X-ray spectroscopy Workshop

1
On the origin of soft X-rays in obscured AGN
Stefano Bianchi
Matteo Guainazzi
X-ray spectroscopy Workshop Cambridge (MA,
U.S.A.) - Thursday, July 12th 2007
2
The 'soft X-ray excess' is almost ubiquitous in
Seyfert 2s and cannot be completely attributed to
starburst emission
The key to understand its nature is HIGH
RESOLUTION SPECTROSCOPY
3
NGC1068
Strong emission lines dominates! No continuum ?
log(NH )lt22.7
XMM RGS
Kinkhabwala et al. 2002
4
NGC1068
Kinkhabwala et al. 2002
5
XMM-Newton 190 ks combined RGS spectrum
Mrk3
The high resolution spectrum of Mrk3 is
unambiguously produced in a photoionized gas
-K lines dominant over Fe L -RRCs Resonant
scattering is important -Fe L 3d-2p/3s-2p ratio
-K resonant/ forbidden ratio
Bianchi et al. 2006
6
(No Transcript)
7
What about the other Sy2s?
Most RGS spectra of Sy2s are dominated by
emission lines with low or no continuum Often,
most of the soft excess is concentrated in
single, very strong lines which can be easily
detected even in sources with very low SNR spectra
Guainazzi Bianchi, 2007
8
We produced the first catalogue of soft X-ray
emission lines in a sample which includes all the
type 1.5 AGN observed by XMM-Newton
RGS CIELO-AGN Catalogue of Ionized Emission Line
Obscured AGN
Guainazzi Bianchi, 2007

• 69 objects
• ltF0.1-2 keVgt ? 10-13 cgs
• OVIII Lya detected in ?50 of the sample
• OVII triplet in ?40
• Many other lines from O, Fe, C, Si, Mg, Ne, N
  detected in ?15

9
CIELO confirms the results derived from the
analysis of the brightest sources

• RRCs are
• Common (detected in 40 o.t.s.)
• Narrow (??10 eV)
• ?
• Photoionization

Guainazzi Bianchi, 2007
10
(No Transcript)
11
Where is this gas located?
A close association between the soft X-ray
emission and the NLR (traced by OIII) is
observed both on large and small scale
12
What is this gas?
Bianchi et al., 2007
The comparison between the Chandra and the HST
images shows that the OIII/soft X-ray ratio is
fairly constant along with the radius, up to
hundreds of pc. Photoionization models reproduce
this behavior if ne?r-?, with ??2 (i.e. constant
ionization parameter). This is in agreement with
NLR emission line ratios (e.g. Kraemer et al.
00, Kraemer Crenshaw 00, Bradley et al. 04,
Collins et al. 05).
13
What about the starburst contribution?
Jiménez-Bailón et al. 2003
NGC7130
NGC4303
HST
Chandra
3 pc
110 pc

• In the immermost 110 pc
• low luminosity AGN LX1039 erg s-1
• young stellar cluster LX61038 erg s-1

Levenson et al. 2005
14
So AGN or starburst?
15
of course this is too simple
NGC7582
Bianchi et al., 2007
16
Conclusions

• High-resolution spectroscopy IS fundamental to
  understand the physical properties of the gas in
  the AGN circumnuclear environment (as
  high-resolution imaging IS fundamental to unveil
  its true location)

• In obscured AGN, CIELO unveils mounting evidence
  for
• Dominant role of AGN-photoionization,
• Important role of resonant scattering,
• Broadly constant ionisation parameter ...
• on scales as large as a few hundreds parsec

• CIELO unveils a criterion to discriminate between
  AGN- and starburst-dominated sources on the basis
  of the OVII(f)/OVIII ratio