Combined long and short timescale X-ray variability of NGC 4051 with RXTE and XMM-Newton

By I. McHardy, I. Papadakis, P. Uttley, K. Mason, M. M. U. O. Southampton, U. Crete, Mssl. 2003

292 citations recorded by the source corpus.

Abstract We present a comprehensive examination of the X-ray variability of the narrow line Seyfert 1 (NLS1) galaxy NGC 4051. We combine over 6.5 years of frequent monitoring observations by RXTE with a >100 ks continuous observation by XMM-Newton and so present a powerspectral density (PSD) covering an unprecedent frequency range of over 6.5 decades from 10−2 Hz. The combined RXTE and XMM-Newton PSD is a very good match to the PSD of the galactic black hole binary system (GBH) Cyg X-1 when in a ‘high’, rather than ‘low’, state providing the first definite confirmation of an AGN in a ‘high’ state. We find a break in the PSD at a frequency νB=8+4−3×10−4 Hz. If νB scales linearly with mass then, assuming a black hole (BH) mass of 10 M ⊙ for Cyg X-1, we imply a BH mass of 3+2−1×105 M⊙ in NGC 4051, which is consistent with the recently reported reverberation value of 5+6−3×105 M⊙. Hence NGC 4051 is emitting at ∼ 30% LEdd. We note that the higher energy photons lag the lower energy ones and that the lag is greater for variations of longer Fourier period and increases with the energy separation of the bands. Variations in different wavebands are very coherent at long Fourier periods but the coherence decreases at shorter periods and as the energy separation between bands increases. This behaviour is similar to that of GBHs and suggests a radial distribution of frequencies and photon energies with higher energies and higher frequencies being associated with smaller radii. It is not possible to fit all AGN to the same linear scaling of break timescale with black hole mass. Broad line AGN are consistent with a linear scaling of break timescale with mass from Cyg X-1 in its low state but NLS1 galaxies scale better with Cyg X-1 in its high state. We suggest that the relationship between black hole mass and break timescale is a function of another underlying parameter which may be accretion rate.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/c079c29c05c9774da3ad36f3cadbd49b27125ee6

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Citations in the corpus

Correlated Multi-Wave Band Variability in the Blazar 3C 279 from 1996 to 2007 (2008, background): “More recent studies indicate that some Seyfert galaxies have X-ray PSDs that are fit better by a broken power law, with a steeper slope above the break frequency (Uttley et al. 2002;McHardy et al. 2004;Markowitz et al. 2003; Edelson &Nandra 1999; Pounds et al. 2001).”
Generating artificial light curves: revisited and updated (2013, background): “Note that the derived best-fitting values agree entirely with the ones given by Vaughan et al. (2011) but that the best-fit fbend differs from the value 8+4−3 × 10−4 Hz estimated by McHardy et al. (2004) (note that the error estimates correspond to the 90 per cent confidence intervals).”
Broad iron L line and X-ray reverberation in 1H0707-495 (2009, background): “The break in the PSD in this propagation model may be related to the time-scale of the fluctuations at the outer radius of the X-ray emitting region (Kotov et al. 2001; McHardy et al. 2004).”
X-ray variability of 104 active galactic nuclei - XMM-Newton power-spectrum density profiles (2012, background): “…not clearly understood (Körding et al., 2006; Fender et al., 2006) but there is someevidence to support the idea that luminous, radio-quiet AGN represent supermassive analogues of BH-XRB in the ‘soft states’ (Uttley et al., 2002; McHardy et al., 2004; Uttley & McHardy, 2005; Vaughan et al., 2011).”
Investigating a fluctuating-accretion model for the spectral-timing properties of accreting black hole systems (2005, methodology): “…at, for example, the PSD bend frequency in each case gives a mass-independent measure, so an extrapolation of the lag spectra in NGC 4051 published by McHardy et al. (2004) down to the break time-scale would suggest that the lags in this case are indeed systematically larger than in MCG–6-30-15.”
A Bayesian test for periodic signals in red noise (2009, unknown): “The second model (H1) is a bending power law as advocated by McHardy et al. (2004) S(f) = βf−1 1 + f δ ffα−1 !”
Non‐linear X‐ray variability in X‐ray binaries and active galaxies (2005, background): “Principally, such models try to explain the shape of the power-spectral density function (PSD), which as a first approximation can be treated as a broken or more gently bending power-law (Belloni & Hasinger 1990; Nowak et al. 1999; McHardy et al. 2004)†.”
The Compact, Conical, Accretion-Disk Warm Absorber of the Seyfert 1 Galaxy NGC 4051 and Its Implications for IGM-Galaxy Feedback Processes (2007, background): “NGC 4051 is a low luminosity (Lbol = 2.5 × 1043 ergs s−1, Ogle et al. 2004), low black hole mass (MBH = 1.9 × 106 M⊙, Peterson et al. 2004) AGN, which varies rapidly (∼ 1 hour) and with large amplitude (a factor ∼10; McHardy et al. 2004).”
The subarcsecond mid-infrared view of local active galactic nuclei – II. The mid-infrared–X-ray correlation (2015, background): “Note that 0.3 dex also corresponds to the typical long-term variability found in individual AGN (e.g., McHardy et al. 2004).”
Rapid optical and X-ray timing observations of GX 339-4: multi-component optical variability in the low/hard state (2010, methodology): “We also tried different models, including an exponential cut-off powerlaw, as well as the bending power-law of McHardy et al. (2004), for the PSD fall-off above a Fourier frequency of∼1 Hz.”
MCG–6-30-15: long time-scale X-ray variability, black hole mass and active galactic nuclei high states (2005, methodology): “It is now reasonably well established that the X-ray powerspectral densities (PSDs) of AGN are broadly similar to those of galactic black hole X-ray binary systems (GBHs) (McHardy 1988; Edelson & Nandra 1999; Uttley et al. 2002; Markowitz et al. 2003; McHardy et al. 2004).”
X-ray reverberation around accreting black holes (2014, background): “The first time-scale dependent hard lags at low frequencies were discovered by Papadakis et al. (2001), with similar lags found in several other AGN (Vaughan et al. 2003b; McHardy et al. 2004; Arévalo et al. 2006; Markowitz et al. 2007; Arévalo et al. 2008a).”