X-ray variability of 104 active galactic nuclei XMM-Newton
power-spectrum density profiles
Authors: O.Gonzalez-Martin, S. Vaughan Speaker: Xuechen Zheng
2014.5.13
Introduction
1、 PSD: BH-XRB vs. AGN Similarities: power law, bend frequency BH-XRB: ‘state’– PSD shape QPOs problem
2、Main purpose: AGN PSD properties
Sample and Data
From XMM-Newton public archives until Feb. 2009: Z <0.4 Observation duration T >40 ksec Classification, redshift, mass, bolometric
luminosity: literature Sample: 209 observations and 104
distinct AGN(61 Type-1, 21 Type-2, 15 NLSy1, 7 BLLACs)
2 – 10 keV luminosity
2-10 kev luminosity fitting using absorbed power-law model Required only reasonable estimates LLAGN luminosity agree with other
literature Type- 1 Seyferts, QSOs, NLSy1: high
discrepancies soft-excess long-term variability
PSD estimation
For a given PSD model P(ν;θ), likelihood function:
I: observed P: model Confidence intervals:
/2
1
2 logN
jj
j j
IS P
P
min
1.0 68.3%S S S
Select model
LRT: Likelihood ratio test
Not well calibrated Accurate calibration: computation
expensive
2ln null
alternative
LD
L
QPOs check
1、 Largest outlier vs. Chi-squared distribution for periodogram Candidate: p<0.01
2、 Similar test to smoothing periodogram (top-hat filter) QPOs broader than frequency resolution
p-value not correctly calibrated, crude but efficient
Result 1 - variability
75 out of 104 AGN show variability No variability: 12 of 14 LINERs, 2 of
11 Type-2 Seyferts, 12 of 54 Type-1 Seyferts, 2 of 3 QSOs, 1 of 7 BLLACs
Result 2 -- Model selection
Low number of bins in the PSD above Poisson noise some sources unable to constrained parameters
Model B: 17 vs. Papadakis et al.(2010): bump or
QPOs? 16 Type-1, 1 S2
Result 3
QPOs: only one candidate Slope:
Model A ---- α=2.01±0.01(T) 2.06±0.01(S) 1.77±0.01(H)
K-S test distributions statistically indistinguishable
Model B ---- α=3.08±0.04(T) 3.03±0.01(S) 3.15±0.08(H)
Result 6 -- Leakage
Leakage bias: reduce sensitivity to bends and QPOs model A α ≈ 2: possibly be affected
‘End matching’(Fougere 1985) reduce leakage bias remove linear trend: first and last point
equal model A indices higher than before but
lower than high frequency index in bend PSDs
Result summary
1、 72% of the sample show variability, most LINERs do not vary
2、 17 sources (16 Type-1 Seyferts) model B; others model A
3、 slope discrepancy between model A and B
4、 only one QPO (hard to detect)
Scaling relation
Equation 1: A = 1.09 ±0.21 C = -1.70 ±0.29 SSE :11.14 for 19 dof
Equation 2: A = 1.34 ±0.36 B = -0.24 ±0.28 C = -1.88 ±0.36 SSE: 10.69 for 18 dof
Scaling relation
Cygnus X-1: test relation on BH-XRB vs. McHardy et al.(2006):
Weak dependence of T_b on L Use smaller mass dependence
recover( B = -0.70 ±0.30) Maybe due to uncertainties
BLR vs. variability
McHardy et al.(2006): correlation between T and optical line widths(V)
Lines: Hβ, Paβ Correlation coefficient: r = 0.692
D = 2.9 ±0.7 E = -10.2±2.3 SSE: 13.47 for 19 dof
PSD shapes
Model B high frequency slope steep: May be similar to BH-XRB‘soft’states XMM-Newton and RXTE Selection effect
Majority of sample show no bend: Massive object have lower v_b Leakage bias selection effect
Bends: M_bh, L expected T_b 17 source bends within
frequency range(13 detected)