The long time-scale X-ray variability of the radio-quiet quasar PG 0804+761

Papadakis, I. E.; Reig, P.; Nandra, K.

doi:10.1046/j.1365-8711.2003.06891.x

Cited by 13 publications

(17 citation statements)

References 28 publications

(48 reference statements)

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“…PG 0804+761 (z = 0.100) PG 0804+761 was one of the brightest radio-quiet quasars observed by ASCA with a energy spectrum well represented by a simple power law model with a photon index of 2.18 +0.02 −0.03 in the 2-10 keV energy range with no significant Fe K emission detected (George et al 2000). Recently, Papadakis et al (2003) found similar results with RXTE analyzing the spectrum averaged over one year (Γ 3−15 keV = 2.10 +0.12 −0.10 and no Fe K line is statistically required). The flux variations appeared not to be associated with any spectral variations.…”

Section: Appendix A: Notes On Individual Objectsmentioning

confidence: 99%

XMM-Newton EPIC observations of 21 low-redshift PG quasars

Porquet

Reeves

O’Brien

et al. 2004

A&A

261

291

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Abstract. We present an X-ray spectral analysis of 21 low redshift quasars observed with XMM-Newton EPIC. All the sources are Palomar Green quasars with redshifts between 0.05 and 0.4 and have low Galactic absorption along the line-of-sight. A large majority of quasars in the sample (19/21) exhibit a significant soft excess below ∼1-1.5 keV, whilst two objects (PG 1114+445 and I Zw1) show a deficit of soft X-ray flux due to the presence of a strong warm absorber. Indeed, contrary to previous studies with ASCA and ROSAT, we find that the presence of absorption features near 0.6-1.0 keV is common in our sample. At least half of the objects appear to harbor a warm absorber, as found previously in Seyfert 1 galaxies. We find significant detections of Fe Kα emission lines in at least twelve objects, whilst there is evidence for some broadening of the line profile, compared to the EPIC-pn resolution, in five of these quasars. The determination of the nature of this broadening (e.g., Keplerian motion, a blend of lines, relativistic effects) is not possible with the present data and requires either higher S/N or higher resolution spectra. In seven objects the line is located between 6.7-7 keV, corresponding to highly ionized iron, whereas in the other five objects the line energy is consistent with 6.4 keV, i.e. corresponding to near neutral iron. The ionized lines tend to be found in the quasars with the steepest X-ray spectra. We also find a correlation between the continuum power law index Γ and the optical Hβ width, in both the soft and hard X-ray bands, whereby the steepest X-ray spectra are found in objects with narrow Hβ widths, which confirms previous ROSAT and ASCA results. The soft and hard band X-ray photon indices are also strongly correlated, i.e. the steepest soft X-ray spectra correspond the steepest hard X-ray spectra. We propose that a high accretion rate and a smaller black hole mass is likely to be the physical driver responsible for these trends, with the steep spectrum objects likely to have smaller black hole masses accreting near the Eddington rate.

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Section: Appendix A: Notes On Individual Objectsmentioning

confidence: 99%

XMM-Newton EPIC observations of 21 low-redshift PG quasars

Porquet

Reeves

O’Brien

et al. 2004

A&A

261

291

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“…We fitted both PSDs with a power-law model (PL) of the form: P( f ) = A(10 4 f ) −α + C, taking into account aliasing effects (as in Papadakis et al 2003). The constants A and C are the PL normalization (equal to the PSD value at 10 −4 Hz) and the Poisson noise level, respectively.…”

Section: The High Frequency Power Spectrummentioning

confidence: 99%

XMM-Newtonlong-look observation of the narrow-line Seyfert 1 galaxy PKS 0558–504

Papadakis¹,

Brinkmann²,

Gliozzi³

et al. 2010

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Context. PKS 0558-504 has been observed repeatedly by XMM-Newton as a calibration and performance verification target. In this work, we present results from the power spectral analysis using data from a long XMM-Newton observation and archival RXTE data. Aims. To search for periodic and/or quasi-periodic signals, to estimate the power spectrum over a broad range which covers almost six decades in frequency, and to compare the variability in the ultraviolet (UV), soft and hard X-ray bands. Methods. We used the XMM-pn soft and hard band light curves to compute the high frequency power spectrum (PSD) and search for periodicities. We also used an archival, long RXTE light curve to constrain the power spectrum at low frequencies, and the XMM-OM light curve to estimate the UV PSD. We also used the results from the time-resolved spectral studies we presented in a recent paper to compare in more detail the X-ray, "soft-excess" and UV variations. Results. We did not detect any significant periodic or quasi-periodic signals. The soft band power spectral slope is steeper than the hard band PSD slope, but consistent within the 1-σ uncertainties. The broad frequency band, 2−10 keV PSD follows a power-law like shape of an index ∼0.5 up to a break frequency at ∼7 × 10 −6 Hz (which corresponds to a time scale of 1.7 days). At higher frequencies, the PSD steepens to a slope of ∼2.2. The OM power spectrum has a significantly smaller amplitude than the X-ray and the soft-excess PSDs. Conclusions. The similarity between the PSD shape of PKS 0558-504 and other radio-quiet Seyferts 1 suggests a common variability (and emission) mechanism. Consequently any jet emission in the X-ray band should be unimportant in this source. Using the scaling relations between PSD break time scales and black hole mass/bolometric luminosity, we estimated a black hole mass of ∼2 × 10 8 M . Power spectral analysis of the light curves which resulted from the time-resolved spectroscopic study of the same data set indicates that the intrinsic power spectrum may steepen with increasing energy, contrary to what is currently believed for typical Seyferts. When scaled appropriately, the OM and soft-excess light curves show similar variability patterns. They may originate from the accretion disc, at a distance of ∼20 and 5 Schwarzschild radii, respectively, and their variations could be due to accretion rate variations, which operate on the local viscosity time scale and propagate inwards.

