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chandra grating spectroscopy of active galactic nuclei tahir yaqoob jhu gsfc
Chandra Grating Spectroscopy of Active Galactic NucleiTahir Yaqoob (JHU/GSFC)


B. McKernan (UMD), C. Reynolds (UMD), I. M. George (UMBC/GSFC), T. J. Turner (UMBC/GSFC), J. N. Reeves (USRA/GSFC), P. J. Serlemitsos (GSFC), R. F. Mushotzky (GSFC), S. B. Kraemer (CU/GSFC), M. Crenshaw (GSU), J. Gabel (CU/GSFC), U. Padmanabhan (JHU), V. Karas, M. Dovciak (Charles U., Prague), A. Markowitz (GSFC)

  • The Chandra grating data and general overview of salient results.
  • Results from a Chandra HETG sample of Sy 1 galaxies.
  • Properties of the photoionized outflows & a comparison with other results including XMM RGS. Location of the wind.
  • Gravitationally redshifted lines. Extreme outflows. Absorption in the IGM.
  • Emission lines, including Fe K.
  • What can Suzaku do for AGN winds?
  • A HETG AGN database of ready-to-go products, suitable for grating non-experts (and experts).


  • best resolution at lowest
  • energies
  • LETG: ~240 km/s at 0.2 keV [0.16 eV]
  • MEG: ~280 km/s at 0.5 keV [0.47 eV]
  • RGS: ~290 km/s at 0.3 keV [0.29 eV]




E (keV)

x ray absorption in ionized gas in seyfert 1 galaxies
X-ray Absorption in Ionized Gas in Seyfert 1 Galaxies
  • Before Chandra & XMM, CCDs had best spectral resolution (FWHM ~30,000 -10,000 km/s in soft X-rays, 7,500 at Fe-K energies).
  • ~50% of Sy 1 known with complex (likely photoionized) X-ray absorption.
  • Individual O edges claimed but could have been confused.
  • Chandra & XMM gratings, with FWHM down to ~300 km/s, revolutionalized study of “warm absorbers”, wealth of complexity, unresolved absorption lines, some emission lines.

Pre-1999 View

what do we see
What Do We See?

Mostly He-like, H-like unresolved absorption lines; in most

cases blueshifted w.r.t. to systemic (~0-1000 km/s FWHM).

Mkn 509 Chandra HETG+HST STIS campaign [Yaqoob et al. 2003]

Derived column density from X-ray (Chandra LETGS) data versus the ionization parameter for which that ion has the maximum column density.

NGC 5548 (Steenbrugge et al. 2003)

dust vs relativistic lines
Dust vs. Relativistic Lines

MCG -6-30-15 soft X-ray spectrum: (Left) Lee et al. 2001 Dusty Warm Absorber;

(Right) Relativistically broadened soft X-ray lines, K. Mason & others, 2001..2005

Soft X-ray broad lines also claimed in NGC 4051 (Ogle et al. 2004), NGC 5548 (Kaastra et al.

2002), MCG -2-58-22 (Salvi et al. 2003), NGC 4593 (Steenbrugge et al. 2003)

mcg 6 30 15 chandra hetg 500 ks long look young et al 2005
MCG -6-30-15Chandra HETG ~500 ks “long-look”(Young et al. 2005)
  • Fe K absorption features found (~2000 km/s outflow)..absorber model for broad Fe K line predicts Fe K absorption features not found?
  • Caution..the Fe K absorption features found could be at z~0.
ton s 180 letg acis

Turner et al. 2002

Rozanska et al. 2004

  • Weak absorption features..alternative models
  • proposed: No warm absorber plus relativistic
  • lines (Turner et al. 2002); Stratified warm absorber
  • (with identified weak lines) plus disk emission lines
  • (Rozanska et al. 2004).
  • Very few LETG/ACIS observations. More

LETG/HRC observations (but orders can’t be

separated), but still much less than HETG/ACIS.


