4.6+/-0.4 * 10^-4 Hz whose strength increases with photon energy, a behavior seen in black hole X-ray binaries. The cross-spectral properties are measured; temporal frequency-dependent soft-to-hard time lags are detected in this object for the first time. Cross-spectral results are consistent with those for other accreting black hole systems. The results are discussed in the context of several variability models, including those based on inwardly-propagating viscosity variations in the accretion disk.
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We compute Fourier-resolved X-ray spectra of the Seyfert 1 Markarian 766 to study the shape of the variable components contributing to the 0.3-10 keV energy spectrum and their time-scale dependence. The fractional variability spectra peak at 1-3 keV, as in other Seyfert 1 galaxies, consistent with either a constant contribution from a soft excess component below 1 keV and Compton reflection component above 2 keV, or variable warm absorption enhancing the variability in the 1-3 keV range. The rms spectra, which shows the shape of the variable components only, is well described by a single power law with an absorption feature around 0.7 keV, which gives it an apparent soft excess. This spectral shape can be produced by a power law varying in normalisation, affected by an approximately constant (within each orbit) warm absorber, with parameters similar to those found by Turner et al. for the warm-absorber layer covering all spectral components in their scattering scenario. The total soft excess in the average spectrum can therefore be produced by a combination of constant warm absorption on the power law plus an additional less variable component. On shorter time-scales, the rms spectrum hardens and this evolution is well described by a change in power law slope, while the absorption parameters remain the same. The frequency dependence of the rms spectra can be interpreted as variability arising from propagating fluctuations through an extended emitting region, whose emitted spectrum is a power law that hardens towards the centre. This scenario reduces the short time-scale variability of lower energy bands making the variable spectrum harder on shorter time-scales and at the same time explains the hard lags found in these data by Markowitz et al.
We have analyzed the timing properties of the Narrow-line Seyfert 1 galaxy Mrk 766 observed with XMM-Newton during the PV phase. The source intensity changes by a factor of 1.3 over the 29,000 second observation. If the soft excess is modeled by a black body component, as indicated by the EPIC pn data, the luminosity of the black body component scales with its temperature according to L ~ T^4. This requires a lower limit black body size` of about 1.3*10^25 cm^2. In addition, we report the detection of a strong periodic signal with 2.4*10^-4 Hz. Simulations of light curves with the observed time sequence and phase randomized for a red noise spectrum clearly indicate that the periodicity peak is intrinsic to the distant AGN. Furthermore, its existence is confirmed by the EPIC MOS and RGS data. The spectral fitting results show that the black body temperature and the absorption by neutral hydrogen remain constant during the periodic oscillations. This observational fact tends to rule out models in which the intensity changes are due to hot spots orbiting the central black hole. Precession according to the Bardeen-Petterson effect or instabilities in the inner accretion disk may provide explanations for the periodic signal.
We present the results of our study of the long term X-ray variability characteristics of the Narrow Line Seyfert 1 galaxy RE J1034+396. We use data obtained from the AstroSat satellite along with the light curves obtained from XMM-Newton and Swift-XRT. We use the 0.3 - 7.0 keV and 3 - 20 keV data, respectively, from the SXT and the LAXPC of AstroSat. The X-ray spectra in the 0.3 - 20 keV region are well fit with a model consisting of a power-law and a soft excess described by a thermal-Compton emission with a large optical depth, consistent with the earlier reported results. We have examined the X-ray light curves in the soft and hard X-ray bands of SXT and LAXPC, respectively, and find that the variability is slightly larger in the hard band. To investigate the variability characteristics of this source at different time scales, we have used X-ray light curves obtained from XMM-Newton data (200 s to 100 ks range) and Swift-XRT data (1 day to 100 day range) and find that there are evidences to suggest that the variability sharply increases at longer time scales. We argue that the mass of the black hole in RE J1034+396 is likely to be $sim$3 $times$ 10$^6$ M$_odot$, based on the similarity of the observed QPO to the high frequency QPO seen in the Galactic black hole binary, GRS 1915+105.
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We present a power spectral analysis of a 100 ksec XMM-Newton observation of the narrow line Seyfert 1 galaxy Ark~564. When combined with earlier RXTE and ASCA observations, these data produce a power spectrum covering seven decades of frequency which is well described by a power law with two very clear breaks. This shape is unlike the power spectra of almost all other AGN observed so far, which have only one detected break, and resemble Galactic binary systems in a soft state. The power spectrum can also be well described by the sum of two Lorentzian-shaped components, the one at higher frequencies having a hard spectrum, similar to those seen in Galactic binary systems. Previously we have demonstrated that the lag of the hard band variations relative to the soft band in Ark 564 is dependent on variability time-scale, as seen in Galactic binary sources. Here we show that the time-scale dependence of the lags can be described well using the same two-Lorentzian model which describes the power spectrum, assuming that each Lorentzian component has a distinct time lag. Thus all X-ray timing evidence points strongly to two discrete, localised, regions as the origin of most of the variability. Similar behaviour is seen in Galactic X-ray binary systems in most states other than the soft state, i.e. in the low-hard and intermediate/very high states. Given the very high accretion rate of Ark 564 the closest analogy is with the very high (intermediate) state rather than the low-hard state. We therefore strengthen the comparison between AGN and Galactic binary sources beyond previous studies by extending it to the previously poorly studied very high accretion rate regime.
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