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“…Markowitz & Edelson (2001) have calculated the excess variance for nine Seyfert galaxies using 300‐d‐long, RXTE Proportional Counter Array (PCA), 2–10 keV light curves with a uniform 5‐d sampling. Recently, Papadakis et al (2003) calculated the excess variance of PG 0804+761 using a 1‐yr‐long, RXTE (PCA), 2–10 keV light curve with a 3‐d sampling. The sampling and duration of the quasar light curve are similar to the respective properties of the Seyfert galaxy light curves of Markowitz & Edelson.…”

Section: The Dependence Of Long‐term Variability Amplitude On Mbhmentioning

confidence: 99%

“…Note that NGC 5506 was recently classified as NLS1 (Nagar et al 2002). All σ 2 rms estimates in column (3) are taken from Markowitz & Edelson (2001), except from PG 0804+761 which is taken from Papadakis et al (2003). The numbers in parenthesis in column (4) correspond to the references for ν hfb as follows: (1) Markowitz et al (2003), (2) Uttley et al (2002), (3) Vaughan, Fabian & Nandra (2003), (4) Vaughan et al (2003), (5) McHardy et al (2003), (6) Shih, Iwasawa & Fabian (2003), (7) Papadakis et al (2002).…”

Section: The Dependence Of Long‐term Variability Amplitude On Mbhmentioning

confidence: 99%

“…The primary goal of the present work is to investigate the relation between excess variance and M bh using the σ 2 rms data of Markowitz & Edelson (2001), together with the recent σ 2 rms measurement of a radio‐quiet quasar, namely PG 0804+761 (Papadakis, Reig & Nandra 2003). Markowitz & Edelson (2001) have already shown that σ 2 rms is strongly anticorrelated with the source luminosity.…”

Section: Introductionmentioning

confidence: 99%

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The scaling of the X-ray variability with black hole mass in active galactic nuclei

Papadakis

2004

Monthly Notices of the Royal Astronomical Society

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172

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The relation between the 2–10 keV, long‐term, excess variance and active galactic nuclei (AGN) black hole mass is considered in this work. A significant anticorrelation is found between these two quantities in the sense that the excess variance decreases with increasing black hole mass. This anticorrelation is consistent with the hypothesis that the 2–10 keV power spectrum in AGN follows a power law of slope −2 at high frequencies. It then flattens to a slope of −1 below a break frequency, νhfb, until a second break frequency, νlfb, below which it flattens to a slope of 0. The ratio νhfb/νlfb is equal to 10–30, similar to the ratio of the respective frequencies in Cyg X‐1. The power spectrum amplitude in the (frequency × power) space does not depend on black hole mass. Instead, it is roughly equal to 0.02 in all objects. The high‐frequency break decreases with increasing black hole mass according to the relation νhfb= 1.5 × 10−6/(M/107 M⊙) Hz, in the case of ‘classical’ Seyfert 1 galaxies. The excess variance of NGC 4051, a narrow‐line Seyfert 1 object, is larger than is expected for its black hole mass and X‐ray luminosity. This can be explained if its νhfb is 20 times larger than the value expected in the case of a ‘classical’ Seyfert 1 with the same black hole mass. Finally, the excess variance versus X‐ray luminosity correlation is a by‐product of the excess variance versus black hole mass correlation, with AGN accreting at ∼ 0.1–0.15 times the Eddington limit. These results are consistent with recent results from the power spectral analysis of AGN. However, as they are based on data from a few objects only, further investigation is necessary to confirm that there is indeed a ‘universal’ power spectrum shape in AGN (in the sense that the value of the power spectrum parameters of most AGN will be distributed around the ‘canonical’ slope, and amplitude values listed above). One way to achieve this is to determine the excess variance versus black hole relation more accurately, using data from many more objects. This will be possible in the near future, because it is easier to measure the excess variance of archival light curves than to estimate their power spectrum. The excess variance versus black hole relation can therefore play an important role in the study of the X‐ray variability scaling with black hole mass in AGN.

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The long time-scale X-ray variability of the radio-quiet quasar PG 0804+761

Cited by 13 publications

References 28 publications

XMM-Newton EPIC observations of 21 low-redshift PG quasars

XMM-Newton EPIC observations of 21 low-redshift PG quasars

XMM-Newtonlong-look observation of the narrow-line Seyfert 1 galaxy PKS 0558–504

The scaling of the X-ray variability with black hole mass in active galactic nuclei

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