Details of a physical

model need to be filled

in. Multi-temperature

wind (cf. Krolik & Kriss

2001)? What drives it &

what is the source of the


  • X-ray/UV connection
  • X-ray & UV absorbers share kinematics
  • Much higher resolution in UV - why discrete components?
  • Hints of velocity structure in some X-ray profiles, details elusive.
  • Very different UV & X-ray columns (but e.g. Arav et al. ‘04: UV columns much larger?).
  • Two-phase? UV “knots” in an X-ray wind?

From Kaspi et al. 2002, & Crenshaw, Kraemer & George 2003, AR&AA, 41, 117

a chandra hetg sample of seyfert 1 galaxies
A Chandra HETG Sample of Seyfert 1 Galaxies

What we want to know:

  • Where does the outflow originate?
  • What is its size? Geometry?
  • Physical, thermal, & ionization structure? Kinematics?
  • Source of material in the wind?
  • What determines properties of the outflow?
  • What is the nature of the connection between the outflow and the central black hole plus accretion disk?
  • Covering factor/filling factor?
  • What drives the outflow?
  • Mass outflow rate (compare to accretion)?

Urry & Padovani 1995

Test for correlations between

outflow properties & other key

properties of the central engine.

a chandra hetg sample of seyfert 1 galaxies1
A Chandra HETG Sample of Seyfert 1 Galaxies
  • Selection:
  • Low z (<0.05) Seyfert 1 galaxies
  • Public HETG data up to 1 July, 2003
  • Bright (HEG > 0.05 ct/s)
  • -> 15 AGN; 10/15 exhibit signatures of ionized absorption. (Detailed results in McKernan, Yaqoob, Reynolds 2004, 2005, 2006)
  • What we can measure:
  • Columns, ionization parameters from modeling; offset velocities of absorption lines; crude kinematic information (widths, profiles).
  • If sufficient emission-line data, density. Cannot get distance from center without density or variability information.
  • UV absorption: 4 of the 15 have simultaneous UV/Chandra data. How are UV/X-ray columns, ionization parameters, covering factors and kinematics related?
correlations with outflow velocity l ion l edd
Correlations with Outflow Velocity & LION/LEDD

McKernan, Yaqoob, & Reynolds 2006






  • V appears to have a bimodal distribution. Anti-correlated with LION/LEDD?
  • No correlation of N with LION/LEDD . Possible anti-correlation of x with LION/LEDD.

V (km/s) LION/LEDD

correlations with black hole mass l ion l edd
Correlations with Black Hole Mass & LION/LEDD

McKernan, Yaqoob, & Reynolds 2006

MOUTFLOW [ 0.01 C MSOLAR / year ]

  • Appears to be no correlation between mass outflow rate and black-hole mass.
  • Possible correlation of mass outflow rate with LION/LEDD .


blustin et al 2005 study outflow rates
Blustin et al. (2005) study: outflow rates

These mass ouflow rates are LARGE, often greater than the accretion rate..but the absolute outflow rates depend on assumptions (Ne, covering & filling factors, and distance to the ionizing source have to be inferred, usually indirectly, based on assumptions which may or may not be true).

comparison with blustin et al conclusions
Comparison with Blustin et al. Conclusions
  • Low filling factor (<8%), derived assuming momentum in outflow ~ momentum in radiation intercepted.
  • Minimum distance of warm absorber calculated assuming outflow exceeds escape velocity - not necessarily true. Leads to conclusion that the absorbers are located at ~ distance of torus or greater.
  • Kinetic energy of outflow may only be 1% of total energy budget, but so is the accretion rate. If the accretion rate is small yet important for the AGN then the outflow could be too.
  • Another caveat: Some of the outflow (e.g. closer in to center) may not be observable (e.g. too ionized).
location of the wind
Location of the Wind
  • Need variability information (continuum and opacity) to constrain the density and hence the location of the photoionized absorber. Any other method of deriving location makes at least one assumption, which may or may not be true.
  • Early variability studies (e.g. NGC 3227 Ptak et al. 1994; MCG -6-30-15, Reynolds et al. 1995; NGC 4051, McHardy et al. 1995; MR 2251, Otani et al. 1995; NGC 3516, Netzer et al. 2002) with low-resolution (CCD, or PSPC) spectra are difficult to interpret since the spectra are now known to be very complex.
  • Estimates of the location of the “warm absorber” varied from upper limits of parsecs to the distance of the BLR (e.g. NGC 3516).
  • From different arguments, location of the very high velocity outflows (e.g. PG1211+143), placed at <0.1pc (more later).
  • S/N ratio of the higher resolution grating spectra has been too low for time-resolved spectroscopy..except for the extended Chandra HETG observation of NGC 3783…
opacity variations in the fe uta in ngc 3783
Opacity Variations in the Fe UTA in NGC 3783
  • 0.2A shift in UTA, x2 change in U with x2 change in L -> photoionization eqm., Ne>104 cm-3, d<6pc. LP only. HP does not respond (e.g. 8-13A). Var. result claimed at >10s.

