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NGC 3147: a 'true' type 2 Seyfert galaxy without the broad-line region

Stefano Bianchi. NGC 3147: a 'true' type 2 Seyfert galaxy without the broad-line region. A. Corral 1 , F. Panessa 1,2 , X. Barcons 1 , G. Matt 3 , L. Bassani 4 , F.J. Carrera 1 , E. Jiménez-Bailón 5 , F. La Franca 3 , N. Sacchi 3

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NGC 3147: a 'true' type 2 Seyfert galaxy without the broad-line region

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  1. Stefano Bianchi NGC 3147: a 'true' type 2 Seyfert galaxy without the broad-line region A. Corral1, F. Panessa1,2, X. Barcons1, G. Matt3, L. Bassani4, F.J. Carrera1, E. Jiménez-Bailón5, F. La Franca3, N. Sacchi3 1Instituto de Física de Cantabria (CSIC-UC) - Santander (Spain)‏ 2INAF-IASF - Roma (Italy)‏ 3Università degliStudidi Roma TRE - Roma (Italy)‏ 4INAF-IASF - Bologna (Italy)‏ 5Universidad NacionalAutónoma de México, Mexico DF (Mexico)‏ THE X-RAY UNIVERSE 2008- Granada, May 28th 2008

  2. Narrow Lines No broad lines Type2 AGN: The Unification Model view Optical NLR BLR BLR Torus

  3. Type2 AGN: The Unification Model view X-rays C-thin NLR C-thick BLR Absorber X-rays and optical classifications generally agree: large amounts of X-ray absorption are measured in Seyfert 2s BLR Torus

  4. Risaliti et al. (2007)‏ In some cases, the classifications in the two bands do not match the expectations of Unified Models. However, this mismatch is often due to the fact that the observations in the two bands are not simultaneous and catch the source in different states. These 'changing-look' AGN may be explained by a 'switching-off' of the nucleus or by a variable column density of the absorber. Matt et al. (2003)‏ The key to find genuine 'unabsorbed Seyfert 2s' is represented by SIMULTANEOUS X-ray and optical observations

  5. We selected a conservative subsample of 5 sources, taken from Panessa & Bassani (2002). It includes optical Seyfert 2 galaxies without X-ray absorption and excluding Compton-thick candidates The Sample 2 sources were observed 1 will be observed this year

  6. NGC 3147 z=0.009 The pn and MOS spectra are well fitted by a powerlaw (~1.6) absorbed by the Galactic column density, plus a neutral iron K line (EW~130 eV)‏ NGC3147 is absorbed by a very low local column density. NH< 5x1020 cm-2 (99% for two parameters)‏

  7. Adapted from Panessa & Bassani (2002)‏ NGC3147 is NOT Compton-thick: - Neutral iron Ka EW: ~130 eV - X-ray/IR/[OIII] flux diagrams

  8. NGC3147: Optical spectrum NO BROAD Ha or Hb! The flux of any broad component of the Ha would be at most 5% of the total Ha flux The lack of broad optical lines in NGC3147 is an intrinsic property of the source and not an artefact of low S/N

  9. The X-ray spectrum of NGC3147 is that of a typical type 1 AGN -No absorption -G~1.6 -Iron Ka EW~130 eV -aox ~ 1.33 The SIMULTANEOUS optical spectrum confirms the lack of broad permitted lines! The very low column density measured in the X-rays (NH< 5x1020 cm-2) corresponds to AV<0.3, at odds with the large amount of dust required to obscure the BLR NGC3147 intrinsically lacks the BLR! Low luminosity Low accretion rate Below a minimum accretion rate, the BLR cannot form (Nicastro 2000)‏ The Eddington ratio of NGC3147 ranges between 8x10-5 and 2x10-4, well below the 'threshold' proposed in this scenario The BLR may disappear at very low bolometric luminosities (Elitzur & Shlosman 2006)‏ The bolometric luminosity of NGC3147 is about 5x1042 erg s-1, larger than the 'threshold' calculated in this scenario Moreover, in this case the lack of the BLR would imply the lack of the torus

  10. IC 1631 z=0.031 The XMM-Newton spectrum has a very low flux: F2-10kev=(2.8±1.1)x10-14 cgs and a very low luminosity: L2-10kev=(6.2±2.4)x1040 cgs The previous (and only) X-ray observation was performed by GINGA and was likely contaminated by Abell 2877 (Awaki 1993)‏ Its flux was to be considered an upper limit: F2-10kev< 1.0x10-11 cgs The very low flux ratio Fx/F[OIII]~ 0.05 suggests that IC1631 is a Compton-thick AGN or a starburst In any case, it cannot be considered an unabsorbed Seyfert 2 candidate any more!

  11. Adapted from Panessa & Bassani (2002)‏ IC 1631 z=0.031 The optical lines' ratios points to a starburst classification

  12. Conclusions The X-ray spectrum of NGC3147 is that of a typical type 1 AGN (NH< 5x1020 cm-2)‏ The simultaneous optical spectrum excludes the presence of broad components for Ha and Hb The key parameter for the observational properties of this source cannot be orientation, but an intrinsic feature (be it low accretion rate or luminosity), which prevents the BLR from forming. Bianchi et al., 2008, MNRAS 385, 195 NGC3147 is the first 'true' type 2 Seyfert galaxy without the BLR IC1631 is a starburst galaxy and must therefore be removed from the list of 'unabsorbed Seyfert 2' candidates The key to find genuine 'unabsorbed Seyfert 2s' is represented by SIMULTANEOUS X-ray and optical observations Seealso Francesca Panessa’s poster!

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