An Accretion Disk Laboratory in the Seyfert Galaxy NGC 2992

Tahir Yaqoob (JHU/GSFC)

with Kendrah Murphy (JHU/GSFC), & the Suzaku Team.

Some of this work is based on Suzaku data: paper submitted to PASJ:

Overview

Brief summary of diagnostics of accretion onto supermassive black holes in the X-ray band.

More than twenty five years of X-ray observations of the Seyfert 1.9 galaxy NGC 2992: New results from historical data, new Suzaku observations and a one-year RXTE monitoring campaign.

NGC 2992 exhibits large-amplitude (>20), SLOW X-ray variability.

This allows excellent characterization of the spectrum in each state: accretion disk (AD) models must explain the variability AND non-variability of spectral features.

We find a complex and variable Fe K line profile and an essentially constant X-ray spectral shape, severely constraining AD models.

Narrow Fe K Line

AGN X-ray Spectral Diagnostic Features

In type 1.5-2 AGN direct l.o.s. absorptionmay make the broad Fe K disk line hard todetect. Also, absorption extinguishes the low-energy X-ray spectrum but then possibleoptically-thin thermal emission and/or scattering from an extended warm electrongas may dominate the soft X-ray spectrum.

Origin of the Hard X-rays

The geometry is uncertain, but it is likely that soft thermal photons from AD areupscattered by electrons in a hot corona (temperature, kT~30-300 keV; optical depth, ~0.1-1).

X

AD

AD

Fe K & Reflection Features

Disk-line and distant-matter lines must be deconvolved.. usually there can be considerable ambiguity.

AD

Deconvolution of the Fe K emission line from the accretion disk & distant matter is difficult even with Chandra HETG & has only been done for a few cases. Some Fe K line profiles show complexity due to lines from highly ionized Fe, which are becoming increasingly common (e.g. see Bianchi et al. 2004).

NGC 4051:Black: Chandra HETGRed: non-simultaneousASCA.

Left: NGC 4051 Disk Fe-K line intensity vs. narrow distant-matter line intensity from HETG data.

Right: IC 4329a Fe K complex:Fe Ly? McKernan & Yaqoob 2004.

IC 4329a

NGC 2992: An SBH Accretion Disk Laboratory

NGC 2992: one of the original Piccinotti et al. (1982) hard X-ray selected AGN. In >25 years of X-ray observations NGC 2992 shows long-term, large amplitude variability (a factor >20) of the hard X-ray (e.g. 2-10 keV) flux. Did NGC 2992 undergo a long-term diminishing of accretion (on a timescale of years) and then a “rebuilding” of the disk?

The 2-10 keV flux covers a range ~0.4-9.5 x 10-11 erg cm-2 s-1 and the luminosity ~0.5-13 x 1042 ergs s-1. Includes 3 new observations with Suzaku (quasi-simultaneous with RXTE).

Classically, NGC 2992 is a Seyfert 1.9 galaxy, but shows optical broad lines when very active ( i.e. at the high end of the luminosity range).

NGC 2992 is nearby, (z=0.00771), and has a low Galactic column (5.26 x 1020 cm-2). NGC 2992 shows complex behavior of the Fe K line: it probes accretion disk & distant

matter and recent analysis of all the data yields some new results. All of this behavior is very reminiscent of NGC 4151.

NGC 2992: An SBH Accretion Disk Laboratory

NGC 2992: one of the original Piccinotti et al. (1982) hard X-ray selected AGN. In >25 years of X-ray observations NGC 2992 shows long-term, large amplitude variability (a factor >20) of the hard X-ray (e.g. 2-10 keV) flux. A recent ~1 yr RXTE campaign showed that a dynamic range in hard flux of a factor ~10 is achieved on a timescale of weeks, and this happened a few times in the campaign.

The 2-10 keV flux covers a range ~0.4-9.5 x 10-11 erg cm-2 s-1 and the luminosity ~0.5-13 x 1042 ergs s-1. Includes 3 new observations with Suzaku (quasi-simultaneous with RXTE).

Classically, NGC 2992 is a Seyfert 1.9 galaxy, but shows optical broad lines when very active ( i.e. at the high end of the luminosity range).

NGC 2992 is nearby, (z=0.00771), and has a low Galactic column (5.26 x 1020 cm-2). NGC 2992 shows complex behavior of the Fe K line: it probes accretion disk & distant

matter and recent analysis of all the data yields some new results. All of this behavior is very reminiscent of NGC 4151.

Fe

NGC 7314: Yaqoob et al. 2003

NGC 2992 SAX1 (LOW) NGC 2992 SAX2 (HIGH)

In the low state NGC 2992 does not showshort-timescale variability but it does in thehigh state. Contrast with e.g. NGC 7314.

