X-ray variability time scales in active galactic nuclei

Ishibashi, W.; Courvoisier, T. J. L.

doi:10.1051/0004-6361/200911958

Cited by 17 publications

(13 citation statements)

References 19 publications

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“…Alternatively, determining how the absorber responds to changes in the ionizing flux can provide reliable estimates of n H . Time-variability of the continuum is a known feature of AGN (e.g., Uttley et al 2003;McHardy et al 2006;Ishibashi & Courvoisier 2009). How the fractional population of each ion in the outflowing gas changes in response to variation in the ionizing continuum depends on the electron number density n e , which is 1.2n H in highly ionized gas.…”

Section: Introductionmentioning

confidence: 99%

Multiwavelength campaign on Mrk 509

Arav

Edmonds

Borguet

et al. 2012

A&A

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Aims. Active galactic nuclei (AGN) often show evidence of photoionized outflows. A major uncertainty in models for these outflows is the distance (R) to the gas from the central black hole. In this paper we use the HST/COS data from a massive multi-wavelength monitoring campaign on the bright Seyfert I galaxy Mrk 509, in combination with archival HST/STIS data, to constrain the location of the various kinematic components of the outflow. Methods. We compare the expected response of the photoionized gas to changes in ionizing flux with the changes measured in the data using the following steps: 1) We compare the column densities of each kinematic component measured in the 2001 STIS data with those measured in the 2009 COS data; 2) We use time-dependent photionization calculations with a set of simulated lightcurves to put statistical upper limits on the hydrogen number density (n H ) that are consistent with the observed small changes in the ionic column densities; 3) From the upper limit on n H , we calculate a lower limit on the distance to the absorber from the central source via the prior determination of the ionization parameter. Our method offers two improvements on traditional timescale analysis. First, we account for the physical behavior of AGN lightcurves. Second, our analysis accounts for the quality of measurement in cases where no changes are observed in the absorption troughs. Results. The very small variations in trough ionic column densities (mostly consistent with no change) between the 2001 and 2009 epochs allow us to put statistical lower limits on R between 100-200 pc for all the major UV absorption components at a confidence level of 99%. These results are mainly consistent with the independent distance estimates derived for the warm absorbers from the simultaneous X-ray spectra. Based on the 100-200 pc lower limit for all the UV components, this absorber cannot be connected with an accretion disc wind. The outflow might have originated from the disc, but based on simple ballistic kinematics, such an event had to occur at least 300 000 years ago in the rest frame of the source.

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Section: Introductionmentioning

confidence: 99%

Multiwavelength campaign on Mrk 509

Arav

Edmonds

Borguet

et al. 2012

A&A

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“…We have previously associated the PSD break timescale with the heating/cooling time of the electrons in the optically thin shocks within the clumpy accretion scenario (Ishibashi & Courvoisier 2009b). Here we suggest that the X-ray PSD break timescale could be associated with the cooling time of electrons in the Comptonisation process, independently of the details of any specific accretion model.…”

Section: Discussionmentioning

confidence: 99%

“…In this picture, the break timescale is associated with a characteristic timescale, usually the viscous time, at the truncation radius of the standard accretion disc. In an alternative approach, we have discussed the characteristic X-ray variability timescale within the framework of a clumpy accretion model in AGN (Ishibashi & Courvoisier 2009b). In this scenario, accretion onto the central black hole occurs through a sequence or cascade of shocks, which are at the origin of the observed radiation.…”

Section: Introductionmentioning

confidence: 99%

The physical origin of the X-ray power spectral density break timescale in accreting black holes

Ishibashi¹,

Courvoisier²

2012

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X-ray variability of active galactic nuclei (AGN) and black hole binaries can be analysed by means of the power spectral density (PSD). The break observed in the power spectrum defines a characteristic variability timescale of the accreting system. The empirical variability scaling that relates characteristic timescale, black hole mass, and accretion rate (T B ∝ M 2.1 BH /Ṁ 0.98 ) extends from supermassive black holes in AGN down to stellar-mass black holes in binary systems. We suggest that the PSD break timescale is associated with the cooling timescale of electrons in the Comptonisation process at the origin of the observed hard X-ray emission. We find that the Compton cooling timescale directly leads to the observational scaling and naturally reproduces the functional dependence on black hole mass and accretion rate (t C ∝ M 2 BH /Ṁ). This result simply arises from general properties of the emission mechanism and is independent of the details of any specific accretion model.

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“…We derive a characteristic time scale, τ X , associated with the heating/cooling process of the electrons responsible for the X-ray emission [3].…”

Section: X-ray Variability Time Scalementioning

confidence: 99%