Krongold et al. 2005

picture and structure of the wind
“Picture” and Structure of the Wind
  • Does the wind originate from the accretion disk (e.g. Elvis 2000, 2003)?
  • Or does it originate in material blown off from the inner edge of the torus (e.g. Krolik & Kriss 2001- gas exists in a multi-phase, multi-temperature state in pressure balance but on the thermally unstable part of the cooling curve.)? Mass flux could be large.
  • Large scale cones (of the type directly observed in Sy 2) [e.g. Kinkhabwala 2002].
  • High resolution X-ray spectra have lead to the view of a wide, radially continuous range of ionization stages of ions.
  • Krongold UTA variability result rules out continuous ionization stage distribution, favoring high degree of clumping.
  • Also rules out kpc scale cone scenario.

E1821+643 (z=0.297)

Evidence for a

gravitationally redshifted

absorption line, and one the highest

redshift broad Fe-K emission lines.

Yaqoob & Serlemitsos, 2005

redshifted absorption lines in pg 1211 143
Redshifted Absorption Lines in PG 1211+143
  • Redshifted absorption lines at 4.56 & 5.33 keV rest-frame (z=0.0809);

~1.3 x 10-4 chance probability. FWHM<8000 km/s.

  • If Fe XXVI, v~0.26c & 0.40c (0.22 & 0.37c for Fe XXV).
  • Column density is ~4 (+4,-2) x 1023 cm-3, but Fe K edge depth < 0.1. logx ~ 4 .
  • Pure gravitational shift?[R<6Rg]; Inflow/Failed outflow? Or gravitationally redshifted low-velocity outflow?
Extreme Outflows
  • XMM CCD detections of very high-velocity outflows deduced from (blueshifted) Fe-K absorption lines from highly ionized Fe in some QSOs (Pounds, Reeves et al. 2003..).
  • PG 1211+143: v~ 24,000 km/s
  • PG 0844+349: v~ 60,000 km/s
  • High optical depths: NH~ 5 x 1023 cm-2 or more..but model-dependent.
  • Other examples: PDS 456 (v~55,000 km/s).
  • These are moderately low redshift QSOs (z<0.2).
  • NOTE: Alternative interpretation of PG1211+143 by Kaspi et al. (2005) is an outflow with V~3000 km/s, due mainly to alternative line ids plus a detailed model which has emission lines which “fill in” some of the absorption lines.
search for local z 0 ovii oviii absorption in the hetg agn sample
Search for local (z~0) OVII & OVIII Absorption in the HETG AGN sample

Search for WHIGM: McKernan, Yaqoob, & Reynolds (2004, ApJ, 617, 232).

+ No whigm detected; Ovii & Oviii detected but no FUSE observations;

Ovii & Oviii detected AND Ovi detected with FUSE.

are the extreme outflows due to whigm
Are the Extreme Outflows Due to WHIGM?
  • Local (z~0) OVII absorption from HETG Seyfert 1.

PDS 456

3C 273

PKS 2155

PG 1211+143

Mkn 421

  • Outflows not claimed in 3C 273, PKS 2155, & Mkn 421.
  • “Outflow” in NGC 4051 with V ~ 600 km/s may be due to local absorption.
  • Large columns in PG1211+143 & PDS456 make WHIGM interp. very difficult.
are the extreme outflows due to whigm1
Are the Extreme Outflows Due to WHIGM?

PG 0844+349

  • Local (z~0) OVII absorption from HETG Seyfert 1.

