X-ray spectroscopy of bright Seyfert 2s: The importance of the 10-100 keV spectrum

Guido RisalitiINAF - Arcetri Observatory, Italy

&Harvard-Smithsonian Center for Astrophysics

- One Case study: XMM observations of NGC 1365- Time-resolved NH variability: current limits- The impact of Simbol-X

Outline

NGC 1365: The best laboratory to investigate the absorber in obscured AGN

Hard X-ray observations:

ASCA (1995) 40 ksBeppoSAX (1997) 30 ks Chandra (Dec 2002) 15 ksXMM 1 (Jan 2003) 17 ksXMM 2 (Jan 2003) 10 ksXMM 3 (Aug 2003) 15 ks XMM 4 (Jan 2004) 60 ksXMM 5 (Aug 2004) 60 ks

Chandra (Apr 2006):6 x 15 ks

(Risaliti et al. 2007, ApJ 659, L11)

NGC 1365: Two XMM long observations

Spectral analysis of XMM long observations2. Relativistic Iron Line

One of the best cases, only (?) strong case in high NH sources

Disappearing in obscured spectrum --> within 1014 from the center

Intra-day NH variations XMM 4: 60 ks

New analysis: -10 time intervals, 6 ks each-Constant continuum + (a) free NH for each spectrum (b) two NH (the same for all spectra) and free covering factor of NH2

Short-time column density variability

T = 25 ksD ~ 3x1013 cm

NH1=1.1x1023 cm-2

NH2=3.0x1023 cm-2

Only) other know case: NGC 4151 observation with BeppoSAX

Puccetti et al. 2007

Simbol-X simulations:

T = 6 ksec

NH=2x1023 cm-2

E(NH) ~ 20%

E(NH) ~ 6%

XMM (var. cont.):

E(NH) ~ 6%XMM (const cont.):

Conclusions

- Short timescale (~5-10 ksec) column denisty variability may be common in Seyfert Galaxies

-Resolving the NH variability is crucial to understand the structure of the circumnuclear absorber AND to obtain a correct fit of the other spectral components

-High quality 10-50 keV spectra needed to unambigously detect NH variability: Simbol-X capable to completely remove degeneracy between spectral parameters in bright Seyfert Galaxies