NGC 3147: a 'true' type 2 Seyfert galaxyNGC 3147: a 'true' type 2 Seyfert galaxywithout the broad-line regionwithout the broad-line region

THE X-RAY UNIVERSE 2008- Granada, May 28th 2008

Stefano BianchiStefano Bianchi

A. CorralA. Corral11, F. Panessa, F. Panessa1,21,2, X. Barcons, X. Barcons11, G. Matt, G. Matt33,,L. BassaniL. Bassani44, F.J. Carrera, F.J. Carrera11, E. Jiménez-Bailón, E. Jiménez-Bailón55,,

F. La FrancaF. La Franca33, N. Sacchi, N. Sacchi33

11Instituto de Física de Cantabria (CSIC-UC) - Santander (Spain)Instituto de Física de Cantabria (CSIC-UC) - Santander (Spain)22INAF-IASF - Roma (Italy)INAF-IASF - Roma (Italy)

33Università degli Studi di Roma TRE - Roma (Italy)Università degli Studi di Roma TRE - Roma (Italy)44INAF-IASF - Bologna (Italy)INAF-IASF - Bologna (Italy)

55Universidad Nacional Autónoma de México, Mexico DF (Mexico)Universidad Nacional Autónoma de México, Mexico DF (Mexico)

BLR

Narrow Lines

No broad lines

Type2 AGN:The Unification Model view

NLR

BLR

Torus

Optical

BLR

Type2 AGN:The Unification Model view

NLR

BLR

Torus

Absorber

C-thin

C-thick

X-rays

X-rays and optical classifications

generally agree: large amounts of X-ray

absorption are measured in Seyfert

2s

The key to find genuine 'unabsorbed Seyfert 2s' is The key to find genuine 'unabsorbed Seyfert 2s' is represented by SIMULTANEOUS X-ray and optical represented by SIMULTANEOUS X-ray and optical

observationsobservations

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.

Risaliti et al. (2007)

Matt et al. (2003)

The SampleThe Sample

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

2 sources were observed1 will be observed this year

Source XMM-Newton Optical observation

NGC 3147 NGC 3147 Oct. 6Oct. 6thth 2006 2006 Oct. 4Oct. 4thth,5,5thth,9,9thth 2006 (OSN)2006 (OSN)

IC 1631IC 1631 Nov. 23Nov. 23thth 2006 2006 Dec. 1Dec. 1stst 2006 2006 (ESO)(ESO)

IRAS 01428-0404 AO7 Tbd

Mrk 273xMrk 273x ?? ??

NGC 4698NGC 4698 ?? ??

NGC3147 is absorbed by a very

low local column density.

NH< 5x1020 cm-2

(99% for two parameters)

NGC 3147NGC 3147z=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 NOT Compton-thick:NGC3147 is NOT Compton-thick:

- Neutral iron EW: ~130 eV- X-ray/IR/[OIII] flux diagrams

Adapted from Panessa & Bassani (2002)Adapted from Panessa & Bassani (2002)

NO BROAD HNO BROAD H or H or H!!The flux of any broad component of the H would be at

most 5% of the total H fluxThe lack of broad optical lines in NGC3147 is an intrinsic

property of the source and not an artefact of low S/N

NG

C3147:

Opti

cal sp

ect

rum

The X-ray spectrum of NGC3147 is that of a typical type 1 AGN

-No absorption-~1.6

-Iron K 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!NGC3147 intrinsically lacks the BLR!

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

Low luminosityBelow 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

Low accretion rate

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 ratioFx/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 2candidate any more!

IC 1631IC 1631z=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

IC 1631IC 1631z=0.031

Adapted from Panessa & Bassani (2002)Adapted from Panessa & Bassani (2002)

The optical lines' ratios points to a starburst classificatio

n

ConclusionsConclusionsThe 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 H and H

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.

NGC3147 is the first 'true' type 2 Seyfert NGC3147 is the first 'true' type 2 Seyfert galaxy without the BLRgalaxy 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

Bia

nch

i et a

l., 2008, M

NR

AS

385,

Bia

nch

i et a

l., 2008, M

NR

AS

385,

195

195

See alsoSee alsoFrancesca Francesca Panessa’sPanessa’s

poster!poster!