NGC 2992 Historical Spectra

SAX2 MECS

SAX2 PDS

XMM pn

Suzaku XIS

HXD PIN

MECS PDS

SAX2

ASCA SIS

ASCA 1994SAX1 1997SAX2 1998XMM 2003Suzaku 2005

NGC 2992: An SBH Accretion Disk Laboratory

Slow (timescale ~years) “rebuilding” of the AD isruled out!

Suzaku XIS data for NGC 2992

Summed XIS data for 3 observations in Nov-Dec2005. Left: absorbed power-law plus scatteringmodels. Below: (a) Fe K line profile; (b) Narrowlines removed showing a broad Fe K line profile.

NGC 2992 Suzaku Data: Baseline Model

Disk Line deg.Compton-thin: lg(NH) ~ 22

Suzaku XIS CCDs deconvolve the disk & distant-matter Fe K lines in NGC 2992 for the first time! Thus far this has only been possible in a few AGN.

Moreover, NGC 2992 was in a LOW STATE!

NGC 2992: Comparison with attempts at the Fe K line complex deconvolution from previous data.

ASCA (1994)

SAX1 (1997)SAX2 (1998)XMM (2003)Suzaku (2006)

Left: NGC 2992, Suzaku XIS, EW of Fe K line core vs. FWHM. Not corrected for resolution degradation (corrected upperlimit is FWHM~ 4090 km/s).

Right: NGC 2992, Suzaku XIS, Reflection fraction vs. inclination angle of the disk (including disk line).

Unprecedented precision in constraining the ionization state of Fe responsible for the narrow XIS Fe K line due to the redundant information provided by the high SNR Fe Kline. States higher than Fe VII are ruled out after conservatively accounting for instrumental and theoretical uncertainties.

Fe I

Fe IX

Fe VIII [+/- 2 mA]

Historical Fe K line profiles compared with the Suzaku Fe K line core.

The Suzaku line model was folded through the instrument responses, keeping the line intensity fixed, but fitting for the continuum.

Left: Counts spectra compared with the Suzaku line model (red).

Right: As left-hand plots but shown in the form data/model.

The ASCA line (1994) is consistent the Suzaku line core but a broad line commensurate with the low continuum level is not ruled out.

The SAX1 (1997), SAX2 (1998), & XMM (2003) spectra show a complex and variable Fe K line profile, probably originating in the accretion disk.

The accretion disk line appears to vary dramatically, particularly the ionization state in SAX1. The RXTE continuum variability does not support the slow, rebuilding of the accretion disk scenario.

NGC 2992 1-year RXTE monitoring

Significantly redshifted Fe K line centroid energy in high state.

High

Low

Implication of RXTE Fe K line variability in NGC 2992: violent activity of the continuum restricted to the inner accretion disk.

Similar behavior was once seen by ASCA in MCG -6-30-15 (Iwasawa et al. 1999).

High state: constraint on outer disk radius of flare activity from redshifted Fe K line.

NGC 2992Dual line model

RXTE high state

RXTE low state:RED: Disk Line fixed to high-state, Rout free;BLUE: Disk Line free, Rout fixed to high-state

MCG -6-30-15

NGC 2992

NGC 2992 RXTE 1-year monitoring: the continuum shape Large amplitude (factor ~10 or more) variability in the continuum luminosity &

accretion power, accompanied by NO significant variability in the hard X-ray power law slope. In a thermal Comptonization scenario, this implies an approximately constant Compton-y parameter. It is likely that kT & are both nearly constant (note < ~1-2 or else kT is too low) - soft L drives variability.

Black: High StateBlue: Low State[99% confidence]

Summary In NGC 2992 LX varies by >20 over a >25 yr history.

L/LEdd is ~ 0.00065 to 0.015. ~1 yr of RXTE monitoring showed an order of magnitude variability, on

timescales of weeks: “rebuilding” scenarios on timescales of years for the accretion disk are ruled out.

The RXTE campaign showed that the high states were confined to violent activity in the inner disk, evidenced by the appearance of a gravitationally redshifted, broad Fe K line.

Suzaku deconvolved a broad Fe K line from the narrow distant-matter line, despite the source being in a low state.

Other historical data are ambiguous on the broad Fe K line due to problems with deconvolution. A low-state BeppoSAX spectrum showed an additional ionized Fe K line component.

During the large-amplitude X-ray luminosity excursions, the intrinsic X-ray spectrum maintains essentially a constant shape. Contrasts with GBH. In a thermal Comptonization scenario this translates to an approximately constant Compton-y parameter.

Accretion Disk models must accommodate all of the observational constraints in NGC 2992. Further questions remain - frequent monitoring with good energy resolution and high-energy coverage is required.