X-ray variability of 104 active galactic nuclei

González‐Martín, O.; Vaughan, S.

doi:10.1051/0004-6361/201219008

Cited by 198 publications

(249 citation statements)

References 109 publications

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“…∼100 ks) allows us to estimate the PSD down to frequencies as low as ∼10 −5 Hz, which is approximately a factor of 2 lower than possible with previous archival data for this source (e.g. González-Martín & Vaughan 2012).…”

Section: The Power Spectrummentioning

confidence: 72%

“…The observed bend frequency for PG 1211+143 corresponds to a time-scale of T b = 1/ν b = 14 +6 −3 ks (or 0.16 +0.07 −0.03 days). González-Martín & Vaughan (2012) provide a simple scaling relation between the observed bend time-scale and black hole mass for AGN:…”

Section: The Power Spectrummentioning

confidence: 99%

“…Assuming a black hole mass for PG 1211+143 of MBH ∼ 10 7−8 M⊙ (Kaspi et al 2000;Peterson et al 2004) and values of A = 1.09 and C = −1.70, as derived by González-Martín & Vaughan (2012) from fitting equation 1 to a sample of known Seyferts, this predicts a bend time-scale in the range ν b ∼ 0.2-3 days. Given our observed value of ν b ∼ 0.16 days, this is more consistent with a lower black hole mass estimate (e.g.…”

Section: The Power Spectrummentioning

confidence: 99%

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X-ray timing analysis of the quasar PG 1211+143

Lobban

Vaughan

Pounds

et al. 2016

Mon. Not. R. Astron. Soc.

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We report on a timing analysis of a new ∼630 ks XMM-Newton observation of the quasar, PG 1211+143. We find a well-defined X-ray power spectrum with a well-detected bend at ∼7 ×10 −5 Hz, consistent with the established t bend -M BH correlation for luminous, accreting black holes. We find the linear rms-flux relation commonly observed in accreting black hole systems and investigate the energy-dependence of the rms. The fractional rms is roughly constant with energy on short timescales (< 1 day; within observations) whereas there is enhanced soft band variability on long timescales (between observations typically spaced by a few days). Additionally, we also report on the optical-UV variability using the OM on-board XMM-Newton and a ∼2-month-long overlapping monitoring programme with Swift. We find that, although there is little UV variability within observations (< 1 day), UV variations of a few per cent exist on time-scales of ∼days-weeks.

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Section: The Power Spectrummentioning

confidence: 72%

Section: The Power Spectrummentioning

confidence: 99%

Section: The Power Spectrummentioning

confidence: 99%

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X-ray timing analysis of the quasar PG 1211+143

Lobban

Vaughan

Pounds

et al. 2016

Mon. Not. R. Astron. Soc.

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“…By using this analysis, González-Martín & Vaughan (2012) found 14% of variable LINERs, compared with 79% found for Seyfert galaxies.…”

Section: Introductionmentioning

confidence: 93%

“…For a one-epoch observation, when high signal-to-noise data are available, short-timescale variations can be investigated through a power spectral density (PSD) analysis of the light curve (Lawrence et al 1987;González-Martín & Vaughan 2012). By using this analysis, González-Martín & Vaughan (2012) found 14% of variable LINERs, compared with 79% found for Seyfert galaxies.…”

Section: Introductionmentioning

confidence: 99%

X-ray spectral variability of LINERs selected from the Palomar sample

Hernández-García

González‐Martín

Masegosa

et al. 2014

A&A

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Context. Variability is a general property of active galactic nuclei (AGN). The way in which these changes occur at X-rays is not yet clearly understood. In the particular case of low-ionization nuclear emission line region (LINER) nuclei, variations on the timescales from months to years have been found for some objects, but the main driver of these changes is still debated. Aims. The main purpose of this work is to investigate the X-ray variability in LINERs, including the main driver of these variations, and to search for possible differences between type 1 and 2 objects. Methods. We examined the 18 LINERs in the Palomar sample with data retrieved from the Chandra and/or XMM-Newton archives that correspond to observations gathered at different epochs. All the spectra for the same object were fitted simultaneously to study long-term variations. The nature of the variability patterns were studied by allowing different parameters to vary during the spectral fit. Whenever possible, short-term variations from the analysis of the light curves and long-term UV variability were studied. Results. Short-term variations are not reported in X-rays. Three LINERs are classified as non-AGN candidates in X-rays, all of them are Compton-thick candidates; none of them show variations at these frequencies, and two of them vary in the UV. Long-term X-ray variations were analyzed in 12 out of 15 AGN candidates; about half of them showed variability (7 out of the 12). At UV frequencies, most of the AGN candidates with available data are variable (five out of six). Thus, 13 AGN candidates are analyzed at UV and/or X-rays, ten of which are variable at least in one energy band. None of the three objects that do not vary in X-rays have available UV data. This means that variability on long-timescales is very common in LINERs. These X-ray variations are mainly driven by changes in the nuclear power, while changes in absorptions are found only for NGC 1052. We do not find any difference between type 1 and 2 LINERs, neither in the number of variable cases (three out of five type 1 and four out of seven type 2 LINERs), nor in the nature of the variability pattern. We find indications of an anticorrelation between the slope of the power law, Γ, and the Eddington ratio. Conclusions. LINERs are definitely variable sources irrespective of whether they are classified as optical type 1 or 2. Their BH masses, accretion rates, and variability timescales place them in the same plane as more powerful AGN at X-rays. However, our results suggest that the accretion mechanism in LINERs may be different. UV variations of some type 2 LINERs were found, this could support the hypothesis of a torus that disappears at low luminosities.

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Quasi periodic oscilations in active galactic nuclei

Alston¹,

Fabian²,

Markeviciute³

et al. 2016

Astron Nachr

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Quasi-periodic oscillations (QPOs) are coherent peaks of variability power observed in the X-ray power spectra (PSDs) of stellar mass X-ray binaries (XRBs). A scale invariance of the accretion process implies they should be present in the active galactic nuclei. The first robust detection was a ∼ 1 h periodicity in the Seyfert galaxy RE J1034+396 from a ∼ 90 ks XMM-Newton observation; however, subsequent observations failed to detect the QPO in the 0.3-10.0 keV band. In this talk we present the recent detection of the ∼ 1 h periodicity in the 1.0-4.0 keV band of 4 further low-flux/spectrally-harder observations of RE J1034+396 (see Alston et al. 2014). We also present recent work on the discovery of a QPO in the Seyfert galaxy, MS 2254.9-3712, which again is only detected in energy bands associated with the primary power-law continuum emission (Alston et al. 2015). We conclude these features are most likely analogous to the high-frequency QPOs observed in XRBs. In both sources, we also see evidence for X-ray reverberation at the QPO frequency, where soft X-ray bands and Iron Kα emission lag the primary X-ray continuum. These time delays may provide another diagnostic for understanding the underlying QPO mechanism observed in accreting black holes.

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X-ray variability of 104 active galactic nuclei

Cited by 198 publications

References 109 publications

X-ray timing analysis of the quasar PG 1211+143

X-ray timing analysis of the quasar PG 1211+143

X-ray spectral variability of LINERs selected from the Palomar sample

Quasi periodic oscilations in active galactic nuclei

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