J/A+A/473/105 Lockman Hole AGN variability with XMM (Mateos+, 2007)
XMM-Newton observations of the Lockman Hole.
V. Time variability of the brightest AGN.
Mateos S., Barcons X., Carrera F.J., Page M.J., Ceballos M.T., Hasinger G.,
Fabian A.C.
<Astron. Astrophys., 473, 105-120 (2007)>
=2007A&A...473..105M 2007A&A...473..105M
ADC_Keywords: X-ray sources ; Active gal. nuclei
Keywords: X-rays: general - galaxies: active
Abstract:
This paper presents the results of a study of X-ray spectral and flux
variability on time scales from months to years, of the 123 brightest
objects (including 46 type-1 AGN and 28 type-2 AGN) detected with
XMM-Newton in the Lockman Hole field. We detected flux variability
with a significance ≥3σ in ∼50% of the objects, including
68±11% and 48±15% among our samples of type-1 and type-2 AGN.
However we found that the fraction of sources with best quality light
curves that exhibit flux variability on the time scales sampled by our
data is ≥80%, i.e the great majority of the AGN population may
actually vary in flux on long time scales. The mean relative intrinsic
amplitude of flux variability was found to be ∼0.15 although with a
large dispersion in measured values, from ∼0.1 to ∼0.65. The flux
variability properties of our samples of AGN (fraction of variable
objects and amplitude of variability) do not significantly depend
on the redshift or X-ray luminosity of the objects and seem to be
similar for the two AGN types. Using a broad band X-ray colour we
found that the fraction of sources showing spectral variability
with a significance ≥3σ is ∼40% i.e. less common than flux
variability. Spectral variability was found to be more common in
type-2 AGN than in type-1 AGN with a significance of more than 99%.
This result is consistent with the fact that part of the soft
emission in type-2 AGN comes from scattered radiation, and this
component is expected to be much less variable than the hard
component. The observed flux and spectral variability properties of
our objects and especially the lack of correlation between flux and
spectral variability in most of them cannot be explained as being
produced by variability of one spectral component alone, for example
changes in Gamma associated with changes in the mass accretion rate,
or variability in the amount of X-ray absorption. At least two
spectral components must vary in order to explain the X-ray
variability of our objects.
Description:
The XMM-Newton observatory has carried out its deepest observation in
the direction of the Lockman Hole field, centred at RA=10:52:43 and
DE=+57:28:48 (J2000). The XMM-Newton deep survey in the Lockman Hole
is composed of 16 observations carried out from 2000 to 2002, which
allow us to study the X-ray variability properties of our sources on
long time scales, from months to years.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table4.dat 89 123 Summary of detection of X-ray variability in
Lockman Hole sources
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See also:
J/A+A/393/425 : Spectral analysis of Lockman Hole (Mainieri+, 2002)
J/A+A/444/79 : XMM observations of Lockman Hole brightest AGNs (Mateos+, 2005)
J/A+A/479/283 : XMM observations of the Lockman Hole (Brunner+, 2008)
Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1- 4 I4 --- [MBC2005] Source sequential number
6- 8 I3 --- RDS ? X-ray source ROSAT number (RDS NNN)
10- 13 A4 --- RDSO Optical source ROSAT number (RDS NNNA)
15- 16 I2 h RAh Right ascension (J2000.0) (1)
18- 19 I2 min RAm Right ascension (J2000.0) (1)
21- 25 F5.2 s RAs Right ascension (J2000.0) (1)
27 A1 --- DE- Declination sign (J2000.0) (1)
28- 29 I2 deg DEd Declination (J2000.0) (1)
31- 32 I2 arcmin DEm Declination (J2000.0) (1)
34- 38 F5.2 arcsec DEs Declination (J2000.0) (1)
40- 44 A5 --- --- [type- ]
45 I1 --- AGN [1,2]? AGN class from optical spectroscopy
47- 51 F5.3 --- z ? Redshift
53- 58 A6 --- Model Best fit spectral model (2)
60 A1 --- l_SFlux Limit on SFlux
61- 65 F5.2 % SFlux ?=- Significance of detection of
flux variability
67 A1 --- l_SSpec Limit on SSpec
68- 72 F5.2 % SSpec ?=- Significance of detection of
spectral variability
74 A1 --- l_sigma Limit on sigma
75- 78 F4.2 --- sigma ?=- Intrinsic amplitude of flux variability
80- 83 F4.2 --- e_sigma ? Low error bar of sigma
86- 89 F4.2 --- E_sigma ? High error bar of sigma
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Note (1): The coordinates of the sources RA and Dec, are not the X-ray
positions from the Lockman Hole catalogue (Brunner et al., 2008,
Cat. J/A+A/479/283), but the centres of the regions used to extract
the spectra of the objects.
Note (2): Model as follows:
SPL = Single power law
APL = Absorbed power law
SE = Soft excess emission
CAPL = Absorption with partial covering absorber
2SPL = Two power laws (to fit spectral hardening at high energies)
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Acknowledgements:
Silvia Mateos, sm279(at)star.le.ac.uk
References:
Hasinger et al., Paper I 2001A&A...365L..45H 2001A&A...365L..45H
Mainieri et al., Paper II 2002A&A...393..425M 2002A&A...393..425M, Cat. J/A+A/393/425
Streblyanska et al., Paper III 2005A&A...432..395S 2005A&A...432..395S
Mateos et al., Paper IV 2005A&A...444...79M 2005A&A...444...79M, Cat. J/A+A/444/79
(End) Patricia Vannier [CDS] 05-Mar-2008