PDS 456

3C 273

PKS 2155

PG 1211+143

Mkn 421

PG 0844+349 does NOT fit on the correlation. The outflow velocity required (from modeling XMM data-Pounds et al. 2004), is ~60,000 km/s, much larger than cz~20,000 km/s.

most outflows

narrow emission lines


NGC 5548 OVII triplet

Narrow Emission Lines
  • In the McKernan et al. Sample, prominent emission lines are seen in NGC 3783, NGC 5548, NGC 4051.
  • Weaker emission lines are seen in MCG -6-30-15, NGC 4593, Mkn 509, & Mkn 279.
  • Emission lines are much less common than absorption lines in Sy 1 (but soft X-ray spectra of Sy 1.5-2 are line-dominated, e.g. NGC 4151).
  • In general the emission lines are centered on the systemic velocity of the system.
hetg fe k lines
HETG Fe K Lines
  • Fe K line studied for same HETG sample of Sy 1, in Yaqoob & Padmanabhan (2004).
  • A narrow, often unresolved core at 6.4 keV in the rest frame is common, but some of the AGN HETG Fe K lines show complexity with the high spectral resolution of the Chandra high-energy gratings.
peak energy fwhm of fe k line core
Peak Energy & FWHM of Fe-K Line Core

Mean peak energy:

6.404 +/- 0.005 keV

HEG resolution

is ~1800 km/s


HETG sample of 15

Sy 1 galaxies. Yaqoob &

Padmanabhan 2004.

Mean FWHM:

2380 +/- 760 km/s

At least 8/15

have a broad

line. Core

resolved in 3/15.

correlation of ionized outflow parameters with the ew of the fe k line core
Correlation of Ionized Outflow Parameters with the EW of the Fe-K Line Core




HETG sample of 15

Sy 1 galaxies: Fe-K core EW from Yaqoob & Padmanabhan 2004.

Warm absorber (outflow) parameters from McKernan, Yaqoob & Reynolds (2006).


Ionization balance of Fe (as manifested

by the emission line complex between

Fe I and Fe XXVI), responds rapidly

to the continuum variability (1000s of

seconds or less).

See Yaqoob et al. (2003).


MCG -6-30-15





suzaku resolves c o lines in the planetary nebula bd 30 3639 for the first time
Suzaku resolves C, O lines in the Planetary Nebula BD+30 3639 for the first time



  • C/Ne ~ 4 -10
  • C/O ~ 30-100
  • N/C ~ 0



Chandra ACIS: C, O lines


Suzaku BI CCD

Suzaku Team/K. Arnaud/K. Makishima

How does the better low-energy spectral resolution of the XIS BI chip help with studying the warm absorber or wind, compared to Chandra or XMM?
  • Effective area of the XIS BI chip is much higher than that for the gratings. However, XIS BI is better than XMM pn, making it more suitable for time-resolved spectroscopy.
  • Method: Folded 830 ks NGC 3783 HETG/MEG spectrum through the Suzaku XIS BI response and then through the XMM response.
hotgas home of the grating archive spectra http hotgas pha jhu edu
HotGAS: Home of the Grating Archive Spectra
  • Origin & location of ionized outflows still uncertain.
  • X-ray columns ~1021-22 cm-2, x ~ 101-3, sometimes in same source.
  • Location, Ne, X-ray cov/fill factor (C) require variability studies. (Chandra monitoring of NGC 3783 gave only upper limit on R, < 6 pc. Origin may still be at accretion disk, but detection may only be possible for matter further out).
  • Can only measure absolute mass outflow rate when C is known. If C is similar in different AGN, we find a tentative connection between mass flow and accretion efficiency. For large C, mass outflow rate comparable to accretion rate (~0.01-0.1 solar M/year).
  • Tentative connection between outflow velocity and accretion efficiency, independent of C. Bimodal V?
  • Some very high V outflows in QSOs may be really be due to z~ 0, local absorption (whigm?). However, the implied column density for whigm is way too high. There are low V interpretations also.
  • Rich & new phenomenology of Fe K emission with Chandra & XMM: Need to disentangle the disk & DM components.