Characterizing activity in AGN with Xray variability

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Characterizing activity in AGNwith X-ray
variability

• Rick Edelson

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Snippets of history

• Optical discovery study came first
• Seyfert classification based on emission lines
• First observations only possible in optical
• Still most accessible, well-studied waveband
• Flat IR thru X-ray SEDs, e.g. Elvis (1987)
• Mushotzky (2004, astro/ph0405144) review
• Concl most effective AGN surveys in X-rays
• Essentially all Radiating Supermassive Black
  Holes (AGN) show detectable hard X-ray activity

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X-rays are best activity indicator

• 1) Reach deepest into heart of the AGN
• Rapid var ? emission from inner lt-hrs
• Natural probe of central engine
• 2) No confusing emission components
• Other local components and external sources
  generally dont emit strongly in X-rays
• Other ls provide info on orientation, etc.
• Produced lt-days to lt-years out

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Principal Component Analysis

• PCA first applied to AGN by Boroson Green
  (1992, ApJS, 80,109)
• Optical data on 92 opt/UV-selected quasars
• Principal Eigenvector strong correlation of Hb
  width and Fe II strength, other line params
• Secondary strongly correlated with luminosity
• Principal eigenvector linked to X-ray slope
• Boller, Brandt Fink (1996, AA, 305, 53)
• X-ray softness correlated with Hb width

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Boller et al. (1996) correlation of Hb FWHM and
X-ray G
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X-ray variability in Radiating Supermassive Black
Holes

• Non-statistical indications of extreme
  variability in X-ray soft sources
• IRS 13224 Boller et al. (1997, MN, 289, 393)
• Akn 564 Edelson et al. (2002, ApJ, 568, 610)
• Statistical link w/X-ray var. amplitude (sxs)
• Turner et al. (1999, ApJ, 524, 667) andONeill
  et al. (2005, MNRAS, 358, 1405)
• Correlated excess variance w/ various
  properties for day-long ASCA light curves
• Found corr. w/ luminosity, optical params.

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35 days of X-ray coverage of Akn 564. Note
strong X-ray variability UV/optical varied 15
peak-peak in this period.
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Sixteen single-orbit light curves (1 point on
previous graph) in which Akn 564 varies by factor
of 2 within 3000 sec.
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Why X-ray Varibility Classification?

• AGN stick out the most in the X-rays
• X-rays give best access to nuclear region
• Bulk of lower-energy from lt-weeksyears out
• Optical emission lines formed lt-days out
• X-rays come from inner lt-hours
• Variability indicates activity time/size scale
• Test this by correlating X-ray variability with
  traditional eigenvectors of activity

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XMM and X-ray variability

• Rapid X-ray variability is a powerful tracer of
  activity in Radiating SMBHs
• XMM provides best opportunity to exploit it
• LEO light curves (ASCA, Swift) are interrupted
  this destroys key info on 3-10 ks timescale
• XMM can detect var. on lt100 sec timescales
• Chandra also uninterrupted, but lower sens.
• Sensitive, uninterrupted XMM light curves ideal
  probes of critical short timescales

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XMM Variability Study

• w/ Simon Vaughan, Ken Pounds
• XMM Variability Sample
• 29 Sy1s w/ gt30 ks obs, good bkgd, opt. data
• Measured Excess Variance (sxs)
• Measured 4 ks time scale shortest ever
• Errors on individual estimate of order unity
• Averaged multiple (10-100) estimates to beat down
  errors
• Confirmed that sxs stable in different periods

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XMM light curves of sources w/ a range of
variability levels. Note the tabulated quantity
is Fvar sqrt(sxs2).
Fvar 41
Fvar 22
Fvar lt 1.7
Fvar lt 1.7
Fvar 19
Fvar 11
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Variability Study Results

• Used ASURV to correlate 4 parameters
• X-ray excess variance (sxs)
• X-ray slope (G)
• Hb FWHM
• Luminosity (0.2-10 keV)
• Strongest correlations involved Hb
• sxs vs. Hb FWHM (p lt 0.01)
• G vs. Hb FWHM (p 0.26)
• sxs vs. Lx weaker than expected (p 1.6)

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Multi-parameter correlations. The strongest
correlations are shown on the left.
p lt 0.01
p 1.6
p 0.52
p 0.26
p 22
p 6.7
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Implications

• Short time scale X-ray variability better
  correlated w/ Hb FWHM than luminosity
• X-ray variability most likely linked to mass of
  supermassive black hole
• ? Hb FWHM is a better mass indicator than
  luminosity
• ? Efficiency is not constant
• Improved X-ray, optical data censored PCA
  methods key to further progress

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State of X-ray Astronomy

• Right now lots of X-ray satellites XMM, Chandra,
  RXTE, Suzuki Swift
• Con-X, XEUS mega-missions planned for the 2020s
• Doubtful they will proceed fully as hoped
• No missions are planned for the interim
• We will lose the ability to see in the X-rays
  starting in about 10 years
• This would be a disaster for AGN studies

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Conclusions

• Rapid X-ray variability most strongly correlated
  with Hb FWHM (an indicator of SMBH mass)
• X-rays are allowing the deepest probes of the
  central environment
• Access to the X-rays will be lost in next 10
  years unless we act quickly