Invertedspectrum active galactic nuclei

1
Inverted-spectrum active galactic nuclei

• Ilona Jussila
• Metsähovi Radio Observatory

2
Normal AGNs

• Continuum spectra falling at radio frequencies
• Size Mpc

3
Inverted-spectrum sources

• Gigahertz-peaked spectrum (GPS) sources
• Turnover 1 GHz
• Size 1kpc
• even 10 of all AGN (ODea, 1998)
• very little variability

• Compact steep-spectrum (CSS) sources
• Turnover 100 MHz
• Size lt 15 kpc
• 15 - 30 of all AGN (Fanti et al., 1990)

4
Unification of inverted-spectrum AGN

• CSS and GPS sources related?
• Small size and spectral shape should be explained
• Youth scenario (Mutel and Phillips, 1988)
• Frustration scenario (Gopal-Krishna and Wiita,
  1991)
• Recurrent activity (Baum et al. 1990)

5
High-peaking GPS sources

• High-peaking GPS sources
• Peak frequency gt10GHz, even up to 100GHz during
  bursts
• Variable!? (Tornikoski et al., 2001, Jussila
  2002)
• Important for Planck Surveyor

6
The study

• Original goal
• to identify new high-peaking GPS sources
• to study the variability of the known ones
• Sample
• Successful observations for 41 sources
• 13 new candidates
• 28 known inverted-spectrum sources
• Morphologically quasars, BL Lacs and radio
  galaxies
• Monitored in Metsähovi since autumn 2001_at_37 GHz
• Some observations at SEST in Chile
• Additional data from literature

7
The results so far...

• New candidates
• 7 / 13 sources turned out to be flat spectrum
  sources with inverted spectrum during the bursts
  (IDB)
• 6 / 13 were inverted but very variable
• No classical high-peaking GPS sources found!

8
The results so far...

• Known GPS sources
• Half of the bona fide GPS sources turned out to
  be flat-spectrum sources with inverted spectrum
  during the bursts (IDB)
• gt The classification has been done with too
  sparse data

9
The results so far...

• Known GPS sources
• Many of the remaining genuine GPS sources
  exhibited variability ?Original definition!
• gt The classification of the sources has been
  done with too sparse data!
• gt The concept of GPS sources should be
  re-examined

10
The results so far

• Most of the rest genuine GPS sources had so
  sparse data that the interpretation is not
  reliable
• gt more data needed to reveal the multi-epoch
  spectra
• It is possible that of all GPS sources a
  considerable proportion will lose their
  GPS-classification

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Questions

• How many of the GPS sources are variable? Really
  inverted during the quiescent phases? High
  peaking?
• Is there evidence for a totally new group IDB
  (Inverted During Bursts) sources with flat
  quiescent spectrum and very inverted flare
  spectrum?

12
The Future

• Monitoring continues at Metsähovi
• gt Multi-epoch data on high frequency variability
  of the sources
• gt The sample extended to include also
  galaxy-type GPS sources will they exhibit
  variability too?
• Observations with other telescopes
• Development of variability models continues at
  Metsähovi
• Statistical analysis of the IDB candidates

13
EGRET detections of AGNs

• 66 high-confidence identifications of AGNs
• 27 lower-confidence identifications of AGNs
• (Hartman et al., 1999)
• Practically all are bright and variable in the
  millimeter domain (Tornikoski et al., 2002)
• But not all bright and variable AGNs were
  detected with EGRET...

14
Gamma-ray activity

• The most probable AGN to be detected in
  gamma-rays is a source with..
• an ongoing and still rising high-frequency radio
  flare
• an inverted/flat spectrum up to 100 GHz during
  the active state (Tornikoski et al., 2002)
• gt IDBs?!
• Radio observations as a ToO tool for gamma
  instruments
• The beginning of a radio flare, the formation of
  a new radio shock seems to correlate with the
  gamma activity